/* ** 2010 February 1 ** ** The author disclaims copyright to this source code. In place of ** a legal notice, here is a blessing: ** ** May you do good and not evil. ** May you find forgiveness for yourself and forgive others. ** May you share freely, never taking more than you give. ** ************************************************************************* ** ** This file contains the implementation of a write-ahead log (WAL) used in ** "journal_mode=WAL" mode. ** ** WRITE-AHEAD LOG (WAL) FILE FORMAT ** ** A WAL file consists of a header followed by zero or more "frames". ** Each frame records the revised content of a single page from the ** database file. All changes to the database are recorded by writing ** frames into the WAL. Transactions commit when a frame is written that ** contains a commit marker. A single WAL can and usually does record ** multiple transactions. Periodically, the content of the WAL is ** transferred back into the database file in an operation called a ** "checkpoint". ** ** A single WAL file can be used multiple times. In other words, the ** WAL can fill up with frames and then be checkpointed and then new ** frames can overwrite the old ones. A WAL always grows from beginning ** toward the end. Checksums and counters attached to each frame are ** used to determine which frames within the WAL are valid and which ** are leftovers from prior checkpoints. ** ** The WAL header is 32 bytes in size and consists of the following eight ** big-endian 32-bit unsigned integer values: ** ** 0: Magic number. 0x377f0682 or 0x377f0683 ** 4: File format version. Currently 3007000 ** 8: Database page size. Example: 1024 ** 12: Checkpoint sequence number ** 16: Salt-1, random integer incremented with each checkpoint ** 20: Salt-2, a different random integer changing with each ckpt ** 24: Checksum-1 (first part of checksum for first 24 bytes of header). ** 28: Checksum-2 (second part of checksum for first 24 bytes of header). ** ** Immediately following the wal-header are zero or more frames. Each ** frame consists of a 24-byte frame-header followed by a bytes ** of page data. The frame-header is six big-endian 32-bit unsigned ** integer values, as follows: ** ** 0: Page number. ** 4: For commit records, the size of the database image in pages ** after the commit. For all other records, zero. ** 8: Salt-1 (copied from the header) ** 12: Salt-2 (copied from the header) ** 16: Checksum-1. ** 20: Checksum-2. ** ** A frame is considered valid if and only if the following conditions are ** true: ** ** (1) The salt-1 and salt-2 values in the frame-header match ** salt values in the wal-header ** ** (2) The checksum values in the final 8 bytes of the frame-header ** exactly match the checksum computed consecutively on the ** WAL header and the first 8 bytes and the content of all frames ** up to and including the current frame. ** ** The checksum is computed using 32-bit big-endian integers if the ** magic number in the first 4 bytes of the WAL is 0x377f0683 and it ** is computed using little-endian if the magic number is 0x377f0682. ** The checksum values are always stored in the frame header in a ** big-endian format regardless of which byte order is used to compute ** the checksum. The checksum is computed by interpreting the input as ** an even number of unsigned 32-bit integers: x[0] through x[N]. The ** algorithm used for the checksum is as follows: ** ** for i from 0 to n-1 step 2: ** s0 += x[i] + s1; ** s1 += x[i+1] + s0; ** endfor ** ** Note that s0 and s1 are both weighted checksums using fibonacci weights ** in reverse order (the largest fibonacci weight occurs on the first element ** of the sequence being summed.) The s1 value spans all 32-bit ** terms of the sequence whereas s0 omits the final term. ** ** On a checkpoint, the WAL is first VFS.xSync-ed, then valid content of the ** WAL is transferred into the database, then the database is VFS.xSync-ed. ** The VFS.xSync operations serve as write barriers - all writes launched ** before the xSync must complete before any write that launches after the ** xSync begins. ** ** After each checkpoint, the salt-1 value is incremented and the salt-2 ** value is randomized. This prevents old and new frames in the WAL from ** being considered valid at the same time and being checkpointing together ** following a crash. ** ** READER ALGORITHM ** ** To read a page from the database (call it page number P), a reader ** first checks the WAL to see if it contains page P. If so, then the ** last valid instance of page P that is a followed by a commit frame ** or is a commit frame itself becomes the value read. If the WAL ** contains no copies of page P that are valid and which are a commit ** frame or are followed by a commit frame, then page P is read from ** the database file. ** ** To start a read transaction, the reader records the index of the last ** valid frame in the WAL. The reader uses this recorded "mxFrame" value ** for all subsequent read operations. New transactions can be appended ** to the WAL, but as long as the reader uses its original mxFrame value ** and ignores the newly appended content, it will see a consistent snapshot ** of the database from a single point in time. This technique allows ** multiple concurrent readers to view different versions of the database ** content simultaneously. ** ** The reader algorithm in the previous paragraphs works correctly, but ** because frames for page P can appear anywhere within the WAL, the ** reader has to scan the entire WAL looking for page P frames. If the ** WAL is large (multiple megabytes is typical) that scan can be slow, ** and read performance suffers. To overcome this problem, a separate ** data structure called the wal-index is maintained to expedite the ** search for frames of a particular page. ** ** WAL-INDEX FORMAT ** ** Conceptually, the wal-index is shared memory, though VFS implementations ** might choose to implement the wal-index using a mmapped file. Because ** the wal-index is shared memory, SQLite does not support journal_mode=WAL ** on a network filesystem. All users of the database must be able to ** share memory. ** ** The wal-index is transient. After a crash, the wal-index can (and should ** be) reconstructed from the original WAL file. In fact, the VFS is required ** to either truncate or zero the header of the wal-index when the last ** connection to it closes. Because the wal-index is transient, it can ** use an architecture-specific format; it does not have to be cross-platform. ** Hence, unlike the database and WAL file formats which store all values ** as big endian, the wal-index can store multi-byte values in the native ** byte order of the host computer. ** ** The purpose of the wal-index is to answer this question quickly: Given ** a page number P and a maximum frame index M, return the index of the ** last frame in the wal before frame M for page P in the WAL, or return ** NULL if there are no frames for page P in the WAL prior to M. ** ** The wal-index consists of a header region, followed by an one or ** more index blocks. ** ** The wal-index header contains the total number of frames within the WAL ** in the mxFrame field. ** ** Each index block except for the first contains information on ** HASHTABLE_NPAGE frames. The first index block contains information on ** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and ** HASHTABLE_NPAGE are selected so that together the wal-index header and ** first index block are the same size as all other index blocks in the ** wal-index. ** ** Each index block contains two sections, a page-mapping that contains the ** database page number associated with each wal frame, and a hash-table ** that allows readers to query an index block for a specific page number. ** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE ** for the first index block) 32-bit page numbers. The first entry in the ** first index-block contains the database page number corresponding to the ** first frame in the WAL file. The first entry in the second index block ** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in ** the log, and so on. ** ** The last index block in a wal-index usually contains less than the full ** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers, ** depending on the contents of the WAL file. This does not change the ** allocated size of the page-mapping array - the page-mapping array merely ** contains unused entries. ** ** Even without using the hash table, the last frame for page P ** can be found by scanning the page-mapping sections of each index block ** starting with the last index block and moving toward the first, and ** within each index block, starting at the end and moving toward the ** beginning. The first entry that equals P corresponds to the frame ** holding the content for that page. ** ** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers. ** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the ** hash table for each page number in the mapping section, so the hash ** table is never more than half full. The expected number of collisions ** prior to finding a match is 1. Each entry of the hash table is an ** 1-based index of an entry in the mapping section of the same ** index block. Let K be the 1-based index of the largest entry in ** the mapping section. (For index blocks other than the last, K will ** always be exactly HASHTABLE_NPAGE (4096) and for the last index block ** K will be (mxFrame%HASHTABLE_NPAGE).) Unused slots of the hash table ** contain a value of 0. ** ** To look for page P in the hash table, first compute a hash iKey on ** P as follows: ** ** iKey = (P * 383) % HASHTABLE_NSLOT ** ** Then start scanning entries of the hash table, starting with iKey ** (wrapping around to the beginning when the end of the hash table is ** reached) until an unused hash slot is found. Let the first unused slot ** be at index iUnused. (iUnused might be less than iKey if there was ** wrap-around.) Because the hash table is never more than half full, ** the search is guaranteed to eventually hit an unused entry. Let ** iMax be the value between iKey and iUnused, closest to iUnused, ** where aHash[iMax]==P. If there is no iMax entry (if there exists ** no hash slot such that aHash[i]==p) then page P is not in the ** current index block. Otherwise the iMax-th mapping entry of the ** current index block corresponds to the last entry that references ** page P. ** ** A hash search begins with the last index block and moves toward the ** first index block, looking for entries corresponding to page P. On ** average, only two or three slots in each index block need to be ** examined in order to either find the last entry for page P, or to ** establish that no such entry exists in the block. Each index block ** holds over 4000 entries. So two or three index blocks are sufficient ** to cover a typical 10 megabyte WAL file, assuming 1K pages. 8 or 10 ** comparisons (on average) suffice to either locate a frame in the ** WAL or to establish that the frame does not exist in the WAL. This ** is much faster than scanning the entire 10MB WAL. ** ** Note that entries are added in order of increasing K. Hence, one ** reader might be using some value K0 and a second reader that started ** at a later time (after additional transactions were added to the WAL ** and to the wal-index) might be using a different value K1, where K1>K0. ** Both readers can use the same hash table and mapping section to get ** the correct result. There may be entries in the hash table with ** K>K0 but to the first reader, those entries will appear to be unused ** slots in the hash table and so the first reader will get an answer as ** if no values greater than K0 had ever been inserted into the hash table ** in the first place - which is what reader one wants. Meanwhile, the ** second reader using K1 will see additional values that were inserted ** later, which is exactly what reader two wants. ** ** When a rollback occurs, the value of K is decreased. Hash table entries ** that correspond to frames greater than the new K value are removed ** from the hash table at this point. */ #ifndef SQLITE_OMIT_WAL #include "wal.h" /* ** Trace output macros */ #if defined(SQLITE_TEST) && defined(SQLITE_DEBUG) int sqlite3WalTrace = 0; # define WALTRACE(X) if(sqlite3WalTrace) sqlite3DebugPrintf X #else # define WALTRACE(X) #endif /* ** The maximum (and only) versions of the wal and wal-index formats ** that may be interpreted by this version of SQLite. ** ** If a client begins recovering a WAL file and finds that (a) the checksum ** values in the wal-header are correct and (b) the version field is not ** WAL_MAX_VERSION, recovery fails and SQLite returns SQLITE_CANTOPEN. ** ** Similarly, if a client successfully reads a wal-index header (i.e. the ** checksum test is successful) and finds that the version field is not ** WALINDEX_MAX_VERSION, then no read-transaction is opened and SQLite ** returns SQLITE_CANTOPEN. */ #define WAL_MAX_VERSION 3007000 #define WALINDEX_MAX_VERSION 3007000 /* ** Indices of various locking bytes. WAL_NREADER is the number ** of available reader locks and should be at least 3. The default ** is SQLITE_SHM_NLOCK==8 and WAL_NREADER==5. */ #define WAL_WRITE_LOCK 0 #define WAL_ALL_BUT_WRITE 1 #define WAL_CKPT_LOCK 1 #define WAL_RECOVER_LOCK 2 #define WAL_READ_LOCK(I) (3+(I)) #define WAL_NREADER (SQLITE_SHM_NLOCK-3) /* Object declarations */ typedef struct WalIndexHdr WalIndexHdr; typedef struct WalIterator WalIterator; typedef struct WalCkptInfo WalCkptInfo; /* ** The following object holds a copy of the wal-index header content. ** ** The actual header in the wal-index consists of two copies of this ** object followed by one instance of the WalCkptInfo object. ** For all versions of SQLite through 3.10.0 and probably beyond, ** the locking bytes (WalCkptInfo.aLock) start at offset 120 and ** the total header size is 136 bytes. ** ** The szPage value can be any power of 2 between 512 and 32768, inclusive. ** Or it can be 1 to represent a 65536-byte page. The latter case was ** added in 3.7.1 when support for 64K pages was added. */ struct WalIndexHdr { u32 iVersion; /* Wal-index version */ u32 unused; /* Unused (padding) field */ u32 iChange; /* Counter incremented each transaction */ u8 isInit; /* 1 when initialized */ u8 bigEndCksum; /* True if checksums in WAL are big-endian */ u16 szPage; /* Database page size in bytes. 1==64K */ u32 mxFrame; /* Index of last valid frame in the WAL */ u32 nPage; /* Size of database in pages */ u32 aFrameCksum[2]; /* Checksum of last frame in log */ u32 aSalt[2]; /* Two salt values copied from WAL header */ u32 aCksum[2]; /* Checksum over all prior fields */ }; /* ** A copy of the following object occurs in the wal-index immediately ** following the second copy of the WalIndexHdr. This object stores ** information used by checkpoint. ** ** nBackfill is the number of frames in the WAL that have been written ** back into the database. (We call the act of moving content from WAL to ** database "backfilling".) The nBackfill number is never greater than ** WalIndexHdr.mxFrame. nBackfill can only be increased by threads ** holding the WAL_CKPT_LOCK lock (which includes a recovery thread). ** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from ** mxFrame back to zero when the WAL is reset. ** ** nBackfillAttempted is the largest value of nBackfill that a checkpoint ** has attempted to achieve. Normally nBackfill==nBackfillAtempted, however ** the nBackfillAttempted is set before any backfilling is done and the ** nBackfill is only set after all backfilling completes. So if a checkpoint ** crashes, nBackfillAttempted might be larger than nBackfill. The ** WalIndexHdr.mxFrame must never be less than nBackfillAttempted. ** ** The aLock[] field is a set of bytes used for locking. These bytes should ** never be read or written. ** ** There is one entry in aReadMark[] for each reader lock. If a reader ** holds read-lock K, then the value in aReadMark[K] is no greater than ** the mxFrame for that reader. The value READMARK_NOT_USED (0xffffffff) ** for any aReadMark[] means that entry is unused. aReadMark[0] is ** a special case; its value is never used and it exists as a place-holder ** to avoid having to offset aReadMark[] indexs by one. Readers holding ** WAL_READ_LOCK(0) always ignore the entire WAL and read all content ** directly from the database. ** ** The value of aReadMark[K] may only be changed by a thread that ** is holding an exclusive lock on WAL_READ_LOCK(K). Thus, the value of ** aReadMark[K] cannot changed while there is a reader is using that mark ** since the reader will be holding a shared lock on WAL_READ_LOCK(K). ** ** The checkpointer may only transfer frames from WAL to database where ** the frame numbers are less than or equal to every aReadMark[] that is ** in use (that is, every aReadMark[j] for which there is a corresponding ** WAL_READ_LOCK(j)). New readers (usually) pick the aReadMark[] with the ** largest value and will increase an unused aReadMark[] to mxFrame if there ** is not already an aReadMark[] equal to mxFrame. The exception to the ** previous sentence is when nBackfill equals mxFrame (meaning that everything ** in the WAL has been backfilled into the database) then new readers ** will choose aReadMark[0] which has value 0 and hence such reader will ** get all their all content directly from the database file and ignore ** the WAL. ** ** Writers normally append new frames to the end of the WAL. However, ** if nBackfill equals mxFrame (meaning that all WAL content has been ** written back into the database) and if no readers are using the WAL ** (in other words, if there are no WAL_READ_LOCK(i) where i>0) then ** the writer will first "reset" the WAL back to the beginning and start ** writing new content beginning at frame 1. ** ** We assume that 32-bit loads are atomic and so no locks are needed in ** order to read from any aReadMark[] entries. */ struct WalCkptInfo { u32 nBackfill; /* Number of WAL frames backfilled into DB */ u32 aReadMark[WAL_NREADER]; /* Reader marks */ u8 aLock[SQLITE_SHM_NLOCK]; /* Reserved space for locks */ u32 nBackfillAttempted; /* WAL frames perhaps written, or maybe not */ u32 notUsed0; /* Available for future enhancements */ }; #define READMARK_NOT_USED 0xffffffff /* A block of WALINDEX_LOCK_RESERVED bytes beginning at ** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems ** only support mandatory file-locks, we do not read or write data ** from the region of the file on which locks are applied. */ #define WALINDEX_LOCK_OFFSET (sizeof(WalIndexHdr)*2+offsetof(WalCkptInfo,aLock)) #define WALINDEX_HDR_SIZE (sizeof(WalIndexHdr)*2+sizeof(WalCkptInfo)) /* Size of header before each frame in wal */ #define WAL_FRAME_HDRSIZE 24 /* Size of write ahead log header, including checksum. */ /* #define WAL_HDRSIZE 24 */ #define WAL_HDRSIZE 32 /* WAL magic value. Either this value, or the same value with the least ** significant bit also set (WAL_MAGIC | 0x00000001) is stored in 32-bit ** big-endian format in the first 4 bytes of a WAL file. ** ** If the LSB is set, then the checksums for each frame within the WAL ** file are calculated by treating all data as an array of 32-bit ** big-endian words. Otherwise, they are calculated by interpreting ** all data as 32-bit little-endian words. */ #define WAL_MAGIC 0x377f0682 /* ** Return the offset of frame iFrame in the write-ahead log file, ** assuming a database page size of szPage bytes. The offset returned ** is to the start of the write-ahead log frame-header. */ #define walFrameOffset(iFrame, szPage) ( \ WAL_HDRSIZE + ((iFrame)-1)*(i64)((szPage)+WAL_FRAME_HDRSIZE) \ ) /* ** An open write-ahead log file is represented by an instance of the ** following object. */ struct Wal { sqlite3_vfs *pVfs; /* The VFS used to create pDbFd */ sqlite3_file *pDbFd; /* File handle for the database file */ sqlite3_file *pWalFd; /* File handle for WAL file */ u32 iCallback; /* Value to pass to log callback (or 0) */ i64 mxWalSize; /* Truncate WAL to this size upon reset */ int nWiData; /* Size of array apWiData */ int szFirstBlock; /* Size of first block written to WAL file */ volatile u32 **apWiData; /* Pointer to wal-index content in memory */ u32 szPage; /* Database page size */ i16 readLock; /* Which read lock is being held. -1 for none */ u8 syncFlags; /* Flags to use to sync header writes */ u8 exclusiveMode; /* Non-zero if connection is in exclusive mode */ u8 writeLock; /* True if in a write transaction */ u8 ckptLock; /* True if holding a checkpoint lock */ u8 readOnly; /* WAL_RDWR, WAL_RDONLY, or WAL_SHM_RDONLY */ u8 truncateOnCommit; /* True to truncate WAL file on commit */ u8 syncHeader; /* Fsync the WAL header if true */ u8 padToSectorBoundary; /* Pad transactions out to the next sector */ WalIndexHdr hdr; /* Wal-index header for current transaction */ u32 minFrame; /* Ignore wal frames before this one */ u32 iReCksum; /* On commit, recalculate checksums from here */ const char *zWalName; /* Name of WAL file */ u32 nCkpt; /* Checkpoint sequence counter in the wal-header */ #ifdef SQLITE_DEBUG u8 lockError; /* True if a locking error has occurred */ #endif #ifdef SQLITE_ENABLE_SNAPSHOT WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */ #endif }; /* ** Candidate values for Wal.exclusiveMode. */ #define WAL_NORMAL_MODE 0 #define WAL_EXCLUSIVE_MODE 1 #define WAL_HEAPMEMORY_MODE 2 /* ** Possible values for WAL.readOnly */ #define WAL_RDWR 0 /* Normal read/write connection */ #define WAL_RDONLY 1 /* The WAL file is readonly */ #define WAL_SHM_RDONLY 2 /* The SHM file is readonly */ /* ** Each page of the wal-index mapping contains a hash-table made up of ** an array of HASHTABLE_NSLOT elements of the following type. */ typedef u16 ht_slot; /* ** This structure is used to implement an iterator that loops through ** all frames in the WAL in database page order. Where two or more frames ** correspond to the same database page, the iterator visits only the ** frame most recently written to the WAL (in other words, the frame with ** the largest index). ** ** The internals of this structure are only accessed by: ** ** walIteratorInit() - Create a new iterator, ** walIteratorNext() - Step an iterator, ** walIteratorFree() - Free an iterator. ** ** This functionality is used by the checkpoint code (see walCheckpoint()). */ struct WalIterator { int iPrior; /* Last result returned from the iterator */ int nSegment; /* Number of entries in aSegment[] */ struct WalSegment { int iNext; /* Next slot in aIndex[] not yet returned */ ht_slot *aIndex; /* i0, i1, i2... such that aPgno[iN] ascend */ u32 *aPgno; /* Array of page numbers. */ int nEntry; /* Nr. of entries in aPgno[] and aIndex[] */ int iZero; /* Frame number associated with aPgno[0] */ } aSegment[1]; /* One for every 32KB page in the wal-index */ }; /* ** Define the parameters of the hash tables in the wal-index file. There ** is a hash-table following every HASHTABLE_NPAGE page numbers in the ** wal-index. ** ** Changing any of these constants will alter the wal-index format and ** create incompatibilities. */ #define HASHTABLE_NPAGE 4096 /* Must be power of 2 */ #define HASHTABLE_HASH_1 383 /* Should be prime */ #define HASHTABLE_NSLOT (HASHTABLE_NPAGE*2) /* Must be a power of 2 */ /* ** The block of page numbers associated with the first hash-table in a ** wal-index is smaller than usual. This is so that there is a complete ** hash-table on each aligned 32KB page of the wal-index. */ #define HASHTABLE_NPAGE_ONE (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32))) /* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */ #define WALINDEX_PGSZ ( \ sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \ ) /* ** Obtain a pointer to the iPage'th page of the wal-index. The wal-index ** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are ** numbered from zero. ** ** If this call is successful, *ppPage is set to point to the wal-index ** page and SQLITE_OK is returned. If an error (an OOM or VFS error) occurs, ** then an SQLite error code is returned and *ppPage is set to 0. */ static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){ int rc = SQLITE_OK; /* Enlarge the pWal->apWiData[] array if required */ if( pWal->nWiData<=iPage ){ int nByte = sizeof(u32*)*(iPage+1); volatile u32 **apNew; apNew = (volatile u32 **)sqlite3_realloc64((void *)pWal->apWiData, nByte); if( !apNew ){ *ppPage = 0; return SQLITE_NOMEM_BKPT; } memset((void*)&apNew[pWal->nWiData], 0, sizeof(u32*)*(iPage+1-pWal->nWiData)); pWal->apWiData = apNew; pWal->nWiData = iPage+1; } /* Request a pointer to the required page from the VFS */ if( pWal->apWiData[iPage]==0 ){ if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){ pWal->apWiData[iPage] = (u32 volatile *)sqlite3MallocZero(WALINDEX_PGSZ); if( !pWal->apWiData[iPage] ) rc = SQLITE_NOMEM_BKPT; }else{ rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, pWal->writeLock, (void volatile **)&pWal->apWiData[iPage] ); if( rc==SQLITE_READONLY ){ pWal->readOnly |= WAL_SHM_RDONLY; rc = SQLITE_OK; } } } *ppPage = pWal->apWiData[iPage]; assert( iPage==0 || *ppPage || rc!=SQLITE_OK ); return rc; } /* ** Return a pointer to the WalCkptInfo structure in the wal-index. */ static volatile WalCkptInfo *walCkptInfo(Wal *pWal){ assert( pWal->nWiData>0 && pWal->apWiData[0] ); return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]); } /* ** Return a pointer to the WalIndexHdr structure in the wal-index. */ static volatile WalIndexHdr *walIndexHdr(Wal *pWal){ assert( pWal->nWiData>0 && pWal->apWiData[0] ); return (volatile WalIndexHdr*)pWal->apWiData[0]; } /* ** The argument to this macro must be of type u32. On a little-endian ** architecture, it returns the u32 value that results from interpreting ** the 4 bytes as a big-endian value. On a big-endian architecture, it ** returns the value that would be produced by interpreting the 4 bytes ** of the input value as a little-endian integer. */ #define BYTESWAP32(x) ( \ (((x)&0x000000FF)<<24) + (((x)&0x0000FF00)<<8) \ + (((x)&0x00FF0000)>>8) + (((x)&0xFF000000)>>24) \ ) /* ** Generate or extend an 8 byte checksum based on the data in ** array aByte[] and the initial values of aIn[0] and aIn[1] (or ** initial values of 0 and 0 if aIn==NULL). ** ** The checksum is written back into aOut[] before returning. ** ** nByte must be a positive multiple of 8. */ static void walChecksumBytes( int nativeCksum, /* True for native byte-order, false for non-native */ u8 *a, /* Content to be checksummed */ int nByte, /* Bytes of content in a[]. Must be a multiple of 8. */ const u32 *aIn, /* Initial checksum value input */ u32 *aOut /* OUT: Final checksum value output */ ){ u32 s1, s2; u32 *aData = (u32 *)a; u32 *aEnd = (u32 *)&a[nByte]; if( aIn ){ s1 = aIn[0]; s2 = aIn[1]; }else{ s1 = s2 = 0; } assert( nByte>=8 ); assert( (nByte&0x00000007)==0 ); if( nativeCksum ){ do { s1 += *aData++ + s2; s2 += *aData++ + s1; }while( aDataexclusiveMode!=WAL_HEAPMEMORY_MODE ){ sqlite3OsShmBarrier(pWal->pDbFd); } } /* ** Write the header information in pWal->hdr into the wal-index. ** ** The checksum on pWal->hdr is updated before it is written. */ static void walIndexWriteHdr(Wal *pWal){ volatile WalIndexHdr *aHdr = walIndexHdr(pWal); const int nCksum = offsetof(WalIndexHdr, aCksum); assert( pWal->writeLock ); pWal->hdr.isInit = 1; pWal->hdr.iVersion = WALINDEX_MAX_VERSION; walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum); memcpy((void*)&aHdr[1], (const void*)&pWal->hdr, sizeof(WalIndexHdr)); walShmBarrier(pWal); memcpy((void*)&aHdr[0], (const void*)&pWal->hdr, sizeof(WalIndexHdr)); } /* ** This function encodes a single frame header and writes it to a buffer ** supplied by the caller. A frame-header is made up of a series of ** 4-byte big-endian integers, as follows: ** ** 0: Page number. ** 4: For commit records, the size of the database image in pages ** after the commit. For all other records, zero. ** 8: Salt-1 (copied from the wal-header) ** 12: Salt-2 (copied from the wal-header) ** 16: Checksum-1. ** 20: Checksum-2. */ static void walEncodeFrame( Wal *pWal, /* The write-ahead log */ u32 iPage, /* Database page number for frame */ u32 nTruncate, /* New db size (or 0 for non-commit frames) */ u8 *aData, /* Pointer to page data */ u8 *aFrame /* OUT: Write encoded frame here */ ){ int nativeCksum; /* True for native byte-order checksums */ u32 *aCksum = pWal->hdr.aFrameCksum; assert( WAL_FRAME_HDRSIZE==24 ); sqlite3Put4byte(&aFrame[0], iPage); sqlite3Put4byte(&aFrame[4], nTruncate); if( pWal->iReCksum==0 ){ memcpy(&aFrame[8], pWal->hdr.aSalt, 8); nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN); walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum); walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum); sqlite3Put4byte(&aFrame[16], aCksum[0]); sqlite3Put4byte(&aFrame[20], aCksum[1]); }else{ memset(&aFrame[8], 0, 16); } } /* ** Check to see if the frame with header in aFrame[] and content ** in aData[] is valid. If it is a valid frame, fill *piPage and ** *pnTruncate and return true. Return if the frame is not valid. */ static int walDecodeFrame( Wal *pWal, /* The write-ahead log */ u32 *piPage, /* OUT: Database page number for frame */ u32 *pnTruncate, /* OUT: New db size (or 0 if not commit) */ u8 *aData, /* Pointer to page data (for checksum) */ u8 *aFrame /* Frame data */ ){ int nativeCksum; /* True for native byte-order checksums */ u32 *aCksum = pWal->hdr.aFrameCksum; u32 pgno; /* Page number of the frame */ assert( WAL_FRAME_HDRSIZE==24 ); /* A frame is only valid if the salt values in the frame-header ** match the salt values in the wal-header. */ if( memcmp(&pWal->hdr.aSalt, &aFrame[8], 8)!=0 ){ return 0; } /* A frame is only valid if the page number is creater than zero. */ pgno = sqlite3Get4byte(&aFrame[0]); if( pgno==0 ){ return 0; } /* A frame is only valid if a checksum of the WAL header, ** all prior frams, the first 16 bytes of this frame-header, ** and the frame-data matches the checksum in the last 8 ** bytes of this frame-header. */ nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN); walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum); walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum); if( aCksum[0]!=sqlite3Get4byte(&aFrame[16]) || aCksum[1]!=sqlite3Get4byte(&aFrame[20]) ){ /* Checksum failed. */ return 0; } /* If we reach this point, the frame is valid. Return the page number ** and the new database size. */ *piPage = pgno; *pnTruncate = sqlite3Get4byte(&aFrame[4]); return 1; } #if defined(SQLITE_TEST) && defined(SQLITE_DEBUG) /* ** Names of locks. This routine is used to provide debugging output and is not ** a part of an ordinary build. */ static const char *walLockName(int lockIdx){ if( lockIdx==WAL_WRITE_LOCK ){ return "WRITE-LOCK"; }else if( lockIdx==WAL_CKPT_LOCK ){ return "CKPT-LOCK"; }else if( lockIdx==WAL_RECOVER_LOCK ){ return "RECOVER-LOCK"; }else{ static char zName[15]; sqlite3_snprintf(sizeof(zName), zName, "READ-LOCK[%d]", lockIdx-WAL_READ_LOCK(0)); return zName; } } #endif /*defined(SQLITE_TEST) || defined(SQLITE_DEBUG) */ /* ** Set or release locks on the WAL. Locks are either shared or exclusive. ** A lock cannot be moved directly between shared and exclusive - it must go ** through the unlocked state first. ** ** In locking_mode=EXCLUSIVE, all of these routines become no-ops. */ static int walLockShared(Wal *pWal, int lockIdx){ int rc; if( pWal->exclusiveMode ) return SQLITE_OK; rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1, SQLITE_SHM_LOCK | SQLITE_SHM_SHARED); WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal, walLockName(lockIdx), rc ? "failed" : "ok")); VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && rc!=SQLITE_BUSY); ) return rc; } static void walUnlockShared(Wal *pWal, int lockIdx){ if( pWal->exclusiveMode ) return; (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1, SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED); WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx))); } static int walLockExclusive(Wal *pWal, int lockIdx, int n){ int rc; if( pWal->exclusiveMode ) return SQLITE_OK; rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, n, SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE); WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal, walLockName(lockIdx), n, rc ? "failed" : "ok")); VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && rc!=SQLITE_BUSY); ) return rc; } static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){ if( pWal->exclusiveMode ) return; (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n, SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE); WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal, walLockName(lockIdx), n)); } /* ** Compute a hash on a page number. The resulting hash value must land ** between 0 and (HASHTABLE_NSLOT-1). The walHashNext() function advances ** the hash to the next value in the event of a collision. */ static int walHash(u32 iPage){ assert( iPage>0 ); assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 ); return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1); } static int walNextHash(int iPriorHash){ return (iPriorHash+1)&(HASHTABLE_NSLOT-1); } /* ** Return pointers to the hash table and page number array stored on ** page iHash of the wal-index. The wal-index is broken into 32KB pages ** numbered starting from 0. ** ** Set output variable *paHash to point to the start of the hash table ** in the wal-index file. Set *piZero to one less than the frame ** number of the first frame indexed by this hash table. If a ** slot in the hash table is set to N, it refers to frame number ** (*piZero+N) in the log. ** ** Finally, set *paPgno so that *paPgno[1] is the page number of the ** first frame indexed by the hash table, frame (*piZero+1). */ static int walHashGet( Wal *pWal, /* WAL handle */ int iHash, /* Find the iHash'th table */ volatile ht_slot **paHash, /* OUT: Pointer to hash index */ volatile u32 **paPgno, /* OUT: Pointer to page number array */ u32 *piZero /* OUT: Frame associated with *paPgno[0] */ ){ int rc; /* Return code */ volatile u32 *aPgno; rc = walIndexPage(pWal, iHash, &aPgno); assert( rc==SQLITE_OK || iHash>0 ); if( rc==SQLITE_OK ){ u32 iZero; volatile ht_slot *aHash; aHash = (volatile ht_slot *)&aPgno[HASHTABLE_NPAGE]; if( iHash==0 ){ aPgno = &aPgno[WALINDEX_HDR_SIZE/sizeof(u32)]; iZero = 0; }else{ iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE; } *paPgno = &aPgno[-1]; *paHash = aHash; *piZero = iZero; } return rc; } /* ** Return the number of the wal-index page that contains the hash-table ** and page-number array that contain entries corresponding to WAL frame ** iFrame. The wal-index is broken up into 32KB pages. Wal-index pages ** are numbered starting from 0. */ static int walFramePage(u32 iFrame){ int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE; assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE) && (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE) && (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)) && (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE) && (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE)) ); return iHash; } /* ** Return the page number associated with frame iFrame in this WAL. */ static u32 walFramePgno(Wal *pWal, u32 iFrame){ int iHash = walFramePage(iFrame); if( iHash==0 ){ return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1]; } return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE]; } /* ** Remove entries from the hash table that point to WAL slots greater ** than pWal->hdr.mxFrame. ** ** This function is called whenever pWal->hdr.mxFrame is decreased due ** to a rollback or savepoint. ** ** At most only the hash table containing pWal->hdr.mxFrame needs to be ** updated. Any later hash tables will be automatically cleared when ** pWal->hdr.mxFrame advances to the point where those hash tables are ** actually needed. */ static void walCleanupHash(Wal *pWal){ volatile ht_slot *aHash = 0; /* Pointer to hash table to clear */ volatile u32 *aPgno = 0; /* Page number array for hash table */ u32 iZero = 0; /* frame == (aHash[x]+iZero) */ int iLimit = 0; /* Zero values greater than this */ int nByte; /* Number of bytes to zero in aPgno[] */ int i; /* Used to iterate through aHash[] */ assert( pWal->writeLock ); testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE-1 ); testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE ); testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE+1 ); if( pWal->hdr.mxFrame==0 ) return; /* Obtain pointers to the hash-table and page-number array containing ** the entry that corresponds to frame pWal->hdr.mxFrame. It is guaranteed ** that the page said hash-table and array reside on is already mapped. */ assert( pWal->nWiData>walFramePage(pWal->hdr.mxFrame) ); assert( pWal->apWiData[walFramePage(pWal->hdr.mxFrame)] ); walHashGet(pWal, walFramePage(pWal->hdr.mxFrame), &aHash, &aPgno, &iZero); /* Zero all hash-table entries that correspond to frame numbers greater ** than pWal->hdr.mxFrame. */ iLimit = pWal->hdr.mxFrame - iZero; assert( iLimit>0 ); for(i=0; iiLimit ){ aHash[i] = 0; } } /* Zero the entries in the aPgno array that correspond to frames with ** frame numbers greater than pWal->hdr.mxFrame. */ nByte = (int)((char *)aHash - (char *)&aPgno[iLimit+1]); memset((void *)&aPgno[iLimit+1], 0, nByte); #ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT /* Verify that the every entry in the mapping region is still reachable ** via the hash table even after the cleanup. */ if( iLimit ){ int j; /* Loop counter */ int iKey; /* Hash key */ for(j=1; j<=iLimit; j++){ for(iKey=walHash(aPgno[j]); aHash[iKey]; iKey=walNextHash(iKey)){ if( aHash[iKey]==j ) break; } assert( aHash[iKey]==j ); } } #endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */ } /* ** Set an entry in the wal-index that will map database page number ** pPage into WAL frame iFrame. */ static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){ int rc; /* Return code */ u32 iZero = 0; /* One less than frame number of aPgno[1] */ volatile u32 *aPgno = 0; /* Page number array */ volatile ht_slot *aHash = 0; /* Hash table */ rc = walHashGet(pWal, walFramePage(iFrame), &aHash, &aPgno, &iZero); /* Assuming the wal-index file was successfully mapped, populate the ** page number array and hash table entry. */ if( rc==SQLITE_OK ){ int iKey; /* Hash table key */ int idx; /* Value to write to hash-table slot */ int nCollide; /* Number of hash collisions */ idx = iFrame - iZero; assert( idx <= HASHTABLE_NSLOT/2 + 1 ); /* If this is the first entry to be added to this hash-table, zero the ** entire hash table and aPgno[] array before proceeding. */ if( idx==1 ){ int nByte = (int)((u8 *)&aHash[HASHTABLE_NSLOT] - (u8 *)&aPgno[1]); memset((void*)&aPgno[1], 0, nByte); } /* If the entry in aPgno[] is already set, then the previous writer ** must have exited unexpectedly in the middle of a transaction (after ** writing one or more dirty pages to the WAL to free up memory). ** Remove the remnants of that writers uncommitted transaction from ** the hash-table before writing any new entries. */ if( aPgno[idx] ){ walCleanupHash(pWal); assert( !aPgno[idx] ); } /* Write the aPgno[] array entry and the hash-table slot. */ nCollide = idx; for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){ if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT; } aPgno[idx] = iPage; aHash[iKey] = (ht_slot)idx; #ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT /* Verify that the number of entries in the hash table exactly equals ** the number of entries in the mapping region. */ { int i; /* Loop counter */ int nEntry = 0; /* Number of entries in the hash table */ for(i=0; ickptLock==1 || pWal->ckptLock==0 ); assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 ); assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE ); assert( pWal->writeLock ); iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock; nLock = SQLITE_SHM_NLOCK - iLock; rc = walLockExclusive(pWal, iLock, nLock); if( rc ){ return rc; } WALTRACE(("WAL%p: recovery begin...\n", pWal)); memset(&pWal->hdr, 0, sizeof(WalIndexHdr)); rc = sqlite3OsFileSize(pWal->pWalFd, &nSize); if( rc!=SQLITE_OK ){ goto recovery_error; } if( nSize>WAL_HDRSIZE ){ u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */ u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */ int szFrame; /* Number of bytes in buffer aFrame[] */ u8 *aData; /* Pointer to data part of aFrame buffer */ int iFrame; /* Index of last frame read */ i64 iOffset; /* Next offset to read from log file */ int szPage; /* Page size according to the log */ u32 magic; /* Magic value read from WAL header */ u32 version; /* Magic value read from WAL header */ int isValid; /* True if this frame is valid */ /* Read in the WAL header. */ rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0); if( rc!=SQLITE_OK ){ goto recovery_error; } /* If the database page size is not a power of two, or is greater than ** SQLITE_MAX_PAGE_SIZE, conclude that the WAL file contains no valid ** data. Similarly, if the 'magic' value is invalid, ignore the whole ** WAL file. */ magic = sqlite3Get4byte(&aBuf[0]); szPage = sqlite3Get4byte(&aBuf[8]); if( (magic&0xFFFFFFFE)!=WAL_MAGIC || szPage&(szPage-1) || szPage>SQLITE_MAX_PAGE_SIZE || szPage<512 ){ goto finished; } pWal->hdr.bigEndCksum = (u8)(magic&0x00000001); pWal->szPage = szPage; pWal->nCkpt = sqlite3Get4byte(&aBuf[12]); memcpy(&pWal->hdr.aSalt, &aBuf[16], 8); /* Verify that the WAL header checksum is correct */ walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN, aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum ); if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24]) || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28]) ){ goto finished; } /* Verify that the version number on the WAL format is one that ** are able to understand */ version = sqlite3Get4byte(&aBuf[4]); if( version!=WAL_MAX_VERSION ){ rc = SQLITE_CANTOPEN_BKPT; goto finished; } /* Malloc a buffer to read frames into. */ szFrame = szPage + WAL_FRAME_HDRSIZE; aFrame = (u8 *)sqlite3_malloc64(szFrame); if( !aFrame ){ rc = SQLITE_NOMEM_BKPT; goto recovery_error; } aData = &aFrame[WAL_FRAME_HDRSIZE]; /* Read all frames from the log file. */ iFrame = 0; for(iOffset=WAL_HDRSIZE; (iOffset+szFrame)<=nSize; iOffset+=szFrame){ u32 pgno; /* Database page number for frame */ u32 nTruncate; /* dbsize field from frame header */ /* Read and decode the next log frame. */ iFrame++; rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset); if( rc!=SQLITE_OK ) break; isValid = walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame); if( !isValid ) break; rc = walIndexAppend(pWal, iFrame, pgno); if( rc!=SQLITE_OK ) break; /* If nTruncate is non-zero, this is a commit record. */ if( nTruncate ){ pWal->hdr.mxFrame = iFrame; pWal->hdr.nPage = nTruncate; pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16)); testcase( szPage<=32768 ); testcase( szPage>=65536 ); aFrameCksum[0] = pWal->hdr.aFrameCksum[0]; aFrameCksum[1] = pWal->hdr.aFrameCksum[1]; } } sqlite3_free(aFrame); } finished: if( rc==SQLITE_OK ){ volatile WalCkptInfo *pInfo; int i; pWal->hdr.aFrameCksum[0] = aFrameCksum[0]; pWal->hdr.aFrameCksum[1] = aFrameCksum[1]; walIndexWriteHdr(pWal); /* Reset the checkpoint-header. This is safe because this thread is ** currently holding locks that exclude all other readers, writers and ** checkpointers. */ pInfo = walCkptInfo(pWal); pInfo->nBackfill = 0; pInfo->nBackfillAttempted = pWal->hdr.mxFrame; pInfo->aReadMark[0] = 0; for(i=1; iaReadMark[i] = READMARK_NOT_USED; if( pWal->hdr.mxFrame ) pInfo->aReadMark[1] = pWal->hdr.mxFrame; /* If more than one frame was recovered from the log file, report an ** event via sqlite3_log(). This is to help with identifying performance ** problems caused by applications routinely shutting down without ** checkpointing the log file. */ if( pWal->hdr.nPage ){ sqlite3_log(SQLITE_NOTICE_RECOVER_WAL, "recovered %d frames from WAL file %s", pWal->hdr.mxFrame, pWal->zWalName ); } } recovery_error: WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok")); walUnlockExclusive(pWal, iLock, nLock); return rc; } /* ** Close an open wal-index. */ static void walIndexClose(Wal *pWal, int isDelete){ if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){ int i; for(i=0; inWiData; i++){ sqlite3_free((void *)pWal->apWiData[i]); pWal->apWiData[i] = 0; } }else{ sqlite3OsShmUnmap(pWal->pDbFd, isDelete); } } /* ** Open a connection to the WAL file zWalName. The database file must ** already be opened on connection pDbFd. The buffer that zWalName points ** to must remain valid for the lifetime of the returned Wal* handle. ** ** A SHARED lock should be held on the database file when this function ** is called. The purpose of this SHARED lock is to prevent any other ** client from unlinking the WAL or wal-index file. If another process ** were to do this just after this client opened one of these files, the ** system would be badly broken. ** ** If the log file is successfully opened, SQLITE_OK is returned and ** *ppWal is set to point to a new WAL handle. If an error occurs, ** an SQLite error code is returned and *ppWal is left unmodified. */ int sqlite3WalOpen( sqlite3_vfs *pVfs, /* vfs module to open wal and wal-index */ sqlite3_file *pDbFd, /* The open database file */ const char *zWalName, /* Name of the WAL file */ int bNoShm, /* True to run in heap-memory mode */ i64 mxWalSize, /* Truncate WAL to this size on reset */ Wal **ppWal /* OUT: Allocated Wal handle */ ){ int rc; /* Return Code */ Wal *pRet; /* Object to allocate and return */ int flags; /* Flags passed to OsOpen() */ assert( zWalName && zWalName[0] ); assert( pDbFd ); /* In the amalgamation, the os_unix.c and os_win.c source files come before ** this source file. Verify that the #defines of the locking byte offsets ** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value. ** For that matter, if the lock offset ever changes from its initial design ** value of 120, we need to know that so there is an assert() to check it. */ assert( 120==WALINDEX_LOCK_OFFSET ); assert( 136==WALINDEX_HDR_SIZE ); #ifdef WIN_SHM_BASE assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET ); #endif #ifdef UNIX_SHM_BASE assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET ); #endif /* Allocate an instance of struct Wal to return. */ *ppWal = 0; pRet = (Wal*)sqlite3MallocZero(sizeof(Wal) + pVfs->szOsFile); if( !pRet ){ return SQLITE_NOMEM_BKPT; } pRet->pVfs = pVfs; pRet->pWalFd = (sqlite3_file *)&pRet[1]; pRet->pDbFd = pDbFd; pRet->readLock = -1; pRet->mxWalSize = mxWalSize; pRet->zWalName = zWalName; pRet->syncHeader = 1; pRet->padToSectorBoundary = 1; pRet->exclusiveMode = (bNoShm ? WAL_HEAPMEMORY_MODE: WAL_NORMAL_MODE); /* Open file handle on the write-ahead log file. */ flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL); rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags); if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){ pRet->readOnly = WAL_RDONLY; } if( rc!=SQLITE_OK ){ walIndexClose(pRet, 0); sqlite3OsClose(pRet->pWalFd); sqlite3_free(pRet); }else{ int iDC = sqlite3OsDeviceCharacteristics(pDbFd); if( iDC & SQLITE_IOCAP_SEQUENTIAL ){ pRet->syncHeader = 0; } if( iDC & SQLITE_IOCAP_POWERSAFE_OVERWRITE ){ pRet->padToSectorBoundary = 0; } *ppWal = pRet; WALTRACE(("WAL%d: opened\n", pRet)); } return rc; } /* ** Change the size to which the WAL file is trucated on each reset. */ void sqlite3WalLimit(Wal *pWal, i64 iLimit){ if( pWal ) pWal->mxWalSize = iLimit; } /* ** Find the smallest page number out of all pages held in the WAL that ** has not been returned by any prior invocation of this method on the ** same WalIterator object. Write into *piFrame the frame index where ** that page was last written into the WAL. Write into *piPage the page ** number. ** ** Return 0 on success. If there are no pages in the WAL with a page ** number larger than *piPage, then return 1. */ static int walIteratorNext( WalIterator *p, /* Iterator */ u32 *piPage, /* OUT: The page number of the next page */ u32 *piFrame /* OUT: Wal frame index of next page */ ){ u32 iMin; /* Result pgno must be greater than iMin */ u32 iRet = 0xFFFFFFFF; /* 0xffffffff is never a valid page number */ int i; /* For looping through segments */ iMin = p->iPrior; assert( iMin<0xffffffff ); for(i=p->nSegment-1; i>=0; i--){ struct WalSegment *pSegment = &p->aSegment[i]; while( pSegment->iNextnEntry ){ u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]]; if( iPg>iMin ){ if( iPgiZero + pSegment->aIndex[pSegment->iNext]; } break; } pSegment->iNext++; } } *piPage = p->iPrior = iRet; return (iRet==0xFFFFFFFF); } /* ** This function merges two sorted lists into a single sorted list. ** ** aLeft[] and aRight[] are arrays of indices. The sort key is ** aContent[aLeft[]] and aContent[aRight[]]. Upon entry, the following ** is guaranteed for all J0 && nRight>0 ); while( iRight=nRight || aContent[aLeft[iLeft]]=nLeft || aContent[aLeft[iLeft]]>dbpage ); assert( iRight>=nRight || aContent[aRight[iRight]]>dbpage ); } *paRight = aLeft; *pnRight = iOut; memcpy(aLeft, aTmp, sizeof(aTmp[0])*iOut); } /* ** Sort the elements in list aList using aContent[] as the sort key. ** Remove elements with duplicate keys, preferring to keep the ** larger aList[] values. ** ** The aList[] entries are indices into aContent[]. The values in ** aList[] are to be sorted so that for all J0 ); assert( HASHTABLE_NPAGE==(1<<(ArraySize(aSub)-1)) ); for(iList=0; iListaList && p->nList<=(1<aList==&aList[iList&~((2<aList, p->nList, &aMerge, &nMerge, aBuffer); } aSub[iSub].aList = aMerge; aSub[iSub].nList = nMerge; } for(iSub++; iSubnList<=(1<aList==&aList[nList&~((2<aList, p->nList, &aMerge, &nMerge, aBuffer); } } assert( aMerge==aList ); *pnList = nMerge; #ifdef SQLITE_DEBUG { int i; for(i=1; i<*pnList; i++){ assert( aContent[aList[i]] > aContent[aList[i-1]] ); } } #endif } /* ** Free an iterator allocated by walIteratorInit(). */ static void walIteratorFree(WalIterator *p){ sqlite3_free(p); } /* ** Construct a WalInterator object that can be used to loop over all ** pages in the WAL in ascending order. The caller must hold the checkpoint ** lock. ** ** On success, make *pp point to the newly allocated WalInterator object ** return SQLITE_OK. Otherwise, return an error code. If this routine ** returns an error, the value of *pp is undefined. ** ** The calling routine should invoke walIteratorFree() to destroy the ** WalIterator object when it has finished with it. */ static int walIteratorInit(Wal *pWal, WalIterator **pp){ WalIterator *p; /* Return value */ int nSegment; /* Number of segments to merge */ u32 iLast; /* Last frame in log */ int nByte; /* Number of bytes to allocate */ int i; /* Iterator variable */ ht_slot *aTmp; /* Temp space used by merge-sort */ int rc = SQLITE_OK; /* Return Code */ /* This routine only runs while holding the checkpoint lock. And ** it only runs if there is actually content in the log (mxFrame>0). */ assert( pWal->ckptLock && pWal->hdr.mxFrame>0 ); iLast = pWal->hdr.mxFrame; /* Allocate space for the WalIterator object. */ nSegment = walFramePage(iLast) + 1; nByte = sizeof(WalIterator) + (nSegment-1)*sizeof(struct WalSegment) + iLast*sizeof(ht_slot); p = (WalIterator *)sqlite3_malloc64(nByte); if( !p ){ return SQLITE_NOMEM_BKPT; } memset(p, 0, nByte); p->nSegment = nSegment; /* Allocate temporary space used by the merge-sort routine. This block ** of memory will be freed before this function returns. */ aTmp = (ht_slot *)sqlite3_malloc64( sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast) ); if( !aTmp ){ rc = SQLITE_NOMEM_BKPT; } for(i=0; rc==SQLITE_OK && iaSegment[p->nSegment])[iZero]; iZero++; for(j=0; jaSegment[i].iZero = iZero; p->aSegment[i].nEntry = nEntry; p->aSegment[i].aIndex = aIndex; p->aSegment[i].aPgno = (u32 *)aPgno; } } sqlite3_free(aTmp); if( rc!=SQLITE_OK ){ walIteratorFree(p); } *pp = p; return rc; } /* ** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and ** n. If the attempt fails and parameter xBusy is not NULL, then it is a ** busy-handler function. Invoke it and retry the lock until either the ** lock is successfully obtained or the busy-handler returns 0. */ static int walBusyLock( Wal *pWal, /* WAL connection */ int (*xBusy)(void*), /* Function to call when busy */ void *pBusyArg, /* Context argument for xBusyHandler */ int lockIdx, /* Offset of first byte to lock */ int n /* Number of bytes to lock */ ){ int rc; do { rc = walLockExclusive(pWal, lockIdx, n); }while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) ); return rc; } /* ** The cache of the wal-index header must be valid to call this function. ** Return the page-size in bytes used by the database. */ static int walPagesize(Wal *pWal){ return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16); } /* ** The following is guaranteed when this function is called: ** ** a) the WRITER lock is held, ** b) the entire log file has been checkpointed, and ** c) any existing readers are reading exclusively from the database ** file - there are no readers that may attempt to read a frame from ** the log file. ** ** This function updates the shared-memory structures so that the next ** client to write to the database (which may be this one) does so by ** writing frames into the start of the log file. ** ** The value of parameter salt1 is used as the aSalt[1] value in the ** new wal-index header. It should be passed a pseudo-random value (i.e. ** one obtained from sqlite3_randomness()). */ static void walRestartHdr(Wal *pWal, u32 salt1){ volatile WalCkptInfo *pInfo = walCkptInfo(pWal); int i; /* Loop counter */ u32 *aSalt = pWal->hdr.aSalt; /* Big-endian salt values */ pWal->nCkpt++; pWal->hdr.mxFrame = 0; sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0])); memcpy(&pWal->hdr.aSalt[1], &salt1, 4); walIndexWriteHdr(pWal); pInfo->nBackfill = 0; pInfo->nBackfillAttempted = 0; pInfo->aReadMark[1] = 0; for(i=2; iaReadMark[i] = READMARK_NOT_USED; assert( pInfo->aReadMark[0]==0 ); } /* ** Copy as much content as we can from the WAL back into the database file ** in response to an sqlite3_wal_checkpoint() request or the equivalent. ** ** The amount of information copies from WAL to database might be limited ** by active readers. This routine will never overwrite a database page ** that a concurrent reader might be using. ** ** All I/O barrier operations (a.k.a fsyncs) occur in this routine when ** SQLite is in WAL-mode in synchronous=NORMAL. That means that if ** checkpoints are always run by a background thread or background ** process, foreground threads will never block on a lengthy fsync call. ** ** Fsync is called on the WAL before writing content out of the WAL and ** into the database. This ensures that if the new content is persistent ** in the WAL and can be recovered following a power-loss or hard reset. ** ** Fsync is also called on the database file if (and only if) the entire ** WAL content is copied into the database file. This second fsync makes ** it safe to delete the WAL since the new content will persist in the ** database file. ** ** This routine uses and updates the nBackfill field of the wal-index header. ** This is the only routine that will increase the value of nBackfill. ** (A WAL reset or recovery will revert nBackfill to zero, but not increase ** its value.) ** ** The caller must be holding sufficient locks to ensure that no other ** checkpoint is running (in any other thread or process) at the same ** time. */ static int walCheckpoint( Wal *pWal, /* Wal connection */ int eMode, /* One of PASSIVE, FULL or RESTART */ int (*xBusy)(void*), /* Function to call when busy */ void *pBusyArg, /* Context argument for xBusyHandler */ int sync_flags, /* Flags for OsSync() (or 0) */ u8 *zBuf /* Temporary buffer to use */ ){ int rc = SQLITE_OK; /* Return code */ int szPage; /* Database page-size */ WalIterator *pIter = 0; /* Wal iterator context */ u32 iDbpage = 0; /* Next database page to write */ u32 iFrame = 0; /* Wal frame containing data for iDbpage */ u32 mxSafeFrame; /* Max frame that can be backfilled */ u32 mxPage; /* Max database page to write */ int i; /* Loop counter */ volatile WalCkptInfo *pInfo; /* The checkpoint status information */ szPage = walPagesize(pWal); testcase( szPage<=32768 ); testcase( szPage>=65536 ); pInfo = walCkptInfo(pWal); if( pInfo->nBackfillhdr.mxFrame ){ /* Allocate the iterator */ rc = walIteratorInit(pWal, &pIter); if( rc!=SQLITE_OK ){ return rc; } assert( pIter ); /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked ** in the SQLITE_CHECKPOINT_PASSIVE mode. */ assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 ); /* Compute in mxSafeFrame the index of the last frame of the WAL that is ** safe to write into the database. Frames beyond mxSafeFrame might ** overwrite database pages that are in use by active readers and thus ** cannot be backfilled from the WAL. */ mxSafeFrame = pWal->hdr.mxFrame; mxPage = pWal->hdr.nPage; for(i=1; iaReadMark[i]; if( mxSafeFrame>y ){ assert( y<=pWal->hdr.mxFrame ); rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1); if( rc==SQLITE_OK ){ pInfo->aReadMark[i] = (i==1 ? mxSafeFrame : READMARK_NOT_USED); walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); }else if( rc==SQLITE_BUSY ){ mxSafeFrame = y; xBusy = 0; }else{ goto walcheckpoint_out; } } } if( pInfo->nBackfillnBackfill; pInfo->nBackfillAttempted = mxSafeFrame; /* Sync the WAL to disk */ if( sync_flags ){ rc = sqlite3OsSync(pWal->pWalFd, sync_flags); } /* If the database may grow as a result of this checkpoint, hint ** about the eventual size of the db file to the VFS layer. */ if( rc==SQLITE_OK ){ i64 nReq = ((i64)mxPage * szPage); rc = sqlite3OsFileSize(pWal->pDbFd, &nSize); if( rc==SQLITE_OK && nSizepDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq); } } /* Iterate through the contents of the WAL, copying data to the db file */ while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){ i64 iOffset; assert( walFramePgno(pWal, iFrame)==iDbpage ); if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ){ continue; } iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE; /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */ rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset); if( rc!=SQLITE_OK ) break; iOffset = (iDbpage-1)*(i64)szPage; testcase( IS_BIG_INT(iOffset) ); rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset); if( rc!=SQLITE_OK ) break; } /* If work was actually accomplished... */ if( rc==SQLITE_OK ){ if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){ i64 szDb = pWal->hdr.nPage*(i64)szPage; testcase( IS_BIG_INT(szDb) ); rc = sqlite3OsTruncate(pWal->pDbFd, szDb); if( rc==SQLITE_OK && sync_flags ){ rc = sqlite3OsSync(pWal->pDbFd, sync_flags); } } if( rc==SQLITE_OK ){ pInfo->nBackfill = mxSafeFrame; } } /* Release the reader lock held while backfilling */ walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1); } if( rc==SQLITE_BUSY ){ /* Reset the return code so as not to report a checkpoint failure ** just because there are active readers. */ rc = SQLITE_OK; } } /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the ** entire wal file has been copied into the database file, then block ** until all readers have finished using the wal file. This ensures that ** the next process to write to the database restarts the wal file. */ if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){ assert( pWal->writeLock ); if( pInfo->nBackfillhdr.mxFrame ){ rc = SQLITE_BUSY; }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){ u32 salt1; sqlite3_randomness(4, &salt1); assert( pInfo->nBackfill==pWal->hdr.mxFrame ); rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1); if( rc==SQLITE_OK ){ if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){ /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as ** SQLITE_CHECKPOINT_RESTART with the addition that it also ** truncates the log file to zero bytes just prior to a ** successful return. ** ** In theory, it might be safe to do this without updating the ** wal-index header in shared memory, as all subsequent reader or ** writer clients should see that the entire log file has been ** checkpointed and behave accordingly. This seems unsafe though, ** as it would leave the system in a state where the contents of ** the wal-index header do not match the contents of the ** file-system. To avoid this, update the wal-index header to ** indicate that the log file contains zero valid frames. */ walRestartHdr(pWal, salt1); rc = sqlite3OsTruncate(pWal->pWalFd, 0); } walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); } } } walcheckpoint_out: walIteratorFree(pIter); return rc; } /* ** If the WAL file is currently larger than nMax bytes in size, truncate ** it to exactly nMax bytes. If an error occurs while doing so, ignore it. */ static void walLimitSize(Wal *pWal, i64 nMax){ i64 sz; int rx; sqlite3BeginBenignMalloc(); rx = sqlite3OsFileSize(pWal->pWalFd, &sz); if( rx==SQLITE_OK && (sz > nMax ) ){ rx = sqlite3OsTruncate(pWal->pWalFd, nMax); } sqlite3EndBenignMalloc(); if( rx ){ sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName); } } /* ** Close a connection to a log file. */ int sqlite3WalClose( Wal *pWal, /* Wal to close */ int sync_flags, /* Flags to pass to OsSync() (or 0) */ int nBuf, u8 *zBuf /* Buffer of at least nBuf bytes */ ){ int rc = SQLITE_OK; if( pWal ){ int isDelete = 0; /* True to unlink wal and wal-index files */ /* If an EXCLUSIVE lock can be obtained on the database file (using the ** ordinary, rollback-mode locking methods, this guarantees that the ** connection associated with this log file is the only connection to ** the database. In this case checkpoint the database and unlink both ** the wal and wal-index files. ** ** The EXCLUSIVE lock is not released before returning. */ rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE); if( rc==SQLITE_OK ){ if( pWal->exclusiveMode==WAL_NORMAL_MODE ){ pWal->exclusiveMode = WAL_EXCLUSIVE_MODE; } rc = sqlite3WalCheckpoint( pWal, SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0 ); if( rc==SQLITE_OK ){ int bPersist = -1; sqlite3OsFileControlHint( pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist ); if( bPersist!=1 ){ /* Try to delete the WAL file if the checkpoint completed and ** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal ** mode (!bPersist) */ isDelete = 1; }else if( pWal->mxWalSize>=0 ){ /* Try to truncate the WAL file to zero bytes if the checkpoint ** completed and fsynced (rc==SQLITE_OK) and we are in persistent ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a ** non-negative value (pWal->mxWalSize>=0). Note that we truncate ** to zero bytes as truncating to the journal_size_limit might ** leave a corrupt WAL file on disk. */ walLimitSize(pWal, 0); } } } walIndexClose(pWal, isDelete); sqlite3OsClose(pWal->pWalFd); if( isDelete ){ sqlite3BeginBenignMalloc(); sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0); sqlite3EndBenignMalloc(); } WALTRACE(("WAL%p: closed\n", pWal)); sqlite3_free((void *)pWal->apWiData); sqlite3_free(pWal); } return rc; } /* ** Try to read the wal-index header. Return 0 on success and 1 if ** there is a problem. ** ** The wal-index is in shared memory. Another thread or process might ** be writing the header at the same time this procedure is trying to ** read it, which might result in inconsistency. A dirty read is detected ** by verifying that both copies of the header are the same and also by ** a checksum on the header. ** ** If and only if the read is consistent and the header is different from ** pWal->hdr, then pWal->hdr is updated to the content of the new header ** and *pChanged is set to 1. ** ** If the checksum cannot be verified return non-zero. If the header ** is read successfully and the checksum verified, return zero. */ static int walIndexTryHdr(Wal *pWal, int *pChanged){ u32 aCksum[2]; /* Checksum on the header content */ WalIndexHdr h1, h2; /* Two copies of the header content */ WalIndexHdr volatile *aHdr; /* Header in shared memory */ /* The first page of the wal-index must be mapped at this point. */ assert( pWal->nWiData>0 && pWal->apWiData[0] ); /* Read the header. This might happen concurrently with a write to the ** same area of shared memory on a different CPU in a SMP, ** meaning it is possible that an inconsistent snapshot is read ** from the file. If this happens, return non-zero. ** ** There are two copies of the header at the beginning of the wal-index. ** When reading, read [0] first then [1]. Writes are in the reverse order. ** Memory barriers are used to prevent the compiler or the hardware from ** reordering the reads and writes. */ aHdr = walIndexHdr(pWal); memcpy(&h1, (void *)&aHdr[0], sizeof(h1)); walShmBarrier(pWal); memcpy(&h2, (void *)&aHdr[1], sizeof(h2)); if( memcmp(&h1, &h2, sizeof(h1))!=0 ){ return 1; /* Dirty read */ } if( h1.isInit==0 ){ return 1; /* Malformed header - probably all zeros */ } walChecksumBytes(1, (u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum); if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){ return 1; /* Checksum does not match */ } if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){ *pChanged = 1; memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr)); pWal->szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16); testcase( pWal->szPage<=32768 ); testcase( pWal->szPage>=65536 ); } /* The header was successfully read. Return zero. */ return 0; } /* ** Read the wal-index header from the wal-index and into pWal->hdr. ** If the wal-header appears to be corrupt, try to reconstruct the ** wal-index from the WAL before returning. ** ** Set *pChanged to 1 if the wal-index header value in pWal->hdr is ** changed by this operation. If pWal->hdr is unchanged, set *pChanged ** to 0. ** ** If the wal-index header is successfully read, return SQLITE_OK. ** Otherwise an SQLite error code. */ static int walIndexReadHdr(Wal *pWal, int *pChanged){ int rc; /* Return code */ int badHdr; /* True if a header read failed */ volatile u32 *page0; /* Chunk of wal-index containing header */ /* Ensure that page 0 of the wal-index (the page that contains the ** wal-index header) is mapped. Return early if an error occurs here. */ assert( pChanged ); rc = walIndexPage(pWal, 0, &page0); if( rc!=SQLITE_OK ){ return rc; }; assert( page0 || pWal->writeLock==0 ); /* If the first page of the wal-index has been mapped, try to read the ** wal-index header immediately, without holding any lock. This usually ** works, but may fail if the wal-index header is corrupt or currently ** being modified by another thread or process. */ badHdr = (page0 ? walIndexTryHdr(pWal, pChanged) : 1); /* If the first attempt failed, it might have been due to a race ** with a writer. So get a WRITE lock and try again. */ assert( badHdr==0 || pWal->writeLock==0 ); if( badHdr ){ if( pWal->readOnly & WAL_SHM_RDONLY ){ if( SQLITE_OK==(rc = walLockShared(pWal, WAL_WRITE_LOCK)) ){ walUnlockShared(pWal, WAL_WRITE_LOCK); rc = SQLITE_READONLY_RECOVERY; } }else if( SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1)) ){ pWal->writeLock = 1; if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){ badHdr = walIndexTryHdr(pWal, pChanged); if( badHdr ){ /* If the wal-index header is still malformed even while holding ** a WRITE lock, it can only mean that the header is corrupted and ** needs to be reconstructed. So run recovery to do exactly that. */ rc = walIndexRecover(pWal); *pChanged = 1; } } pWal->writeLock = 0; walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); } } /* If the header is read successfully, check the version number to make ** sure the wal-index was not constructed with some future format that ** this version of SQLite cannot understand. */ if( badHdr==0 && pWal->hdr.iVersion!=WALINDEX_MAX_VERSION ){ rc = SQLITE_CANTOPEN_BKPT; } return rc; } /* ** This is the value that walTryBeginRead returns when it needs to ** be retried. */ #define WAL_RETRY (-1) /* ** Attempt to start a read transaction. This might fail due to a race or ** other transient condition. When that happens, it returns WAL_RETRY to ** indicate to the caller that it is safe to retry immediately. ** ** On success return SQLITE_OK. On a permanent failure (such an ** I/O error or an SQLITE_BUSY because another process is running ** recovery) return a positive error code. ** ** The useWal parameter is true to force the use of the WAL and disable ** the case where the WAL is bypassed because it has been completely ** checkpointed. If useWal==0 then this routine calls walIndexReadHdr() ** to make a copy of the wal-index header into pWal->hdr. If the ** wal-index header has changed, *pChanged is set to 1 (as an indication ** to the caller that the local paget cache is obsolete and needs to be ** flushed.) When useWal==1, the wal-index header is assumed to already ** be loaded and the pChanged parameter is unused. ** ** The caller must set the cnt parameter to the number of prior calls to ** this routine during the current read attempt that returned WAL_RETRY. ** This routine will start taking more aggressive measures to clear the ** race conditions after multiple WAL_RETRY returns, and after an excessive ** number of errors will ultimately return SQLITE_PROTOCOL. The ** SQLITE_PROTOCOL return indicates that some other process has gone rogue ** and is not honoring the locking protocol. There is a vanishingly small ** chance that SQLITE_PROTOCOL could be returned because of a run of really ** bad luck when there is lots of contention for the wal-index, but that ** possibility is so small that it can be safely neglected, we believe. ** ** On success, this routine obtains a read lock on ** WAL_READ_LOCK(pWal->readLock). The pWal->readLock integer is ** in the range 0 <= pWal->readLock < WAL_NREADER. If pWal->readLock==(-1) ** that means the Wal does not hold any read lock. The reader must not ** access any database page that is modified by a WAL frame up to and ** including frame number aReadMark[pWal->readLock]. The reader will ** use WAL frames up to and including pWal->hdr.mxFrame if pWal->readLock>0 ** Or if pWal->readLock==0, then the reader will ignore the WAL ** completely and get all content directly from the database file. ** If the useWal parameter is 1 then the WAL will never be ignored and ** this routine will always set pWal->readLock>0 on success. ** When the read transaction is completed, the caller must release the ** lock on WAL_READ_LOCK(pWal->readLock) and set pWal->readLock to -1. ** ** This routine uses the nBackfill and aReadMark[] fields of the header ** to select a particular WAL_READ_LOCK() that strives to let the ** checkpoint process do as much work as possible. This routine might ** update values of the aReadMark[] array in the header, but if it does ** so it takes care to hold an exclusive lock on the corresponding ** WAL_READ_LOCK() while changing values. */ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){ volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */ u32 mxReadMark; /* Largest aReadMark[] value */ int mxI; /* Index of largest aReadMark[] value */ int i; /* Loop counter */ int rc = SQLITE_OK; /* Return code */ u32 mxFrame; /* Wal frame to lock to */ assert( pWal->readLock<0 ); /* Not currently locked */ /* Take steps to avoid spinning forever if there is a protocol error. ** ** Circumstances that cause a RETRY should only last for the briefest ** instances of time. No I/O or other system calls are done while the ** locks are held, so the locks should not be held for very long. But ** if we are unlucky, another process that is holding a lock might get ** paged out or take a page-fault that is time-consuming to resolve, ** during the few nanoseconds that it is holding the lock. In that case, ** it might take longer than normal for the lock to free. ** ** After 5 RETRYs, we begin calling sqlite3OsSleep(). The first few ** calls to sqlite3OsSleep() have a delay of 1 microsecond. Really this ** is more of a scheduler yield than an actual delay. But on the 10th ** an subsequent retries, the delays start becoming longer and longer, ** so that on the 100th (and last) RETRY we delay for 323 milliseconds. ** The total delay time before giving up is less than 10 seconds. */ if( cnt>5 ){ int nDelay = 1; /* Pause time in microseconds */ if( cnt>100 ){ VVA_ONLY( pWal->lockError = 1; ) return SQLITE_PROTOCOL; } if( cnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39; sqlite3OsSleep(pWal->pVfs, nDelay); } if( !useWal ){ rc = walIndexReadHdr(pWal, pChanged); if( rc==SQLITE_BUSY ){ /* If there is not a recovery running in another thread or process ** then convert BUSY errors to WAL_RETRY. If recovery is known to ** be running, convert BUSY to BUSY_RECOVERY. There is a race here ** which might cause WAL_RETRY to be returned even if BUSY_RECOVERY ** would be technically correct. But the race is benign since with ** WAL_RETRY this routine will be called again and will probably be ** right on the second iteration. */ if( pWal->apWiData[0]==0 ){ /* This branch is taken when the xShmMap() method returns SQLITE_BUSY. ** We assume this is a transient condition, so return WAL_RETRY. The ** xShmMap() implementation used by the default unix and win32 VFS ** modules may return SQLITE_BUSY due to a race condition in the ** code that determines whether or not the shared-memory region ** must be zeroed before the requested page is returned. */ rc = WAL_RETRY; }else if( SQLITE_OK==(rc = walLockShared(pWal, WAL_RECOVER_LOCK)) ){ walUnlockShared(pWal, WAL_RECOVER_LOCK); rc = WAL_RETRY; }else if( rc==SQLITE_BUSY ){ rc = SQLITE_BUSY_RECOVERY; } } if( rc!=SQLITE_OK ){ return rc; } } pInfo = walCkptInfo(pWal); if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame #ifdef SQLITE_ENABLE_SNAPSHOT && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0 || 0==memcmp(&pWal->hdr, pWal->pSnapshot, sizeof(WalIndexHdr))) #endif ){ /* The WAL has been completely backfilled (or it is empty). ** and can be safely ignored. */ rc = walLockShared(pWal, WAL_READ_LOCK(0)); walShmBarrier(pWal); if( rc==SQLITE_OK ){ if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){ /* It is not safe to allow the reader to continue here if frames ** may have been appended to the log before READ_LOCK(0) was obtained. ** When holding READ_LOCK(0), the reader ignores the entire log file, ** which implies that the database file contains a trustworthy ** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from ** happening, this is usually correct. ** ** However, if frames have been appended to the log (or if the log ** is wrapped and written for that matter) before the READ_LOCK(0) ** is obtained, that is not necessarily true. A checkpointer may ** have started to backfill the appended frames but crashed before ** it finished. Leaving a corrupt image in the database file. */ walUnlockShared(pWal, WAL_READ_LOCK(0)); return WAL_RETRY; } pWal->readLock = 0; return SQLITE_OK; }else if( rc!=SQLITE_BUSY ){ return rc; } } /* If we get this far, it means that the reader will want to use ** the WAL to get at content from recent commits. The job now is ** to select one of the aReadMark[] entries that is closest to ** but not exceeding pWal->hdr.mxFrame and lock that entry. */ mxReadMark = 0; mxI = 0; mxFrame = pWal->hdr.mxFrame; #ifdef SQLITE_ENABLE_SNAPSHOT if( pWal->pSnapshot && pWal->pSnapshot->mxFramepSnapshot->mxFrame; } #endif for(i=1; iaReadMark[i]; if( mxReadMark<=thisMark && thisMark<=mxFrame ){ assert( thisMark!=READMARK_NOT_USED ); mxReadMark = thisMark; mxI = i; } } if( (pWal->readOnly & WAL_SHM_RDONLY)==0 && (mxReadMarkaReadMark[i] = mxFrame; mxI = i; walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); break; }else if( rc!=SQLITE_BUSY ){ return rc; } } } if( mxI==0 ){ assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 ); return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTLOCK; } rc = walLockShared(pWal, WAL_READ_LOCK(mxI)); if( rc ){ return rc==SQLITE_BUSY ? WAL_RETRY : rc; } /* Now that the read-lock has been obtained, check that neither the ** value in the aReadMark[] array or the contents of the wal-index ** header have changed. ** ** It is necessary to check that the wal-index header did not change ** between the time it was read and when the shared-lock was obtained ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility ** that the log file may have been wrapped by a writer, or that frames ** that occur later in the log than pWal->hdr.mxFrame may have been ** copied into the database by a checkpointer. If either of these things ** happened, then reading the database with the current value of ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry ** instead. ** ** Before checking that the live wal-index header has not changed ** since it was read, set Wal.minFrame to the first frame in the wal ** file that has not yet been checkpointed. This client will not need ** to read any frames earlier than minFrame from the wal file - they ** can be safely read directly from the database file. ** ** Because a ShmBarrier() call is made between taking the copy of ** nBackfill and checking that the wal-header in shared-memory still ** matches the one cached in pWal->hdr, it is guaranteed that the ** checkpointer that set nBackfill was not working with a wal-index ** header newer than that cached in pWal->hdr. If it were, that could ** cause a problem. The checkpointer could omit to checkpoint ** a version of page X that lies before pWal->minFrame (call that version ** A) on the basis that there is a newer version (version B) of the same ** page later in the wal file. But if version B happens to like past ** frame pWal->hdr.mxFrame - then the client would incorrectly assume ** that it can read version A from the database file. However, since ** we can guarantee that the checkpointer that set nBackfill could not ** see any pages past pWal->hdr.mxFrame, this problem does not come up. */ pWal->minFrame = pInfo->nBackfill+1; walShmBarrier(pWal); if( pInfo->aReadMark[mxI]!=mxReadMark || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){ walUnlockShared(pWal, WAL_READ_LOCK(mxI)); return WAL_RETRY; }else{ assert( mxReadMark<=pWal->hdr.mxFrame ); pWal->readLock = (i16)mxI; } return rc; } /* ** Begin a read transaction on the database. ** ** This routine used to be called sqlite3OpenSnapshot() and with good reason: ** it takes a snapshot of the state of the WAL and wal-index for the current ** instant in time. The current thread will continue to use this snapshot. ** Other threads might append new content to the WAL and wal-index but ** that extra content is ignored by the current thread. ** ** If the database contents have changes since the previous read ** transaction, then *pChanged is set to 1 before returning. The ** Pager layer will use this to know that is cache is stale and ** needs to be flushed. */ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){ int rc; /* Return code */ int cnt = 0; /* Number of TryBeginRead attempts */ #ifdef SQLITE_ENABLE_SNAPSHOT int bChanged = 0; WalIndexHdr *pSnapshot = pWal->pSnapshot; if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){ bChanged = 1; } #endif do{ rc = walTryBeginRead(pWal, pChanged, 0, ++cnt); }while( rc==WAL_RETRY ); testcase( (rc&0xff)==SQLITE_BUSY ); testcase( (rc&0xff)==SQLITE_IOERR ); testcase( rc==SQLITE_PROTOCOL ); testcase( rc==SQLITE_OK ); #ifdef SQLITE_ENABLE_SNAPSHOT if( rc==SQLITE_OK ){ if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){ /* At this point the client has a lock on an aReadMark[] slot holding ** a value equal to or smaller than pSnapshot->mxFrame, but pWal->hdr ** is populated with the wal-index header corresponding to the head ** of the wal file. Verify that pSnapshot is still valid before ** continuing. Reasons why pSnapshot might no longer be valid: ** ** (1) The WAL file has been reset since the snapshot was taken. ** In this case, the salt will have changed. ** ** (2) A checkpoint as been attempted that wrote frames past ** pSnapshot->mxFrame into the database file. Note that the ** checkpoint need not have completed for this to cause problems. */ volatile WalCkptInfo *pInfo = walCkptInfo(pWal); assert( pWal->readLock>0 || pWal->hdr.mxFrame==0 ); assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame ); /* It is possible that there is a checkpointer thread running ** concurrent with this code. If this is the case, it may be that the ** checkpointer has already determined that it will checkpoint ** snapshot X, where X is later in the wal file than pSnapshot, but ** has not yet set the pInfo->nBackfillAttempted variable to indicate ** its intent. To avoid the race condition this leads to, ensure that ** there is no checkpointer process by taking a shared CKPT lock ** before checking pInfo->nBackfillAttempted. */ rc = walLockShared(pWal, WAL_CKPT_LOCK); if( rc==SQLITE_OK ){ /* Check that the wal file has not been wrapped. Assuming that it has ** not, also check that no checkpointer has attempted to checkpoint any ** frames beyond pSnapshot->mxFrame. If either of these conditions are ** true, return SQLITE_BUSY_SNAPSHOT. Otherwise, overwrite pWal->hdr ** with *pSnapshot and set *pChanged as appropriate for opening the ** snapshot. */ if( !memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt)) && pSnapshot->mxFrame>=pInfo->nBackfillAttempted ){ assert( pWal->readLock>0 ); memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr)); *pChanged = bChanged; }else{ rc = SQLITE_BUSY_SNAPSHOT; } /* Release the shared CKPT lock obtained above. */ walUnlockShared(pWal, WAL_CKPT_LOCK); } if( rc!=SQLITE_OK ){ sqlite3WalEndReadTransaction(pWal); } } } #endif return rc; } /* ** Finish with a read transaction. All this does is release the ** read-lock. */ void sqlite3WalEndReadTransaction(Wal *pWal){ sqlite3WalEndWriteTransaction(pWal); if( pWal->readLock>=0 ){ walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock)); pWal->readLock = -1; } } /* ** Search the wal file for page pgno. If found, set *piRead to the frame that ** contains the page. Otherwise, if pgno is not in the wal file, set *piRead ** to zero. ** ** Return SQLITE_OK if successful, or an error code if an error occurs. If an ** error does occur, the final value of *piRead is undefined. */ int sqlite3WalFindFrame( Wal *pWal, /* WAL handle */ Pgno pgno, /* Database page number to read data for */ u32 *piRead /* OUT: Frame number (or zero) */ ){ u32 iRead = 0; /* If !=0, WAL frame to return data from */ u32 iLast = pWal->hdr.mxFrame; /* Last page in WAL for this reader */ int iHash; /* Used to loop through N hash tables */ int iMinHash; /* This routine is only be called from within a read transaction. */ assert( pWal->readLock>=0 || pWal->lockError ); /* If the "last page" field of the wal-index header snapshot is 0, then ** no data will be read from the wal under any circumstances. Return early ** in this case as an optimization. Likewise, if pWal->readLock==0, ** then the WAL is ignored by the reader so return early, as if the ** WAL were empty. */ if( iLast==0 || pWal->readLock==0 ){ *piRead = 0; return SQLITE_OK; } /* Search the hash table or tables for an entry matching page number ** pgno. Each iteration of the following for() loop searches one ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames). ** ** This code might run concurrently to the code in walIndexAppend() ** that adds entries to the wal-index (and possibly to this hash ** table). This means the value just read from the hash ** slot (aHash[iKey]) may have been added before or after the ** current read transaction was opened. Values added after the ** read transaction was opened may have been written incorrectly - ** i.e. these slots may contain garbage data. However, we assume ** that any slots written before the current read transaction was ** opened remain unmodified. ** ** For the reasons above, the if(...) condition featured in the inner ** loop of the following block is more stringent that would be required ** if we had exclusive access to the hash-table: ** ** (aPgno[iFrame]==pgno): ** This condition filters out normal hash-table collisions. ** ** (iFrame<=iLast): ** This condition filters out entries that were added to the hash ** table after the current read-transaction had started. */ iMinHash = walFramePage(pWal->minFrame); for(iHash=walFramePage(iLast); iHash>=iMinHash && iRead==0; iHash--){ volatile ht_slot *aHash; /* Pointer to hash table */ volatile u32 *aPgno; /* Pointer to array of page numbers */ u32 iZero; /* Frame number corresponding to aPgno[0] */ int iKey; /* Hash slot index */ int nCollide; /* Number of hash collisions remaining */ int rc; /* Error code */ rc = walHashGet(pWal, iHash, &aHash, &aPgno, &iZero); if( rc!=SQLITE_OK ){ return rc; } nCollide = HASHTABLE_NSLOT; for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){ u32 iFrame = aHash[iKey] + iZero; if( iFrame<=iLast && iFrame>=pWal->minFrame && aPgno[aHash[iKey]]==pgno ){ assert( iFrame>iRead || CORRUPT_DB ); iRead = iFrame; } if( (nCollide--)==0 ){ return SQLITE_CORRUPT_BKPT; } } } #ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT /* If expensive assert() statements are available, do a linear search ** of the wal-index file content. Make sure the results agree with the ** result obtained using the hash indexes above. */ { u32 iRead2 = 0; u32 iTest; assert( pWal->minFrame>0 ); for(iTest=iLast; iTest>=pWal->minFrame; iTest--){ if( walFramePgno(pWal, iTest)==pgno ){ iRead2 = iTest; break; } } assert( iRead==iRead2 ); } #endif *piRead = iRead; return SQLITE_OK; } /* ** Read the contents of frame iRead from the wal file into buffer pOut ** (which is nOut bytes in size). Return SQLITE_OK if successful, or an ** error code otherwise. */ int sqlite3WalReadFrame( Wal *pWal, /* WAL handle */ u32 iRead, /* Frame to read */ int nOut, /* Size of buffer pOut in bytes */ u8 *pOut /* Buffer to write page data to */ ){ int sz; i64 iOffset; sz = pWal->hdr.szPage; sz = (sz&0xfe00) + ((sz&0x0001)<<16); testcase( sz<=32768 ); testcase( sz>=65536 ); iOffset = walFrameOffset(iRead, sz) + WAL_FRAME_HDRSIZE; /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */ return sqlite3OsRead(pWal->pWalFd, pOut, (nOut>sz ? sz : nOut), iOffset); } /* ** Return the size of the database in pages (or zero, if unknown). */ Pgno sqlite3WalDbsize(Wal *pWal){ if( pWal && ALWAYS(pWal->readLock>=0) ){ return pWal->hdr.nPage; } return 0; } /* ** This function starts a write transaction on the WAL. ** ** A read transaction must have already been started by a prior call ** to sqlite3WalBeginReadTransaction(). ** ** If another thread or process has written into the database since ** the read transaction was started, then it is not possible for this ** thread to write as doing so would cause a fork. So this routine ** returns SQLITE_BUSY in that case and no write transaction is started. ** ** There can only be a single writer active at a time. */ int sqlite3WalBeginWriteTransaction(Wal *pWal){ int rc; /* Cannot start a write transaction without first holding a read ** transaction. */ assert( pWal->readLock>=0 ); assert( pWal->writeLock==0 && pWal->iReCksum==0 ); if( pWal->readOnly ){ return SQLITE_READONLY; } /* Only one writer allowed at a time. Get the write lock. Return ** SQLITE_BUSY if unable. */ rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1); if( rc ){ return rc; } pWal->writeLock = 1; /* If another connection has written to the database file since the ** time the read transaction on this connection was started, then ** the write is disallowed. */ if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){ walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); pWal->writeLock = 0; rc = SQLITE_BUSY_SNAPSHOT; } return rc; } /* ** End a write transaction. The commit has already been done. This ** routine merely releases the lock. */ int sqlite3WalEndWriteTransaction(Wal *pWal){ if( pWal->writeLock ){ walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); pWal->writeLock = 0; pWal->iReCksum = 0; pWal->truncateOnCommit = 0; } return SQLITE_OK; } /* ** If any data has been written (but not committed) to the log file, this ** function moves the write-pointer back to the start of the transaction. ** ** Additionally, the callback function is invoked for each frame written ** to the WAL since the start of the transaction. If the callback returns ** other than SQLITE_OK, it is not invoked again and the error code is ** returned to the caller. ** ** Otherwise, if the callback function does not return an error, this ** function returns SQLITE_OK. */ int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){ int rc = SQLITE_OK; if( ALWAYS(pWal->writeLock) ){ Pgno iMax = pWal->hdr.mxFrame; Pgno iFrame; /* Restore the clients cache of the wal-index header to the state it ** was in before the client began writing to the database. */ memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr)); for(iFrame=pWal->hdr.mxFrame+1; ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; iFrame++ ){ /* This call cannot fail. Unless the page for which the page number ** is passed as the second argument is (a) in the cache and ** (b) has an outstanding reference, then xUndo is either a no-op ** (if (a) is false) or simply expels the page from the cache (if (b) ** is false). ** ** If the upper layer is doing a rollback, it is guaranteed that there ** are no outstanding references to any page other than page 1. And ** page 1 is never written to the log until the transaction is ** committed. As a result, the call to xUndo may not fail. */ assert( walFramePgno(pWal, iFrame)!=1 ); rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame)); } if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal); } return rc; } /* ** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32 ** values. This function populates the array with values required to ** "rollback" the write position of the WAL handle back to the current ** point in the event of a savepoint rollback (via WalSavepointUndo()). */ void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData){ assert( pWal->writeLock ); aWalData[0] = pWal->hdr.mxFrame; aWalData[1] = pWal->hdr.aFrameCksum[0]; aWalData[2] = pWal->hdr.aFrameCksum[1]; aWalData[3] = pWal->nCkpt; } /* ** Move the write position of the WAL back to the point identified by ** the values in the aWalData[] array. aWalData must point to an array ** of WAL_SAVEPOINT_NDATA u32 values that has been previously populated ** by a call to WalSavepoint(). */ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){ int rc = SQLITE_OK; assert( pWal->writeLock ); assert( aWalData[3]!=pWal->nCkpt || aWalData[0]<=pWal->hdr.mxFrame ); if( aWalData[3]!=pWal->nCkpt ){ /* This savepoint was opened immediately after the write-transaction ** was started. Right after that, the writer decided to wrap around ** to the start of the log. Update the savepoint values to match. */ aWalData[0] = 0; aWalData[3] = pWal->nCkpt; } if( aWalData[0]hdr.mxFrame ){ pWal->hdr.mxFrame = aWalData[0]; pWal->hdr.aFrameCksum[0] = aWalData[1]; pWal->hdr.aFrameCksum[1] = aWalData[2]; walCleanupHash(pWal); } return rc; } /* ** This function is called just before writing a set of frames to the log ** file (see sqlite3WalFrames()). It checks to see if, instead of appending ** to the current log file, it is possible to overwrite the start of the ** existing log file with the new frames (i.e. "reset" the log). If so, ** it sets pWal->hdr.mxFrame to 0. Otherwise, pWal->hdr.mxFrame is left ** unchanged. ** ** SQLITE_OK is returned if no error is encountered (regardless of whether ** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned ** if an error occurs. */ static int walRestartLog(Wal *pWal){ int rc = SQLITE_OK; int cnt; if( pWal->readLock==0 ){ volatile WalCkptInfo *pInfo = walCkptInfo(pWal); assert( pInfo->nBackfill==pWal->hdr.mxFrame ); if( pInfo->nBackfill>0 ){ u32 salt1; sqlite3_randomness(4, &salt1); rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); if( rc==SQLITE_OK ){ /* If all readers are using WAL_READ_LOCK(0) (in other words if no ** readers are currently using the WAL), then the transactions ** frames will overwrite the start of the existing log. Update the ** wal-index header to reflect this. ** ** In theory it would be Ok to update the cache of the header only ** at this point. But updating the actual wal-index header is also ** safe and means there is no special case for sqlite3WalUndo() ** to handle if this transaction is rolled back. */ walRestartHdr(pWal, salt1); walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); }else if( rc!=SQLITE_BUSY ){ return rc; } } walUnlockShared(pWal, WAL_READ_LOCK(0)); pWal->readLock = -1; cnt = 0; do{ int notUsed; rc = walTryBeginRead(pWal, ¬Used, 1, ++cnt); }while( rc==WAL_RETRY ); assert( (rc&0xff)!=SQLITE_BUSY ); /* BUSY not possible when useWal==1 */ testcase( (rc&0xff)==SQLITE_IOERR ); testcase( rc==SQLITE_PROTOCOL ); testcase( rc==SQLITE_OK ); } return rc; } /* ** Information about the current state of the WAL file and where ** the next fsync should occur - passed from sqlite3WalFrames() into ** walWriteToLog(). */ typedef struct WalWriter { Wal *pWal; /* The complete WAL information */ sqlite3_file *pFd; /* The WAL file to which we write */ sqlite3_int64 iSyncPoint; /* Fsync at this offset */ int syncFlags; /* Flags for the fsync */ int szPage; /* Size of one page */ } WalWriter; /* ** Write iAmt bytes of content into the WAL file beginning at iOffset. ** Do a sync when crossing the p->iSyncPoint boundary. ** ** In other words, if iSyncPoint is in between iOffset and iOffset+iAmt, ** first write the part before iSyncPoint, then sync, then write the ** rest. */ static int walWriteToLog( WalWriter *p, /* WAL to write to */ void *pContent, /* Content to be written */ int iAmt, /* Number of bytes to write */ sqlite3_int64 iOffset /* Start writing at this offset */ ){ int rc; if( iOffsetiSyncPoint && iOffset+iAmt>=p->iSyncPoint ){ int iFirstAmt = (int)(p->iSyncPoint - iOffset); rc = sqlite3OsWrite(p->pFd, pContent, iFirstAmt, iOffset); if( rc ) return rc; iOffset += iFirstAmt; iAmt -= iFirstAmt; pContent = (void*)(iFirstAmt + (char*)pContent); assert( p->syncFlags & (SQLITE_SYNC_NORMAL|SQLITE_SYNC_FULL) ); rc = sqlite3OsSync(p->pFd, p->syncFlags & SQLITE_SYNC_MASK); if( iAmt==0 || rc ) return rc; } rc = sqlite3OsWrite(p->pFd, pContent, iAmt, iOffset); return rc; } /* ** Write out a single frame of the WAL */ static int walWriteOneFrame( WalWriter *p, /* Where to write the frame */ PgHdr *pPage, /* The page of the frame to be written */ int nTruncate, /* The commit flag. Usually 0. >0 for commit */ sqlite3_int64 iOffset /* Byte offset at which to write */ ){ int rc; /* Result code from subfunctions */ void *pData; /* Data actually written */ u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-header in */ #if defined(SQLITE_HAS_CODEC) if( (pData = sqlite3PagerCodec(pPage))==0 ) return SQLITE_NOMEM_BKPT; #else pData = pPage->pData; #endif walEncodeFrame(p->pWal, pPage->pgno, nTruncate, pData, aFrame); rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset); if( rc ) return rc; /* Write the page data */ rc = walWriteToLog(p, pData, p->szPage, iOffset+sizeof(aFrame)); return rc; } /* ** This function is called as part of committing a transaction within which ** one or more frames have been overwritten. It updates the checksums for ** all frames written to the wal file by the current transaction starting ** with the earliest to have been overwritten. ** ** SQLITE_OK is returned if successful, or an SQLite error code otherwise. */ static int walRewriteChecksums(Wal *pWal, u32 iLast){ const int szPage = pWal->szPage;/* Database page size */ int rc = SQLITE_OK; /* Return code */ u8 *aBuf; /* Buffer to load data from wal file into */ u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-headers in */ u32 iRead; /* Next frame to read from wal file */ i64 iCksumOff; aBuf = sqlite3_malloc(szPage + WAL_FRAME_HDRSIZE); if( aBuf==0 ) return SQLITE_NOMEM_BKPT; /* Find the checksum values to use as input for the recalculating the ** first checksum. If the first frame is frame 1 (implying that the current ** transaction restarted the wal file), these values must be read from the ** wal-file header. Otherwise, read them from the frame header of the ** previous frame. */ assert( pWal->iReCksum>0 ); if( pWal->iReCksum==1 ){ iCksumOff = 24; }else{ iCksumOff = walFrameOffset(pWal->iReCksum-1, szPage) + 16; } rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, iCksumOff); pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf); pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]); iRead = pWal->iReCksum; pWal->iReCksum = 0; for(; rc==SQLITE_OK && iRead<=iLast; iRead++){ i64 iOff = walFrameOffset(iRead, szPage); rc = sqlite3OsRead(pWal->pWalFd, aBuf, szPage+WAL_FRAME_HDRSIZE, iOff); if( rc==SQLITE_OK ){ u32 iPgno, nDbSize; iPgno = sqlite3Get4byte(aBuf); nDbSize = sqlite3Get4byte(&aBuf[4]); walEncodeFrame(pWal, iPgno, nDbSize, &aBuf[WAL_FRAME_HDRSIZE], aFrame); rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOff); } } sqlite3_free(aBuf); return rc; } /* ** Write a set of frames to the log. The caller must hold the write-lock ** on the log file (obtained using sqlite3WalBeginWriteTransaction()). */ int sqlite3WalFrames( Wal *pWal, /* Wal handle to write to */ int szPage, /* Database page-size in bytes */ PgHdr *pList, /* List of dirty pages to write */ Pgno nTruncate, /* Database size after this commit */ int isCommit, /* True if this is a commit */ int sync_flags /* Flags to pass to OsSync() (or 0) */ ){ int rc; /* Used to catch return codes */ u32 iFrame; /* Next frame address */ PgHdr *p; /* Iterator to run through pList with. */ PgHdr *pLast = 0; /* Last frame in list */ int nExtra = 0; /* Number of extra copies of last page */ int szFrame; /* The size of a single frame */ i64 iOffset; /* Next byte to write in WAL file */ WalWriter w; /* The writer */ u32 iFirst = 0; /* First frame that may be overwritten */ WalIndexHdr *pLive; /* Pointer to shared header */ assert( pList ); assert( pWal->writeLock ); /* If this frame set completes a transaction, then nTruncate>0. If ** nTruncate==0 then this frame set does not complete the transaction. */ assert( (isCommit!=0)==(nTruncate!=0) ); #if defined(SQLITE_TEST) && defined(SQLITE_DEBUG) { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){} WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n", pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill")); } #endif pLive = (WalIndexHdr*)walIndexHdr(pWal); if( memcmp(&pWal->hdr, (void *)pLive, sizeof(WalIndexHdr))!=0 ){ iFirst = pLive->mxFrame+1; } /* See if it is possible to write these frames into the start of the ** log file, instead of appending to it at pWal->hdr.mxFrame. */ if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){ return rc; } /* If this is the first frame written into the log, write the WAL ** header to the start of the WAL file. See comments at the top of ** this source file for a description of the WAL header format. */ iFrame = pWal->hdr.mxFrame; if( iFrame==0 ){ u8 aWalHdr[WAL_HDRSIZE]; /* Buffer to assemble wal-header in */ u32 aCksum[2]; /* Checksum for wal-header */ sqlite3Put4byte(&aWalHdr[0], (WAL_MAGIC | SQLITE_BIGENDIAN)); sqlite3Put4byte(&aWalHdr[4], WAL_MAX_VERSION); sqlite3Put4byte(&aWalHdr[8], szPage); sqlite3Put4byte(&aWalHdr[12], pWal->nCkpt); if( pWal->nCkpt==0 ) sqlite3_randomness(8, pWal->hdr.aSalt); memcpy(&aWalHdr[16], pWal->hdr.aSalt, 8); walChecksumBytes(1, aWalHdr, WAL_HDRSIZE-2*4, 0, aCksum); sqlite3Put4byte(&aWalHdr[24], aCksum[0]); sqlite3Put4byte(&aWalHdr[28], aCksum[1]); pWal->szPage = szPage; pWal->hdr.bigEndCksum = SQLITE_BIGENDIAN; pWal->hdr.aFrameCksum[0] = aCksum[0]; pWal->hdr.aFrameCksum[1] = aCksum[1]; pWal->truncateOnCommit = 1; rc = sqlite3OsWrite(pWal->pWalFd, aWalHdr, sizeof(aWalHdr), 0); WALTRACE(("WAL%p: wal-header write %s\n", pWal, rc ? "failed" : "ok")); if( rc!=SQLITE_OK ){ return rc; } /* Sync the header (unless SQLITE_IOCAP_SEQUENTIAL is true or unless ** all syncing is turned off by PRAGMA synchronous=OFF). Otherwise ** an out-of-order write following a WAL restart could result in ** database corruption. See the ticket: ** ** http://localhost:591/sqlite/info/ff5be73dee */ if( pWal->syncHeader && sync_flags ){ rc = sqlite3OsSync(pWal->pWalFd, sync_flags & SQLITE_SYNC_MASK); if( rc ) return rc; } } assert( (int)pWal->szPage==szPage ); /* Setup information needed to write frames into the WAL */ w.pWal = pWal; w.pFd = pWal->pWalFd; w.iSyncPoint = 0; w.syncFlags = sync_flags; w.szPage = szPage; iOffset = walFrameOffset(iFrame+1, szPage); szFrame = szPage + WAL_FRAME_HDRSIZE; /* Write all frames into the log file exactly once */ for(p=pList; p; p=p->pDirty){ int nDbSize; /* 0 normally. Positive == commit flag */ /* Check if this page has already been written into the wal file by ** the current transaction. If so, overwrite the existing frame and ** set Wal.writeLock to WAL_WRITELOCK_RECKSUM - indicating that ** checksums must be recomputed when the transaction is committed. */ if( iFirst && (p->pDirty || isCommit==0) ){ u32 iWrite = 0; VVA_ONLY(rc =) sqlite3WalFindFrame(pWal, p->pgno, &iWrite); assert( rc==SQLITE_OK || iWrite==0 ); if( iWrite>=iFirst ){ i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE; void *pData; if( pWal->iReCksum==0 || iWriteiReCksum ){ pWal->iReCksum = iWrite; } #if defined(SQLITE_HAS_CODEC) if( (pData = sqlite3PagerCodec(p))==0 ) return SQLITE_NOMEM; #else pData = p->pData; #endif rc = sqlite3OsWrite(pWal->pWalFd, pData, szPage, iOff); if( rc ) return rc; p->flags &= ~PGHDR_WAL_APPEND; continue; } } iFrame++; assert( iOffset==walFrameOffset(iFrame, szPage) ); nDbSize = (isCommit && p->pDirty==0) ? nTruncate : 0; rc = walWriteOneFrame(&w, p, nDbSize, iOffset); if( rc ) return rc; pLast = p; iOffset += szFrame; p->flags |= PGHDR_WAL_APPEND; } /* Recalculate checksums within the wal file if required. */ if( isCommit && pWal->iReCksum ){ rc = walRewriteChecksums(pWal, iFrame); if( rc ) return rc; } /* If this is the end of a transaction, then we might need to pad ** the transaction and/or sync the WAL file. ** ** Padding and syncing only occur if this set of frames complete a ** transaction and if PRAGMA synchronous=FULL. If synchronous==NORMAL ** or synchronous==OFF, then no padding or syncing are needed. ** ** If SQLITE_IOCAP_POWERSAFE_OVERWRITE is defined, then padding is not ** needed and only the sync is done. If padding is needed, then the ** final frame is repeated (with its commit mark) until the next sector ** boundary is crossed. Only the part of the WAL prior to the last ** sector boundary is synced; the part of the last frame that extends ** past the sector boundary is written after the sync. */ if( isCommit && (sync_flags & WAL_SYNC_TRANSACTIONS)!=0 ){ if( pWal->padToSectorBoundary ){ int sectorSize = sqlite3SectorSize(pWal->pWalFd); w.iSyncPoint = ((iOffset+sectorSize-1)/sectorSize)*sectorSize; while( iOffsettruncateOnCommit && pWal->mxWalSize>=0 ){ i64 sz = pWal->mxWalSize; if( walFrameOffset(iFrame+nExtra+1, szPage)>pWal->mxWalSize ){ sz = walFrameOffset(iFrame+nExtra+1, szPage); } walLimitSize(pWal, sz); pWal->truncateOnCommit = 0; } /* Append data to the wal-index. It is not necessary to lock the ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index ** guarantees that there are no other writers, and no data that may ** be in use by existing readers is being overwritten. */ iFrame = pWal->hdr.mxFrame; for(p=pList; p && rc==SQLITE_OK; p=p->pDirty){ if( (p->flags & PGHDR_WAL_APPEND)==0 ) continue; iFrame++; rc = walIndexAppend(pWal, iFrame, p->pgno); } while( rc==SQLITE_OK && nExtra>0 ){ iFrame++; nExtra--; rc = walIndexAppend(pWal, iFrame, pLast->pgno); } if( rc==SQLITE_OK ){ /* Update the private copy of the header. */ pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16)); testcase( szPage<=32768 ); testcase( szPage>=65536 ); pWal->hdr.mxFrame = iFrame; if( isCommit ){ pWal->hdr.iChange++; pWal->hdr.nPage = nTruncate; } /* If this is a commit, update the wal-index header too. */ if( isCommit ){ walIndexWriteHdr(pWal); pWal->iCallback = iFrame; } } WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok")); return rc; } /* ** This routine is called to implement sqlite3_wal_checkpoint() and ** related interfaces. ** ** Obtain a CHECKPOINT lock and then backfill as much information as ** we can from WAL into the database. ** ** If parameter xBusy is not NULL, it is a pointer to a busy-handler ** callback. In this case this function runs a blocking checkpoint. */ int sqlite3WalCheckpoint( Wal *pWal, /* Wal connection */ int eMode, /* PASSIVE, FULL, RESTART, or TRUNCATE */ int (*xBusy)(void*), /* Function to call when busy */ void *pBusyArg, /* Context argument for xBusyHandler */ int sync_flags, /* Flags to sync db file with (or 0) */ int nBuf, /* Size of temporary buffer */ u8 *zBuf, /* Temporary buffer to use */ int *pnLog, /* OUT: Number of frames in WAL */ int *pnCkpt /* OUT: Number of backfilled frames in WAL */ ){ int rc; /* Return code */ int isChanged = 0; /* True if a new wal-index header is loaded */ int eMode2 = eMode; /* Mode to pass to walCheckpoint() */ int (*xBusy2)(void*) = xBusy; /* Busy handler for eMode2 */ assert( pWal->ckptLock==0 ); assert( pWal->writeLock==0 ); /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked ** in the SQLITE_CHECKPOINT_PASSIVE mode. */ assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 ); if( pWal->readOnly ) return SQLITE_READONLY; WALTRACE(("WAL%p: checkpoint begins\n", pWal)); /* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive ** "checkpoint" lock on the database file. */ rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1); if( rc ){ /* EVIDENCE-OF: R-10421-19736 If any other process is running a ** checkpoint operation at the same time, the lock cannot be obtained and ** SQLITE_BUSY is returned. ** EVIDENCE-OF: R-53820-33897 Even if there is a busy-handler configured, ** it will not be invoked in this case. */ testcase( rc==SQLITE_BUSY ); testcase( xBusy!=0 ); return rc; } pWal->ckptLock = 1; /* IMPLEMENTATION-OF: R-59782-36818 The SQLITE_CHECKPOINT_FULL, RESTART and ** TRUNCATE modes also obtain the exclusive "writer" lock on the database ** file. ** ** EVIDENCE-OF: R-60642-04082 If the writer lock cannot be obtained ** immediately, and a busy-handler is configured, it is invoked and the ** writer lock retried until either the busy-handler returns 0 or the ** lock is successfully obtained. */ if( eMode!=SQLITE_CHECKPOINT_PASSIVE ){ rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_WRITE_LOCK, 1); if( rc==SQLITE_OK ){ pWal->writeLock = 1; }else if( rc==SQLITE_BUSY ){ eMode2 = SQLITE_CHECKPOINT_PASSIVE; xBusy2 = 0; rc = SQLITE_OK; } } /* Read the wal-index header. */ if( rc==SQLITE_OK ){ rc = walIndexReadHdr(pWal, &isChanged); if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){ sqlite3OsUnfetch(pWal->pDbFd, 0, 0); } } /* Copy data from the log to the database file. */ if( rc==SQLITE_OK ){ if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){ rc = SQLITE_CORRUPT_BKPT; }else{ rc = walCheckpoint(pWal, eMode2, xBusy2, pBusyArg, sync_flags, zBuf); } /* If no error occurred, set the output variables. */ if( rc==SQLITE_OK || rc==SQLITE_BUSY ){ if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame; if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill); } } if( isChanged ){ /* If a new wal-index header was loaded before the checkpoint was ** performed, then the pager-cache associated with pWal is now ** out of date. So zero the cached wal-index header to ensure that ** next time the pager opens a snapshot on this database it knows that ** the cache needs to be reset. */ memset(&pWal->hdr, 0, sizeof(WalIndexHdr)); } /* Release the locks. */ sqlite3WalEndWriteTransaction(pWal); walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1); pWal->ckptLock = 0; WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok")); return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc); } /* Return the value to pass to a sqlite3_wal_hook callback, the ** number of frames in the WAL at the point of the last commit since ** sqlite3WalCallback() was called. If no commits have occurred since ** the last call, then return 0. */ int sqlite3WalCallback(Wal *pWal){ u32 ret = 0; if( pWal ){ ret = pWal->iCallback; pWal->iCallback = 0; } return (int)ret; } /* ** This function is called to change the WAL subsystem into or out ** of locking_mode=EXCLUSIVE. ** ** If op is zero, then attempt to change from locking_mode=EXCLUSIVE ** into locking_mode=NORMAL. This means that we must acquire a lock ** on the pWal->readLock byte. If the WAL is already in locking_mode=NORMAL ** or if the acquisition of the lock fails, then return 0. If the ** transition out of exclusive-mode is successful, return 1. This ** operation must occur while the pager is still holding the exclusive ** lock on the main database file. ** ** If op is one, then change from locking_mode=NORMAL into ** locking_mode=EXCLUSIVE. This means that the pWal->readLock must ** be released. Return 1 if the transition is made and 0 if the ** WAL is already in exclusive-locking mode - meaning that this ** routine is a no-op. The pager must already hold the exclusive lock ** on the main database file before invoking this operation. ** ** If op is negative, then do a dry-run of the op==1 case but do ** not actually change anything. The pager uses this to see if it ** should acquire the database exclusive lock prior to invoking ** the op==1 case. */ int sqlite3WalExclusiveMode(Wal *pWal, int op){ int rc; assert( pWal->writeLock==0 ); assert( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE || op==-1 ); /* pWal->readLock is usually set, but might be -1 if there was a ** prior error while attempting to acquire are read-lock. This cannot ** happen if the connection is actually in exclusive mode (as no xShmLock ** locks are taken in this case). Nor should the pager attempt to ** upgrade to exclusive-mode following such an error. */ assert( pWal->readLock>=0 || pWal->lockError ); assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) ); if( op==0 ){ if( pWal->exclusiveMode ){ pWal->exclusiveMode = 0; if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){ pWal->exclusiveMode = 1; } rc = pWal->exclusiveMode==0; }else{ /* Already in locking_mode=NORMAL */ rc = 0; } }else if( op>0 ){ assert( pWal->exclusiveMode==0 ); assert( pWal->readLock>=0 ); walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock)); pWal->exclusiveMode = 1; rc = 1; }else{ rc = pWal->exclusiveMode==0; } return rc; } /* ** Return true if the argument is non-NULL and the WAL module is using ** heap-memory for the wal-index. Otherwise, if the argument is NULL or the ** WAL module is using shared-memory, return false. */ int sqlite3WalHeapMemory(Wal *pWal){ return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ); } #ifdef SQLITE_ENABLE_SNAPSHOT /* Create a snapshot object. The content of a snapshot is opaque to ** every other subsystem, so the WAL module can put whatever it needs ** in the object. */ int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){ int rc = SQLITE_OK; WalIndexHdr *pRet; assert( pWal->readLock>=0 && pWal->writeLock==0 ); pRet = (WalIndexHdr*)sqlite3_malloc(sizeof(WalIndexHdr)); if( pRet==0 ){ rc = SQLITE_NOMEM_BKPT; }else{ memcpy(pRet, &pWal->hdr, sizeof(WalIndexHdr)); *ppSnapshot = (sqlite3_snapshot*)pRet; } return rc; } /* Try to open on pSnapshot when the next read-transaction starts */ void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot){ pWal->pSnapshot = (WalIndexHdr*)pSnapshot; } /* ** Return a +ve value if snapshot p1 is newer than p2. A -ve value if ** p1 is older than p2 and zero if p1 and p2 are the same snapshot. */ int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){ WalIndexHdr *pHdr1 = (WalIndexHdr*)p1; WalIndexHdr *pHdr2 = (WalIndexHdr*)p2; /* aSalt[0] is a copy of the value stored in the wal file header. It ** is incremented each time the wal file is restarted. */ if( pHdr1->aSalt[0]aSalt[0] ) return -1; if( pHdr1->aSalt[0]>pHdr2->aSalt[0] ) return +1; if( pHdr1->mxFramemxFrame ) return -1; if( pHdr1->mxFrame>pHdr2->mxFrame ) return +1; return 0; } #endif /* SQLITE_ENABLE_SNAPSHOT */ #ifdef SQLITE_ENABLE_ZIPVFS /* ** If the argument is not NULL, it points to a Wal object that holds a ** read-lock. This function returns the database page-size if it is known, ** or zero if it is not (or if pWal is NULL). */ int sqlite3WalFramesize(Wal *pWal){ assert( pWal==0 || pWal->readLock>=0 ); return (pWal ? pWal->szPage : 0); } #endif /* Return the sqlite3_file object for the WAL file */ sqlite3_file *sqlite3WalFile(Wal *pWal){ return pWal->pWalFd; } #endif /* #ifndef SQLITE_OMIT_WAL */