SQLite

  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 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 */
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  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
};

 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(

      }
      rc = sqlite3WalCheckpoint(
          pWal, SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
      );
      sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersistWal);
      if( rc==SQLITE_OK && bPersistWal!=1 ){
        isDelete = 1;
      }else if( pWal->mxWalSize>=0 ){
        walLimitSize(pWal, pWal->mxWalSize);
      }
    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){
      sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);

** 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->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.

        ** 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.
        */
        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]));
        aSalt[1] = salt1;
        walIndexWriteHdr(pWal);
        pInfo->nBackfill = 0;
        for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;

    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;
    }
  }

      }
      nLast++;
      iOffset += szPage;
    }

    rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
  }

  if( isCommit && pWal->truncateOnCommit && pWal->mxWalSize>=0 ){
    i64 sz = pWal->mxWalSize;
    if( walFrameOffset(iFrame+nLast+1, szPage)>pWal->mxWalSize ){
      sz = walFrameOffset(iFrame+nLast+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;

# 2011 December 16
#
# 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 test simulates an application crash immediately following a
# system call to truncate a file. Specifically, the system call that
# truncates the WAL file if "PRAGMA journal_size_limit" is configured.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

ifcapable !wal {finish_test ; return }
set testprefix walcrash3

db close
testvfs tvfs
tvfs filter {xTruncate xWrite}
tvfs script tvfs_callback
proc tvfs_callback {args} {}

sqlite3 db test.db -vfs tvfs
do_execsql_test 1.1 {
  PRAGMA page_size = 1024;
  PRAGMA journal_mode = WAL;
  PRAGMA wal_autocheckpoint = 128;
  PRAGMA journal_size_limit = 16384;

  CREATE TABLE t1(a BLOB, b BLOB, UNIQUE(a, b));
  INSERT INTO t1 VALUES(randomblob(10), randomblob(1000));
} {wal 128 16384}

proc tvfs_callback {method file arglist} {
  if {$::state==1} {
    foreach f [glob -nocomplain xx_test.*] { forcedelete $f }
    foreach f [glob -nocomplain test.*]    { forcecopy $f "xx_$f" }
    set ::state 2
  }
  if {$::state==0 && $method=="xTruncate" && [file tail $file]=="test.db-wal"} {
    set ::state 1
  }
}

for {set i 2} {$i<1000} {incr i} {

  # If the WAL file is truncated within the following, within the following
  # xWrite call the [tvfs_callback] makes a copy of the database and WAL 
  # files set sets $::state to 2. So that the copied files are in the same
  # state as the real database and WAL files would be if an application crash 
  # occurred immediately following the xTruncate().
  # 
  set ::state 0
  do_execsql_test 1.$i.1 {
    INSERT INTO t1 VALUES(randomblob(10), randomblob(1000));
  }

  # If a copy was made, open it and run the integrity-check.
  #
  if {$::state==2} {
    sqlite3 db2 xx_test.db
    do_test 1.$i.2 { execsql { PRAGMA integrity_check  } db2 } "ok"
    do_test 1.$i.3 { execsql { SELECT count(*) FROM t1 } db2 } [expr $i-1]
    db2 close
  }
}

finish_test