/*
** 2001 September 15
**
** 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 is the implementation of the page cache subsystem or "pager".
**
** The pager is used to access a database disk file. It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file. The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.47 2002/06/25 14:43:58 drh Exp $
*/
#include "sqliteInt.h"
#include "pager.h"
#include "os.h"
#include <assert.h>
#include <string.h>
/*
** The page cache as a whole is always in one of the following
** states:
**
** SQLITE_UNLOCK The page cache is not currently reading or
** writing the database file. There is no
** data held in memory. This is the initial
** state.
**
** SQLITE_READLOCK The page cache is reading the database.
** Writing is not permitted. There can be
** multiple readers accessing the same database
** file at the same time.
**
** SQLITE_WRITELOCK The page cache is writing the database.
** Access is exclusive. No other processes or
** threads can be reading or writing while one
** process is writing.
**
** The page cache comes up in SQLITE_UNLOCK. The first time a
** sqlite_page_get() occurs, the state transitions to SQLITE_READLOCK.
** After all pages have been released using sqlite_page_unref(),
** the state transitions back to SQLITE_UNLOCK. The first time
** that sqlite_page_write() is called, the state transitions to
** SQLITE_WRITELOCK. (Note that sqlite_page_write() can only be
** called on an outstanding page which means that the pager must
** be in SQLITE_READLOCK before it transitions to SQLITE_WRITELOCK.)
** The sqlite_page_rollback() and sqlite_page_commit() functions
** transition the state from SQLITE_WRITELOCK back to SQLITE_READLOCK.
*/
#define SQLITE_UNLOCK 0
#define SQLITE_READLOCK 1
#define SQLITE_WRITELOCK 2
/*
** Each in-memory image of a page begins with the following header.
** This header is only visible to this pager module. The client
** code that calls pager sees only the data that follows the header.
*/
typedef struct PgHdr PgHdr;
struct PgHdr {
Pager *pPager; /* The pager to which this page belongs */
Pgno pgno; /* The page number for this page */
PgHdr *pNextHash, *pPrevHash; /* Hash collision chain for PgHdr.pgno */
int nRef; /* Number of users of this page */
PgHdr *pNextFree, *pPrevFree; /* Freelist of pages where nRef==0 */
PgHdr *pNextAll, *pPrevAll; /* A list of all pages */
char inJournal; /* TRUE if has been written to journal */
char inCkpt; /* TRUE if written to the checkpoint journal */
char dirty; /* TRUE if we need to write back changes */
/* SQLITE_PAGE_SIZE bytes of page data follow this header */
/* Pager.nExtra bytes of local data follow the page data */
};
/*
** Convert a pointer to a PgHdr into a pointer to its data
** and back again.
*/
#define PGHDR_TO_DATA(P) ((void*)(&(P)[1]))
#define DATA_TO_PGHDR(D) (&((PgHdr*)(D))[-1])
#define PGHDR_TO_EXTRA(P) ((void*)&((char*)(&(P)[1]))[SQLITE_PAGE_SIZE])
/*
** How big to make the hash table used for locating in-memory pages
** by page number. Knuth says this should be a prime number.
*/
#define N_PG_HASH 2003
/*
** A open page cache is an instance of the following structure.
*/
struct Pager {
char *zFilename; /* Name of the database file */
char *zJournal; /* Name of the journal file */
OsFile fd, jfd; /* File descriptors for database and journal */
OsFile cpfd; /* File descriptor for the checkpoint journal */
int dbSize; /* Number of pages in the file */
int origDbSize; /* dbSize before the current change */
int ckptSize, ckptJSize; /* Size of database and journal at ckpt_begin() */
int nExtra; /* Add this many bytes to each in-memory page */
void (*xDestructor)(void*); /* Call this routine when freeing pages */
int nPage; /* Total number of in-memory pages */
int nRef; /* Number of in-memory pages with PgHdr.nRef>0 */
int mxPage; /* Maximum number of pages to hold in cache */
int nHit, nMiss, nOvfl; /* Cache hits, missing, and LRU overflows */
u8 journalOpen; /* True if journal file descriptors is valid */
u8 ckptOpen; /* True if the checkpoint journal is open */
u8 ckptInUse; /* True we are in a checkpoint */
u8 noSync; /* Do not sync the journal if true */
u8 state; /* SQLITE_UNLOCK, _READLOCK or _WRITELOCK */
u8 errMask; /* One of several kinds of errors */
u8 tempFile; /* zFilename is a temporary file */
u8 readOnly; /* True for a read-only database */
u8 needSync; /* True if an fsync() is needed on the journal */
u8 dirtyFile; /* True if database file has changed in any way */
u8 *aInJournal; /* One bit for each page in the database file */
u8 *aInCkpt; /* One bit for each page in the database */
PgHdr *pFirst, *pLast; /* List of free pages */
PgHdr *pAll; /* List of all pages */
PgHdr *aHash[N_PG_HASH]; /* Hash table to map page number of PgHdr */
};
/*
** These are bits that can be set in Pager.errMask.
*/
#define PAGER_ERR_FULL 0x01 /* a write() failed */
#define PAGER_ERR_MEM 0x02 /* malloc() failed */
#define PAGER_ERR_LOCK 0x04 /* error in the locking protocol */
#define PAGER_ERR_CORRUPT 0x08 /* database or journal corruption */
#define PAGER_ERR_DISK 0x10 /* general disk I/O error - bad hard drive? */
/*
** The journal file contains page records in the following
** format.
*/
typedef struct PageRecord PageRecord;
struct PageRecord {
Pgno pgno; /* The page number */
char aData[SQLITE_PAGE_SIZE]; /* Original data for page pgno */
};
/*
** Journal files begin with the following magic string. The data
** was obtained from /dev/random. It is used only as a sanity check.
*/
static const unsigned char aJournalMagic[] = {
0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd4,
};
/*
** Hash a page number
*/
#define pager_hash(PN) ((PN)%N_PG_HASH)
/*
** Enable reference count tracking here:
*/
#if SQLITE_TEST
int pager_refinfo_enable = 0;
static void pager_refinfo(PgHdr *p){
static int cnt = 0;
if( !pager_refinfo_enable ) return;
printf(
"REFCNT: %4d addr=0x%08x nRef=%d\n",
p->pgno, (int)PGHDR_TO_DATA(p), p->nRef
);
cnt++; /* Something to set a breakpoint on */
}
# define REFINFO(X) pager_refinfo(X)
#else
# define REFINFO(X)
#endif
/*
** Convert the bits in the pPager->errMask into an approprate
** return code.
*/
static int pager_errcode(Pager *pPager){
int rc = SQLITE_OK;
if( pPager->errMask & PAGER_ERR_LOCK ) rc = SQLITE_PROTOCOL;
if( pPager->errMask & PAGER_ERR_DISK ) rc = SQLITE_IOERR;
if( pPager->errMask & PAGER_ERR_FULL ) rc = SQLITE_FULL;
if( pPager->errMask & PAGER_ERR_MEM ) rc = SQLITE_NOMEM;
if( pPager->errMask & PAGER_ERR_CORRUPT ) rc = SQLITE_CORRUPT;
return rc;
}
/*
** Find a page in the hash table given its page number. Return
** a pointer to the page or NULL if not found.
*/
static PgHdr *pager_lookup(Pager *pPager, Pgno pgno){
PgHdr *p = pPager->aHash[pgno % N_PG_HASH];
while( p && p->pgno!=pgno ){
p = p->pNextHash;
}
return p;
}
/*
** Unlock the database and clear the in-memory cache. This routine
** sets the state of the pager back to what it was when it was first
** opened. Any outstanding pages are invalidated and subsequent attempts
** to access those pages will likely result in a coredump.
*/
static void pager_reset(Pager *pPager){
PgHdr *pPg, *pNext;
for(pPg=pPager->pAll; pPg; pPg=pNext){
pNext = pPg->pNextAll;
sqliteFree(pPg);
}
pPager->pFirst = 0;
pPager->pLast = 0;
pPager->pAll = 0;
memset(pPager->aHash, 0, sizeof(pPager->aHash));
pPager->nPage = 0;
if( pPager->state>=SQLITE_WRITELOCK ){
sqlitepager_rollback(pPager);
}
sqliteOsUnlock(&pPager->fd);
pPager->state = SQLITE_UNLOCK;
pPager->dbSize = -1;
pPager->nRef = 0;
assert( pPager->journalOpen==0 );
}
/*
** When this routine is called, the pager has the journal file open and
** a write lock on the database. This routine releases the database
** write lock and acquires a read lock in its place. The journal file
** is deleted and closed.
*/
static int pager_unwritelock(Pager *pPager){
int rc;
PgHdr *pPg;
if( pPager->state<SQLITE_WRITELOCK ) return SQLITE_OK;
sqlitepager_ckpt_commit(pPager);
if( pPager->ckptOpen ){
sqliteOsClose(&pPager->cpfd);
pPager->ckptOpen = 0;
}
sqliteOsClose(&pPager->jfd);
pPager->journalOpen = 0;
sqliteOsDelete(pPager->zJournal);
rc = sqliteOsReadLock(&pPager->fd);
assert( rc==SQLITE_OK );
sqliteFree( pPager->aInJournal );
pPager->aInJournal = 0;
for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
pPg->inJournal = 0;
pPg->dirty = 0;
}
pPager->state = SQLITE_READLOCK;
return rc;
}
/*
** Read a single page from the journal file opened on file descriptor
** jfd. Playback this one page.
*/
static int pager_playback_one_page(Pager *pPager, OsFile *jfd){
int rc;
PgHdr *pPg; /* An existing page in the cache */
PageRecord pgRec;
rc = sqliteOsRead(jfd, &pgRec, sizeof(pgRec));
if( rc!=SQLITE_OK ) return rc;
/* Sanity checking on the page */
if( pgRec.pgno>pPager->dbSize || pgRec.pgno==0 ) return SQLITE_CORRUPT;
/* Playback the page. Update the in-memory copy of the page
** at the same time, if there is one.
*/
pPg = pager_lookup(pPager, pgRec.pgno);
if( pPg ){
memcpy(PGHDR_TO_DATA(pPg), pgRec.aData, SQLITE_PAGE_SIZE);
memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
}
rc = sqliteOsSeek(&pPager->fd, (pgRec.pgno-1)*SQLITE_PAGE_SIZE);
if( rc==SQLITE_OK ){
rc = sqliteOsWrite(&pPager->fd, pgRec.aData, SQLITE_PAGE_SIZE);
}
return rc;
}
/*
** Playback the journal and thus restore the database file to
** the state it was in before we started making changes.
**
** The journal file format is as follows: There is an initial
** file-type string for sanity checking. Then there is a single
** Pgno number which is the number of pages in the database before
** changes were made. The database is truncated to this size.
** Next come zero or more page records where each page record
** consists of a Pgno and SQLITE_PAGE_SIZE bytes of data. See
** the PageRecord structure for details.
**
** If the file opened as the journal file is not a well-formed
** journal file (as determined by looking at the magic number
** at the beginning) then this routine returns SQLITE_PROTOCOL.
** If any other errors occur during playback, the database will
** likely be corrupted, so the PAGER_ERR_CORRUPT bit is set in
** pPager->errMask and SQLITE_CORRUPT is returned. If it all
** works, then this routine returns SQLITE_OK.
*/
static int pager_playback(Pager *pPager){
int nRec; /* Number of Records */
int i; /* Loop counter */
Pgno mxPg = 0; /* Size of the original file in pages */
unsigned char aMagic[sizeof(aJournalMagic)];
int rc;
/* Figure out how many records are in the journal. Abort early if
** the journal is empty.
*/
assert( pPager->journalOpen );
sqliteOsSeek(&pPager->jfd, 0);
rc = sqliteOsFileSize(&pPager->jfd, &nRec);
if( rc!=SQLITE_OK ){
goto end_playback;
}
nRec = (nRec - (sizeof(aMagic)+sizeof(Pgno))) / sizeof(PageRecord);
if( nRec<=0 ){
goto end_playback;
}
/* Read the beginning of the journal and truncate the
** database file back to its original size.
*/
rc = sqliteOsRead(&pPager->jfd, aMagic, sizeof(aMagic));
if( rc!=SQLITE_OK || memcmp(aMagic,aJournalMagic,sizeof(aMagic))!=0 ){
rc = SQLITE_PROTOCOL;
goto end_playback;
}
rc = sqliteOsRead(&pPager->jfd, &mxPg, sizeof(mxPg));
if( rc!=SQLITE_OK ){
goto end_playback;
}
rc = sqliteOsTruncate(&pPager->fd, mxPg*SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ){
goto end_playback;
}
pPager->dbSize = mxPg;
/* Copy original pages out of the journal and back into the database file.
*/
for(i=nRec-1; i>=0; i--){
rc = pager_playback_one_page(pPager, &pPager->jfd);
if( rc!=SQLITE_OK ) break;
}
end_playback:
if( rc!=SQLITE_OK ){
pager_unwritelock(pPager);
pPager->errMask |= PAGER_ERR_CORRUPT;
rc = SQLITE_CORRUPT;
}else{
rc = pager_unwritelock(pPager);
}
return rc;
}
/*
** Playback the checkpoint journal.
**
** This is similar to playing back the transaction journal but with
** a few extra twists.
**
** (1) The number of pages in the database file at the start of
** the checkpoint is stored in pPager->ckptSize, not in the
** journal file itself.
**
** (2) In addition to playing back the checkpoint journal, also
** playback all pages of the transaction journal beginning
** at offset pPager->ckptJSize.
*/
static int pager_ckpt_playback(Pager *pPager){
int nRec; /* Number of Records */
int i; /* Loop counter */
int rc;
/* Truncate the database back to its original size.
*/
rc = sqliteOsTruncate(&pPager->fd, pPager->ckptSize*SQLITE_PAGE_SIZE);
pPager->dbSize = pPager->ckptSize;
/* Figure out how many records are in the checkpoint journal.
*/
assert( pPager->ckptInUse && pPager->journalOpen );
sqliteOsSeek(&pPager->cpfd, 0);
rc = sqliteOsFileSize(&pPager->cpfd, &nRec);
if( rc!=SQLITE_OK ){
goto end_ckpt_playback;
}
nRec /= sizeof(PageRecord);
/* Copy original pages out of the checkpoint journal and back into the
** database file.
*/
for(i=nRec-1; i>=0; i--){
rc = pager_playback_one_page(pPager, &pPager->cpfd);
if( rc!=SQLITE_OK ) goto end_ckpt_playback;
}
/* Figure out how many pages need to be copied out of the transaction
** journal.
*/
rc = sqliteOsSeek(&pPager->jfd, pPager->ckptJSize);
if( rc!=SQLITE_OK ){
goto end_ckpt_playback;
}
rc = sqliteOsFileSize(&pPager->jfd, &nRec);
if( rc!=SQLITE_OK ){
goto end_ckpt_playback;
}
nRec = (nRec - pPager->ckptJSize)/sizeof(PageRecord);
for(i=nRec-1; i>=0; i--){
rc = pager_playback_one_page(pPager, &pPager->jfd);
if( rc!=SQLITE_OK ) goto end_ckpt_playback;
}
end_ckpt_playback:
if( rc!=SQLITE_OK ){
pPager->errMask |= PAGER_ERR_CORRUPT;
rc = SQLITE_CORRUPT;
}
return rc;
}
/*
** Change the maximum number of in-memory pages that are allowed.
**
** The maximum number is the absolute value of the mxPage parameter.
** If mxPage is negative, the noSync flag is also set. noSync bypasses
** calls to sqliteOsSync(). The pager runs much faster with noSync on,
** but if the operating system crashes or there is an abrupt power
** failure, the database file might be left in an inconsistent and
** unrepairable state.
*/
void sqlitepager_set_cachesize(Pager *pPager, int mxPage){
if( mxPage>=0 ){
pPager->noSync = pPager->tempFile;
}else{
pPager->noSync = 1;
mxPage = -mxPage;
}
if( mxPage>10 ){
pPager->mxPage = mxPage;
}
}
/*
** Open a temporary file. Write the name of the file into zName
** (zName must be at least SQLITE_TEMPNAME_SIZE bytes long.) Write
** the file descriptor into *fd. Return SQLITE_OK on success or some
** other error code if we fail.
**
** The OS will automatically delete the temporary file when it is
** closed.
*/
static int sqlitepager_opentemp(char *zFile, OsFile *fd){
int cnt = 8;
int rc;
do{
cnt--;
sqliteOsTempFileName(zFile);
rc = sqliteOsOpenExclusive(zFile, fd, 1);
}while( cnt>0 && rc!=SQLITE_OK );
return rc;
}
/*
** Create a new page cache and put a pointer to the page cache in *ppPager.
** The file to be cached need not exist. The file is not locked until
** the first call to sqlitepager_get() and is only held open until the
** last page is released using sqlitepager_unref().
**
** If zFilename is NULL then a randomly-named temporary file is created
** and used as the file to be cached. The file will be deleted
** automatically when it is closed.
*/
int sqlitepager_open(
Pager **ppPager, /* Return the Pager structure here */
const char *zFilename, /* Name of the database file to open */
int mxPage, /* Max number of in-memory cache pages */
int nExtra /* Extra bytes append to each in-memory page */
){
Pager *pPager;
int nameLen;
OsFile fd;
int rc;
int tempFile;
int readOnly = 0;
char zTemp[SQLITE_TEMPNAME_SIZE];
*ppPager = 0;
if( sqlite_malloc_failed ){
return SQLITE_NOMEM;
}
if( zFilename ){
rc = sqliteOsOpenReadWrite(zFilename, &fd, &readOnly);
tempFile = 0;
}else{
rc = sqlitepager_opentemp(zTemp, &fd);
zFilename = zTemp;
tempFile = 1;
}
if( rc!=SQLITE_OK ){
return SQLITE_CANTOPEN;
}
nameLen = strlen(zFilename);
pPager = sqliteMalloc( sizeof(*pPager) + nameLen*2 + 30 );
if( pPager==0 ){
sqliteOsClose(&fd);
return SQLITE_NOMEM;
}
pPager->zFilename = (char*)&pPager[1];
pPager->zJournal = &pPager->zFilename[nameLen+1];
strcpy(pPager->zFilename, zFilename);
strcpy(pPager->zJournal, zFilename);
strcpy(&pPager->zJournal[nameLen], "-journal");
pPager->fd = fd;
pPager->journalOpen = 0;
pPager->ckptOpen = 0;
pPager->ckptInUse = 0;
pPager->nRef = 0;
pPager->dbSize = -1;
pPager->ckptSize = 0;
pPager->ckptJSize = 0;
pPager->nPage = 0;
pPager->mxPage = mxPage>5 ? mxPage : 10;
pPager->state = SQLITE_UNLOCK;
pPager->errMask = 0;
pPager->tempFile = tempFile;
pPager->readOnly = readOnly;
pPager->needSync = 0;
pPager->noSync = pPager->tempFile;
pPager->pFirst = 0;
pPager->pLast = 0;
pPager->nExtra = nExtra;
memset(pPager->aHash, 0, sizeof(pPager->aHash));
*ppPager = pPager;
return SQLITE_OK;
}
/*
** Set the destructor for this pager. If not NULL, the destructor is called
** when the reference count on each page reaches zero. The destructor can
** be used to clean up information in the extra segment appended to each page.
**
** The destructor is not called as a result sqlitepager_close().
** Destructors are only called by sqlitepager_unref().
*/
void sqlitepager_set_destructor(Pager *pPager, void (*xDesc)(void*)){
pPager->xDestructor = xDesc;
}
/*
** Return the total number of pages in the disk file associated with
** pPager.
*/
int sqlitepager_pagecount(Pager *pPager){
int n;
assert( pPager!=0 );
if( pPager->dbSize>=0 ){
return pPager->dbSize;
}
if( sqliteOsFileSize(&pPager->fd, &n)!=SQLITE_OK ){
pPager->errMask |= PAGER_ERR_DISK;
return 0;
}
n /= SQLITE_PAGE_SIZE;
if( pPager->state!=SQLITE_UNLOCK ){
pPager->dbSize = n;
}
return n;
}
/*
** Shutdown the page cache. Free all memory and close all files.
**
** If a transaction was in progress when this routine is called, that
** transaction is rolled back. All outstanding pages are invalidated
** and their memory is freed. Any attempt to use a page associated
** with this page cache after this function returns will likely
** result in a coredump.
*/
int sqlitepager_close(Pager *pPager){
PgHdr *pPg, *pNext;
switch( pPager->state ){
case SQLITE_WRITELOCK: {
sqlitepager_rollback(pPager);
sqliteOsUnlock(&pPager->fd);
assert( pPager->journalOpen==0 );
break;
}
case SQLITE_READLOCK: {
sqliteOsUnlock(&pPager->fd);
break;
}
default: {
/* Do nothing */
break;
}
}
for(pPg=pPager->pAll; pPg; pPg=pNext){
pNext = pPg->pNextAll;
sqliteFree(pPg);
}
sqliteOsClose(&pPager->fd);
assert( pPager->journalOpen==0 );
/* Temp files are automatically deleted by the OS
** if( pPager->tempFile ){
** sqliteOsDelete(pPager->zFilename);
** }
*/
sqliteFree(pPager);
return SQLITE_OK;
}
/*
** Return the page number for the given page data.
*/
Pgno sqlitepager_pagenumber(void *pData){
PgHdr *p = DATA_TO_PGHDR(pData);
return p->pgno;
}
/*
** Increment the reference count for a page. If the page is
** currently on the freelist (the reference count is zero) then
** remove it from the freelist.
*/
static void page_ref(PgHdr *pPg){
if( pPg->nRef==0 ){
/* The page is currently on the freelist. Remove it. */
if( pPg->pPrevFree ){
pPg->pPrevFree->pNextFree = pPg->pNextFree;
}else{
pPg->pPager->pFirst = pPg->pNextFree;
}
if( pPg->pNextFree ){
pPg->pNextFree->pPrevFree = pPg->pPrevFree;
}else{
pPg->pPager->pLast = pPg->pPrevFree;
}
pPg->pPager->nRef++;
}
pPg->nRef++;
REFINFO(pPg);
}
/*
** Increment the reference count for a page. The input pointer is
** a reference to the page data.
*/
int sqlitepager_ref(void *pData){
PgHdr *pPg = DATA_TO_PGHDR(pData);
page_ref(pPg);
return SQLITE_OK;
}
/*
** Sync the journal and then write all free dirty pages to the database
** file.
**
** Writing all free dirty pages to the database after the sync is a
** non-obvious optimization. fsync() is an expensive operation so we
** want to minimize the number ot times it is called. After an fsync() call,
** we are free to write dirty pages back to the database. It is best
** to go ahead and write as many dirty pages as possible to minimize
** the risk of having to do another fsync() later on. Writing dirty
** free pages in this way was observed to make database operations go
** up to 10 times faster.
**
** If we are writing to temporary database, there is no need to preserve
** the integrity of the journal file, so we can save time and skip the
** fsync().
*/
static int syncAllPages(Pager *pPager){
PgHdr *pPg;
int rc = SQLITE_OK;
if( pPager->needSync ){
if( !pPager->tempFile ){
rc = sqliteOsSync(&pPager->jfd);
if( rc!=0 ) return rc;
}
pPager->needSync = 0;
}
for(pPg=pPager->pFirst; pPg; pPg=pPg->pNextFree){
if( pPg->dirty ){
sqliteOsSeek(&pPager->fd, (pPg->pgno-1)*SQLITE_PAGE_SIZE);
rc = sqliteOsWrite(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ) break;
pPg->dirty = 0;
}
}
return rc;
}
/*
** Acquire a page.
**
** A read lock on the disk file is obtained when the first page is acquired.
** This read lock is dropped when the last page is released.
**
** A _get works for any page number greater than 0. If the database
** file is smaller than the requested page, then no actual disk
** read occurs and the memory image of the page is initialized to
** all zeros. The extra data appended to a page is always initialized
** to zeros the first time a page is loaded into memory.
**
** The acquisition might fail for several reasons. In all cases,
** an appropriate error code is returned and *ppPage is set to NULL.
**
** See also sqlitepager_lookup(). Both this routine and _lookup() attempt
** to find a page in the in-memory cache first. If the page is not already
** in memory, this routine goes to disk to read it in whereas _lookup()
** just returns 0. This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** or journal files.
*/
int sqlitepager_get(Pager *pPager, Pgno pgno, void **ppPage){
PgHdr *pPg;
/* Make sure we have not hit any critical errors.
*/
if( pPager==0 || pgno==0 ){
return SQLITE_ERROR;
}
if( pPager->errMask & ~(PAGER_ERR_FULL) ){
return pager_errcode(pPager);
}
/* If this is the first page accessed, then get a read lock
** on the database file.
*/
if( pPager->nRef==0 ){
if( sqliteOsReadLock(&pPager->fd)!=SQLITE_OK ){
*ppPage = 0;
return SQLITE_BUSY;
}
pPager->state = SQLITE_READLOCK;
/* If a journal file exists, try to play it back.
*/
if( sqliteOsFileExists(pPager->zJournal) ){
int rc, dummy;
/* Get a write lock on the database
*/
rc = sqliteOsWriteLock(&pPager->fd);
if( rc!=SQLITE_OK ){
rc = sqliteOsUnlock(&pPager->fd);
assert( rc==SQLITE_OK );
*ppPage = 0;
return SQLITE_BUSY;
}
pPager->state = SQLITE_WRITELOCK;
/* Open the journal for exclusive access. Return SQLITE_BUSY if
** we cannot get exclusive access to the journal file.
**
** Even though we will only be reading from the journal, not writing,
** we have to open the journal for writing in order to obtain an
** exclusive access lock.
*/
rc = sqliteOsOpenReadWrite(pPager->zJournal, &pPager->jfd, &dummy);
if( rc!=SQLITE_OK ){
rc = sqliteOsUnlock(&pPager->fd);
assert( rc==SQLITE_OK );
*ppPage = 0;
return SQLITE_BUSY;
}
pPager->journalOpen = 1;
/* Playback and delete the journal. Drop the database write
** lock and reacquire the read lock.
*/
rc = pager_playback(pPager);
if( rc!=SQLITE_OK ){
return rc;
}
}
pPg = 0;
}else{
/* Search for page in cache */
pPg = pager_lookup(pPager, pgno);
}
if( pPg==0 ){
/* The requested page is not in the page cache. */
int h;
pPager->nMiss++;
if( pPager->nPage<pPager->mxPage || pPager->pFirst==0 ){
/* Create a new page */
pPg = sqliteMalloc( sizeof(*pPg) + SQLITE_PAGE_SIZE + pPager->nExtra );
if( pPg==0 ){
*ppPage = 0;
pager_unwritelock(pPager);
pPager->errMask |= PAGER_ERR_MEM;
return SQLITE_NOMEM;
}
pPg->pPager = pPager;
pPg->pNextAll = pPager->pAll;
if( pPager->pAll ){
pPager->pAll->pPrevAll = pPg;
}
pPg->pPrevAll = 0;
pPager->pAll = pPg;
pPager->nPage++;
}else{
/* Recycle an older page. First locate the page to be recycled.
** Try to find one that is not dirty and is near the head of
** of the free list */
pPg = pPager->pFirst;
while( pPg && pPg->dirty ){
pPg = pPg->pNextFree;
}
/* If we could not find a page that has not been used recently
** and which is not dirty, then sync the journal and write all
** dirty free pages into the database file, thus making them
** clean pages and available for recycling.
**
** We have to sync the journal before writing a page to the main
** database. But syncing is a very slow operation. So after a
** sync, it is best to write everything we can back to the main
** database to minimize the risk of having to sync again in the
** near future. That is way we write all dirty pages after a
** sync.
*/
if( pPg==0 ){
int rc = syncAllPages(pPager);
if( rc!=0 ){
sqlitepager_rollback(pPager);
*ppPage = 0;
return SQLITE_IOERR;
}
pPg = pPager->pFirst;
}
assert( pPg->nRef==0 );
assert( pPg->dirty==0 );
/* Unlink the old page from the free list and the hash table
*/
if( pPg->pPrevFree ){
pPg->pPrevFree->pNextFree = pPg->pNextFree;
}else{
assert( pPager->pFirst==pPg );
pPager->pFirst = pPg->pNextFree;
}
if( pPg->pNextFree ){
pPg->pNextFree->pPrevFree = pPg->pPrevFree;
}else{
assert( pPager->pLast==pPg );
pPager->pLast = pPg->pPrevFree;
}
pPg->pNextFree = pPg->pPrevFree = 0;
if( pPg->pNextHash ){
pPg->pNextHash->pPrevHash = pPg->pPrevHash;
}
if( pPg->pPrevHash ){
pPg->pPrevHash->pNextHash = pPg->pNextHash;
}else{
h = pager_hash(pPg->pgno);
assert( pPager->aHash[h]==pPg );
pPager->aHash[h] = pPg->pNextHash;
}
pPg->pNextHash = pPg->pPrevHash = 0;
pPager->nOvfl++;
}
pPg->pgno = pgno;
if( pPager->aInJournal && (int)pgno<=pPager->origDbSize ){
pPg->inJournal = (pPager->aInJournal[pgno/8] & (1<<(pgno&7)))!=0;
}else{
pPg->inJournal = 0;
}
if( pPager->aInCkpt && (int)pgno<=pPager->ckptSize ){
pPg->inCkpt = (pPager->aInCkpt[pgno/8] & (1<<(pgno&7)))!=0;
}else{
pPg->inCkpt = 0;
}
pPg->dirty = 0;
pPg->nRef = 1;
REFINFO(pPg);
pPager->nRef++;
h = pager_hash(pgno);
pPg->pNextHash = pPager->aHash[h];
pPager->aHash[h] = pPg;
if( pPg->pNextHash ){
assert( pPg->pNextHash->pPrevHash==0 );
pPg->pNextHash->pPrevHash = pPg;
}
if( pPager->dbSize<0 ) sqlitepager_pagecount(pPager);
if( pPager->dbSize<(int)pgno ){
memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
}else{
int rc;
sqliteOsSeek(&pPager->fd, (pgno-1)*SQLITE_PAGE_SIZE);
rc = sqliteOsRead(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ){
return rc;
}
}
if( pPager->nExtra>0 ){
memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
}
}else{
/* The requested page is in the page cache. */
pPager->nHit++;
page_ref(pPg);
}
*ppPage = PGHDR_TO_DATA(pPg);
return SQLITE_OK;
}
/*
** Acquire a page if it is already in the in-memory cache. Do
** not read the page from disk. Return a pointer to the page,
** or 0 if the page is not in cache.
**
** See also sqlitepager_get(). The difference between this routine
** and sqlitepager_get() is that _get() will go to the disk and read
** in the page if the page is not already in cache. This routine
** returns NULL if the page is not in cache or if a disk I/O error
** has ever happened.
*/
void *sqlitepager_lookup(Pager *pPager, Pgno pgno){
PgHdr *pPg;
/* Make sure we have not hit any critical errors.
*/
if( pPager==0 || pgno==0 ){
return 0;
}
if( pPager->errMask & ~(PAGER_ERR_FULL) ){
return 0;
}
if( pPager->nRef==0 ){
return 0;
}
pPg = pager_lookup(pPager, pgno);
if( pPg==0 ) return 0;
page_ref(pPg);
return PGHDR_TO_DATA(pPg);
}
/*
** Release a page.
**
** If the number of references to the page drop to zero, then the
** page is added to the LRU list. When all references to all pages
** are released, a rollback occurs and the lock on the database is
** removed.
*/
int sqlitepager_unref(void *pData){
PgHdr *pPg;
/* Decrement the reference count for this page
*/
pPg = DATA_TO_PGHDR(pData);
assert( pPg->nRef>0 );
pPg->nRef--;
REFINFO(pPg);
/* When the number of references to a page reach 0, call the
** destructor and add the page to the freelist.
*/
if( pPg->nRef==0 ){
Pager *pPager;
pPager = pPg->pPager;
pPg->pNextFree = 0;
pPg->pPrevFree = pPager->pLast;
pPager->pLast = pPg;
if( pPg->pPrevFree ){
pPg->pPrevFree->pNextFree = pPg;
}else{
pPager->pFirst = pPg;
}
if( pPager->xDestructor ){
pPager->xDestructor(pData);
}
/* When all pages reach the freelist, drop the read lock from
** the database file.
*/
pPager->nRef--;
assert( pPager->nRef>=0 );
if( pPager->nRef==0 ){
pager_reset(pPager);
}
}
return SQLITE_OK;
}
/*
** Acquire a write-lock on the database. The lock is removed when
** the any of the following happen:
**
** * sqlitepager_commit() is called.
** * sqlitepager_rollback() is called.
** * sqlitepager_close() is called.
** * sqlitepager_unref() is called to on every outstanding page.
**
** The parameter to this routine is a pointer to any open page of the
** database file. Nothing changes about the page - it is used merely
** to acquire a pointer to the Pager structure and as proof that there
** is already a read-lock on the database.
**
** If the database is already write-locked, this routine is a no-op.
*/
int sqlitepager_begin(void *pData){
PgHdr *pPg = DATA_TO_PGHDR(pData);
Pager *pPager = pPg->pPager;
int rc = SQLITE_OK;
assert( pPg->nRef>0 );
assert( pPager->state!=SQLITE_UNLOCK );
if( pPager->state==SQLITE_READLOCK ){
assert( pPager->aInJournal==0 );
rc = sqliteOsWriteLock(&pPager->fd);
if( rc!=SQLITE_OK ){
return rc;
}
pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
if( pPager->aInJournal==0 ){
sqliteOsReadLock(&pPager->fd);
return SQLITE_NOMEM;
}
rc = sqliteOsOpenExclusive(pPager->zJournal, &pPager->jfd, 0);
if( rc!=SQLITE_OK ){
sqliteFree(pPager->aInJournal);
pPager->aInJournal = 0;
sqliteOsReadLock(&pPager->fd);
return SQLITE_CANTOPEN;
}
pPager->journalOpen = 1;
pPager->needSync = 0;
pPager->dirtyFile = 0;
pPager->state = SQLITE_WRITELOCK;
sqlitepager_pagecount(pPager);
pPager->origDbSize = pPager->dbSize;
rc = sqliteOsWrite(&pPager->jfd, aJournalMagic, sizeof(aJournalMagic));
if( rc==SQLITE_OK ){
rc = sqliteOsWrite(&pPager->jfd, &pPager->dbSize, sizeof(Pgno));
}
if( rc!=SQLITE_OK ){
rc = pager_unwritelock(pPager);
if( rc==SQLITE_OK ) rc = SQLITE_FULL;
}
}
return rc;
}
/*
** Mark a data page as writeable. The page is written into the journal
** if it is not there already. This routine must be called before making
** changes to a page.
**
** The first time this routine is called, the pager creates a new
** journal and acquires a write lock on the database. If the write
** lock could not be acquired, this routine returns SQLITE_BUSY. The
** calling routine must check for that return value and be careful not to
** change any page data until this routine returns SQLITE_OK.
**
** If the journal file could not be written because the disk is full,
** then this routine returns SQLITE_FULL and does an immediate rollback.
** All subsequent write attempts also return SQLITE_FULL until there
** is a call to sqlitepager_commit() or sqlitepager_rollback() to
** reset.
*/
int sqlitepager_write(void *pData){
PgHdr *pPg = DATA_TO_PGHDR(pData);
Pager *pPager = pPg->pPager;
int rc = SQLITE_OK;
/* Check for errors
*/
if( pPager->errMask ){
return pager_errcode(pPager);
}
if( pPager->readOnly ){
return SQLITE_PERM;
}
/* Mark the page as dirty. If the page has already been written
** to the journal then we can return right away.
*/
pPg->dirty = 1;
if( pPg->inJournal && (pPg->inCkpt || pPager->ckptInUse==0) ){
pPager->dirtyFile = 1;
return SQLITE_OK;
}
/* If we get this far, it means that the page needs to be
** written to the transaction journal or the ckeckpoint journal
** or both.
**
** First check to see that the transaction journal exists and
** create it if it does not.
*/
assert( pPager->state!=SQLITE_UNLOCK );
rc = sqlitepager_begin(pData);
pPager->dirtyFile = 1;
if( rc!=SQLITE_OK ) return rc;
assert( pPager->state==SQLITE_WRITELOCK );
assert( pPager->journalOpen );
/* The transaction journal now exists and we have a write lock on the
** main database file. Write the current page to the transaction
** journal if it is not there already.
*/
if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
rc = sqliteOsWrite(&pPager->jfd, &pPg->pgno, sizeof(Pgno));
if( rc==SQLITE_OK ){
rc = sqliteOsWrite(&pPager->jfd, pData, SQLITE_PAGE_SIZE);
}
if( rc!=SQLITE_OK ){
sqlitepager_rollback(pPager);
pPager->errMask |= PAGER_ERR_FULL;
return rc;
}
assert( pPager->aInJournal!=0 );
pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPager->needSync = !pPager->noSync;
pPg->inJournal = 1;
if( pPager->ckptInUse ){
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
}
}
/* If the checkpoint journal is open and the page is not in it,
** then write the current page to the checkpoint journal.
*/
if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
rc = sqliteOsWrite(&pPager->cpfd, &pPg->pgno, sizeof(Pgno));
if( rc==SQLITE_OK ){
rc = sqliteOsWrite(&pPager->cpfd, pData, SQLITE_PAGE_SIZE);
}
if( rc!=SQLITE_OK ){
sqlitepager_rollback(pPager);
pPager->errMask |= PAGER_ERR_FULL;
return rc;
}
assert( pPager->aInCkpt!=0 );
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
}
/* Update the database size and return.
*/
if( pPager->dbSize<(int)pPg->pgno ){
pPager->dbSize = pPg->pgno;
}
return rc;
}
/*
** Return TRUE if the page given in the argument was previously passed
** to sqlitepager_write(). In other words, return TRUE if it is ok
** to change the content of the page.
*/
int sqlitepager_iswriteable(void *pData){
PgHdr *pPg = DATA_TO_PGHDR(pData);
return pPg->dirty;
}
/*
** A call to this routine tells the pager that it is not necessary to
** write the information on page "pgno" back to the disk, even though
** that page might be marked as dirty.
**
** The overlying software layer calls this routine when all of the data
** on the given page is unused. The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization, together with the
** sqlitepager_dont_rollback() below, more than double the speed
** of large INSERT operations and quadruple the speed of large DELETEs.
*/
void sqlitepager_dont_write(Pager *pPager, Pgno pgno){
PgHdr *pPg;
pPg = pager_lookup(pPager, pgno);
if( pPg && pPg->dirty ){
if( pPager->dbSize==(int)pPg->pgno && pPager->origDbSize<pPager->dbSize ){
/* If this pages is the last page in the file and the file has grown
** during the current transaction, then do NOT mark the page as clean.
** When the database file grows, we must make sure that the last page
** gets written at least once so that the disk file will be the correct
** size. If you do not write this page and the size of the file
** on the disk ends up being too small, that can lead to database
** corruption during the next transaction.
*/
}else{
pPg->dirty = 0;
}
}
}
/*
** A call to this routine tells the pager that if a rollback occurs,
** it is not necessary to restore the data on the given page. This
** means that the pager does not have to record the given page in the
** rollback journal.
*/
void sqlitepager_dont_rollback(void *pData){
PgHdr *pPg = DATA_TO_PGHDR(pData);
Pager *pPager = pPg->pPager;
if( pPager->state!=SQLITE_WRITELOCK || pPager->journalOpen==0 ) return;
if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
assert( pPager->aInJournal!=0 );
pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inJournal = 1;
if( pPager->ckptInUse ){
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
}
}
if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
assert( pPager->aInCkpt!=0 );
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
}
}
/*
** Commit all changes to the database and release the write lock.
**
** If the commit fails for any reason, a rollback attempt is made
** and an error code is returned. If the commit worked, SQLITE_OK
** is returned.
*/
int sqlitepager_commit(Pager *pPager){
int rc;
PgHdr *pPg;
if( pPager->errMask==PAGER_ERR_FULL ){
rc = sqlitepager_rollback(pPager);
if( rc==SQLITE_OK ) rc = SQLITE_FULL;
return rc;
}
if( pPager->errMask!=0 ){
rc = pager_errcode(pPager);
return rc;
}
if( pPager->state!=SQLITE_WRITELOCK ){
return SQLITE_ERROR;
}
assert( pPager->journalOpen );
if( pPager->dirtyFile==0 ){
/* Exit early (without doing the time-consuming sqliteOsSync() calls)
** if there have been no changes to the database file. */
rc = pager_unwritelock(pPager);
pPager->dbSize = -1;
return rc;
}
if( pPager->needSync && sqliteOsSync(&pPager->jfd)!=SQLITE_OK ){
goto commit_abort;
}
for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
if( pPg->dirty==0 ) continue;
rc = sqliteOsSeek(&pPager->fd, (pPg->pgno-1)*SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ) goto commit_abort;
rc = sqliteOsWrite(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ) goto commit_abort;
}
if( !pPager->noSync && sqliteOsSync(&pPager->fd)!=SQLITE_OK ){
goto commit_abort;
}
rc = pager_unwritelock(pPager);
pPager->dbSize = -1;
return rc;
/* Jump here if anything goes wrong during the commit process.
*/
commit_abort:
rc = sqlitepager_rollback(pPager);
if( rc==SQLITE_OK ){
rc = SQLITE_FULL;
}
return rc;
}
/*
** Rollback all changes. The database falls back to read-only mode.
** All in-memory cache pages revert to their original data contents.
** The journal is deleted.
**
** This routine cannot fail unless some other process is not following
** the correct locking protocol (SQLITE_PROTOCOL) or unless some other
** process is writing trash into the journal file (SQLITE_CORRUPT) or
** unless a prior malloc() failed (SQLITE_NOMEM). Appropriate error
** codes are returned for all these occasions. Otherwise,
** SQLITE_OK is returned.
*/
int sqlitepager_rollback(Pager *pPager){
int rc;
if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
if( pPager->state>=SQLITE_WRITELOCK ){
pager_playback(pPager);
}
return pager_errcode(pPager);
}
if( pPager->state!=SQLITE_WRITELOCK ){
return SQLITE_OK;
}
rc = pager_playback(pPager);
if( rc!=SQLITE_OK ){
rc = SQLITE_CORRUPT;
pPager->errMask |= PAGER_ERR_CORRUPT;
}
pPager->dbSize = -1;
return rc;
}
/*
** Return TRUE if the database file is opened read-only. Return FALSE
** if the database is (in theory) writable.
*/
int sqlitepager_isreadonly(Pager *pPager){
return pPager->readOnly;
}
/*
** This routine is used for testing and analysis only.
*/
int *sqlitepager_stats(Pager *pPager){
static int a[9];
a[0] = pPager->nRef;
a[1] = pPager->nPage;
a[2] = pPager->mxPage;
a[3] = pPager->dbSize;
a[4] = pPager->state;
a[5] = pPager->errMask;
a[6] = pPager->nHit;
a[7] = pPager->nMiss;
a[8] = pPager->nOvfl;
return a;
}
/*
** Set the checkpoint.
**
** This routine should be called with the transaction journal already
** open. A new checkpoint journal is created that can be used to rollback
** changes of a single SQL command within a larger transaction.
*/
int sqlitepager_ckpt_begin(Pager *pPager){
int rc;
char zTemp[SQLITE_TEMPNAME_SIZE];
assert( pPager->journalOpen );
assert( !pPager->ckptInUse );
pPager->aInCkpt = sqliteMalloc( pPager->dbSize/8 + 1 );
if( pPager->aInCkpt==0 ){
sqliteOsReadLock(&pPager->fd);
return SQLITE_NOMEM;
}
rc = sqliteOsFileSize(&pPager->jfd, &pPager->ckptJSize);
if( rc ) goto ckpt_begin_failed;
pPager->ckptSize = pPager->dbSize;
if( !pPager->ckptOpen ){
rc = sqlitepager_opentemp(zTemp, &pPager->cpfd);
if( rc ) goto ckpt_begin_failed;
pPager->ckptOpen = 1;
}
pPager->ckptInUse = 1;
return SQLITE_OK;
ckpt_begin_failed:
if( pPager->aInCkpt ){
sqliteFree(pPager->aInCkpt);
pPager->aInCkpt = 0;
}
return rc;
}
/*
** Commit a checkpoint.
*/
int sqlitepager_ckpt_commit(Pager *pPager){
if( pPager->ckptInUse ){
PgHdr *pPg;
sqliteOsTruncate(&pPager->cpfd, 0);
pPager->ckptInUse = 0;
sqliteFree( pPager->aInCkpt );
pPager->aInCkpt = 0;
for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
pPg->inCkpt = 0;
}
}
return SQLITE_OK;
}
/*
** Rollback a checkpoint.
*/
int sqlitepager_ckpt_rollback(Pager *pPager){
int rc;
if( pPager->ckptInUse ){
rc = pager_ckpt_playback(pPager);
sqlitepager_ckpt_commit(pPager);
}else{
rc = SQLITE_OK;
}
return rc;
}
#if SQLITE_TEST
/*
** Print a listing of all referenced pages and their ref count.
*/
void sqlitepager_refdump(Pager *pPager){
PgHdr *pPg;
for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
if( pPg->nRef<=0 ) continue;
printf("PAGE %3d addr=0x%08x nRef=%d\n",
pPg->pgno, (int)PGHDR_TO_DATA(pPg), pPg->nRef);
}
}
#endif