SQLite

**
** Setting the size limit to -1 means no limit is enforced.
** An attempt to set a limit smaller than -1 is a no-op.
*/
i64 sqlite3PagerJournalSizeLimit(Pager *pPager, i64 iLimit){
  if( iLimit>=-1 ){
    pPager->journalSizeLimit = iLimit;
    sqlite3WalLimit(pPager->pWal, iLimit);
  }
  return pPager->journalSizeLimit;
}

/*
** Return a pointer to the pPager->pBackup variable. The backup module
** in backup.c maintains the content of this variable. This module

  }

  /* Open the connection to the log file. If this operation fails, 
  ** (e.g. due to malloc() failure), return an error code.
  */
  if( rc==SQLITE_OK ){
    rc = sqlite3WalOpen(pPager->pVfs, 
        pPager->fd, pPager->zWal, pPager->exclusiveMode,
        pPager->journalSizeLimit, &pPager->pWal
    );
  }

  return rc;
}

** 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 */
  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 */

** 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] );

    return SQLITE_NOMEM;
  }

  pRet->pVfs = pVfs;
  pRet->pWalFd = (sqlite3_file *)&pRet[1];
  pRet->pDbFd = pDbFd;
  pRet->readLock = -1;
  pRet->mxWalSize = mxWalSize;
  pRet->zWalName = zWalName;
  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 = 1;
  }

  if( rc!=SQLITE_OK ){
    walIndexClose(pRet, 0);
    sqlite3OsClose(pRet->pWalFd);
    sqlite3_free(pRet);
  }else{
    *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.

        ** 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.
        */
        int i;                    /* Loop counter */
        u32 *aSalt = pWal->hdr.aSalt;       /* Big-endian salt values */

        /* Limit the size of WAL file if the journal_size_limit PRAGMA is
        ** set to a non-negative value.  Log errors encountered
        ** during the truncation attempt. */
        if( pWal->mxWalSize>=0 ){
          i64 sz;
          int rx;
          rx = sqlite3OsFileSize(pWal->pWalFd, &sz);
          if( rx==SQLITE_OK && (sz > pWal->mxWalSize) ){
            rx = sqlite3OsTruncate(pWal->pWalFd, pWal->mxWalSize);
          }
          if( rx ){
            sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName);
          }
        }

        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;

#ifndef _WAL_H_
#define _WAL_H_

#include "sqliteInt.h"

#ifdef SQLITE_OMIT_WAL
# define sqlite3WalOpen(x,y,z)                   0
# define sqlite3WalLimit(x,y)
# define sqlite3WalClose(w,x,y,z)                0
# define sqlite3WalBeginReadTransaction(y,z)     0
# define sqlite3WalEndReadTransaction(z)
# define sqlite3WalRead(v,w,x,y,z)               0
# define sqlite3WalDbsize(y)                     0
# define sqlite3WalBeginWriteTransaction(y)      0
# define sqlite3WalEndWriteTransaction(x)        0

/* Connection to a write-ahead log (WAL) file. 
** There is one object of this type for each pager. 
*/
typedef struct Wal Wal;

/* Open and close a connection to a write-ahead log. */
int sqlite3WalOpen(sqlite3_vfs*, sqlite3_file*, const char *, int, i64, Wal**);
int sqlite3WalClose(Wal *pWal, int sync_flags, int, u8 *);

/* Set the limiting size of a WAL file. */
void sqlite3WalLimit(Wal*, i64);

/* Used by readers to open (lock) and close (unlock) a snapshot.  A 
** snapshot is like a read-transaction.  It is the state of the database
** at an instant in time.  sqlite3WalOpenSnapshot gets a read lock and
** preserves the current state even if the other threads or processes
** write to or checkpoint the WAL.  sqlite3WalCloseSnapshot() closes the
** transaction and releases the lock.

# 2011 May 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 file implements regression tests for SQLite library.  The
# focus of this file is testing the PRAGMA journal_size_limit when
# in WAL mode.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
ifcapable !wal {finish_test ; return }

# Case 1:  No size limit.  Journal can get large.
#
do_test wal7-1.0 {
  db close
  forcedelete test.db
  sqlite3 db test.db
  db eval {
    PRAGMA page_size=1024;
    PRAGMA journal_mode=WAL;
    PRAGMA wal_autocheckpoint=50;  -- 50 pages
    CREATE TABLE t1(x, y UNIQUE);
    INSERT INTO t1 VALUES(1,2);
    INSERT INTO t1 VALUES(zeroblob(200000),4);
    CREATE TABLE t2(z);
    DELETE FROM t1;
    INSERT INTO t2 SELECT x FROM t1;
  }
  expr {[file size test.db-wal]>50*1100}
} 1
do_test wal7-1.1 {
  db eval {PRAGMA wal_checkpoint}
  expr {[file size test.db-wal]>50*1100}
} 1
do_test wal7-1.2 {
  db eval {INSERT INTO t2 VALUES('hi');}
  expr {[file size test.db-wal]>50*1100}
} 1

# Case 2:  Size limit at half the autocheckpoint size.
#
do_test wal7-2.0 {
  db close
  forcedelete test.db
  sqlite3 db test.db
  db eval {
    PRAGMA page_size=1024;
    PRAGMA journal_mode=WAL;
    PRAGMA wal_autocheckpoint=50;  -- 50 pages
    PRAGMA journal_size_limit=25000;
    CREATE TABLE t1(x, y UNIQUE);
    INSERT INTO t1 VALUES(1,2);
    INSERT INTO t1 VALUES(zeroblob(200000),4);
    CREATE TABLE t2(z);
    DELETE FROM t1;
    INSERT INTO t2 SELECT x FROM t1;
  }
  file size test.db-wal
} 25000


# Case 3:  Size limit of zero.
#
do_test wal7-3.0 {
  db close
  forcedelete test.db
  sqlite3 db test.db
  db eval {
    PRAGMA page_size=1024;
    PRAGMA journal_mode=WAL;
    PRAGMA wal_autocheckpoint=50;  -- 50 pages
    PRAGMA journal_size_limit=0;
    CREATE TABLE t1(x, y UNIQUE);
    INSERT INTO t1 VALUES(1,2);
    INSERT INTO t1 VALUES(zeroblob(200000),4);
    CREATE TABLE t2(z);
    DELETE FROM t1;
    INSERT INTO t2 SELECT x FROM t1;
  }
  set sz [file size test.db-wal]
  expr {$sz>0 && $sz<10000}
} 1


# Case 4:  Size limit set before going WAL
#
do_test wal7-4.0 {
  db close
  forcedelete test.db
  sqlite3 db test.db
  db eval {
    PRAGMA page_size=1024;
    PRAGMA journal_size_limit=25000;
    PRAGMA journal_mode=WAL;
    PRAGMA wal_autocheckpoint=50;  -- 50 pages
    CREATE TABLE t1(x, y UNIQUE);
    INSERT INTO t1 VALUES(1,2);
    INSERT INTO t1 VALUES(zeroblob(200000),4);
    CREATE TABLE t2(z);
    DELETE FROM t1;
    INSERT INTO t2 SELECT x FROM t1;
  }
  set sz [file size test.db-wal]
} 25000





finish_test