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Overview
Comment:Add untested implementations of experimental APIs sqlite3_snapshot_get(), _open() and _free().
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Timelines: family | ancestors | descendants | both | snapshot-get
Files: files | file ages | folders
SHA1: 0715eb00aa8891400cd50a15509d3d7b13789626
User & Date: dan 2015-12-05 20:51:54
Context
2015-12-07
14:33
Add tests for snapshot_get(), _open() and _free(). check-in: 502cc6f3 user: dan tags: snapshot-get
2015-12-05
20:51
Add untested implementations of experimental APIs sqlite3_snapshot_get(), _open() and _free(). check-in: 0715eb00 user: dan tags: snapshot-get
2015-12-04
13:44
Remove the dependence on "exec ls -U" from the vtabH.test module, as the -U option to "ls" is not universally available. check-in: 4ecbc75b user: drh tags: trunk
Changes
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Changes to src/main.c.

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    (void)SQLITE_MISUSE_BKPT;
    return -1;
  }
#endif
  pBt = sqlite3DbNameToBtree(db, zDbName);
  return pBt ? sqlite3BtreeIsReadonly(pBt) : -1;
}

























































































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    (void)SQLITE_MISUSE_BKPT;
    return -1;
  }
#endif
  pBt = sqlite3DbNameToBtree(db, zDbName);
  return pBt ? sqlite3BtreeIsReadonly(pBt) : -1;
}

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Obtain a snapshot handle for the snapshot of database zDb currently 
** being read by handle db.
*/
int sqlite3_snapshot_get(
  sqlite3 *db, 
  const char *zDb,
  sqlite3_snapshot **ppSnapshot
){
  int rc = SQLITE_ERROR;
#ifndef SQLITE_OMIT_WAL
  int iDb;

#ifdef SQLITE_ENABLE_API_ARMOR
  if( !sqlite3SafetyCheckOk(db) ){
    return SQLITE_MISUSE_BKPT;
  }
#endif
  sqlite3_mutex_enter(db->mutex);

  iDb = sqlite3FindDbName(db, zDb);
  if( iDb==0 || iDb>1 ){
    Btree *pBt = db->aDb[iDb].pBt;
    if( 0!=sqlite3BtreeIsInReadTrans(pBt) 
     && 0==sqlite3BtreeIsInTrans(pBt)
    ){
      rc = sqlite3PagerSnapshotGet(sqlite3BtreePager(pBt), ppSnapshot);
    }
  }

  sqlite3_mutex_leave(db->mutex);
#endif   /* SQLITE_OMIT_WAL */
  return rc;
}

/*
** Open a read-transaction on the snapshot idendified by pSnapshot.
*/
int sqlite3_snapshot_open(
  sqlite3 *db, 
  const char *zDb, 
  sqlite3_snapshot *pSnapshot
){
  int rc = SQLITE_ERROR;
#ifndef SQLITE_OMIT_WAL

#ifdef SQLITE_ENABLE_API_ARMOR
  if( !sqlite3SafetyCheckOk(db) ){
    return SQLITE_MISUSE_BKPT;
  }
#endif
  sqlite3_mutex_enter(db->mutex);
  if( db->autoCommit==0 ){
    int iDb;
    iDb = sqlite3FindDbName(db, zDb);
    if( iDb==0 || iDb>1 ){
      Btree *pBt = db->aDb[iDb].pBt;
      if( 0==sqlite3BtreeIsInReadTrans(pBt) ){
        rc = sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), pSnapshot);
        if( rc==SQLITE_OK ){
          rc = sqlite3BtreeBeginTrans(pBt, 0);
          sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), 0);
        }
      }
    }
  }

  sqlite3_mutex_leave(db->mutex);
#endif   /* SQLITE_OMIT_WAL */
  return rc;
}

/*
** Free a snapshot handle obtained from sqlite3_snapshot_get().
*/
void sqlite3_snapshot_free(sqlite3_snapshot *pSnapshot){
  sqlite3_free(pSnapshot);
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

Changes to src/pager.c.

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      pPager->pWal = 0;
      pagerFixMaplimit(pPager);
    }
  }
  return rc;
}





























#endif /* !SQLITE_OMIT_WAL */

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** A read-lock must be held on the pager when this function is called. If
** the pager is in WAL mode and the WAL file currently contains one or more
** frames, return the size in bytes of the page images stored within the







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      pPager->pWal = 0;
      pagerFixMaplimit(pPager);
    }
  }
  return rc;
}

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** If this is a WAL database, obtain a snapshot handle for the snapshot
** currently open. Otherwise, return an error.
*/
int sqlite3PagerSnapshotGet(Pager *pPager, sqlite3_snapshot **ppSnapshot){
  int rc = SQLITE_ERROR;
  if( pPager->pWal ){
    rc = sqlite3WalSnapshotGet(pPager->pWal, ppSnapshot);
  }
  return rc;
}

/*
** If this is a WAL database, store a pointer to pSnapshot. Next time a
** read transaction is opened, attempt to read from the snapshot it 
** identifies. If this is not a WAL database, return an error.
*/
int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot){
  int rc = SQLITE_OK;
  if( pPager->pWal ){
    sqlite3WalSnapshotOpen(pPager->pWal, pSnapshot);
  }else{
    rc = SQLITE_ERROR;
  }
  return rc;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */
#endif /* !SQLITE_OMIT_WAL */

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** A read-lock must be held on the pager when this function is called. If
** the pager is in WAL mode and the WAL file currently contains one or more
** frames, return the size in bytes of the page images stored within the

Changes to src/pager.h.

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#ifndef SQLITE_OMIT_WAL
  int sqlite3PagerCheckpoint(Pager *pPager, int, int*, int*);
  int sqlite3PagerWalSupported(Pager *pPager);
  int sqlite3PagerWalCallback(Pager *pPager);
  int sqlite3PagerOpenWal(Pager *pPager, int *pisOpen);
  int sqlite3PagerCloseWal(Pager *pPager);




#endif

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */







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#ifndef SQLITE_OMIT_WAL
  int sqlite3PagerCheckpoint(Pager *pPager, int, int*, int*);
  int sqlite3PagerWalSupported(Pager *pPager);
  int sqlite3PagerWalCallback(Pager *pPager);
  int sqlite3PagerOpenWal(Pager *pPager, int *pisOpen);
  int sqlite3PagerCloseWal(Pager *pPager);
# ifdef SQLITE_ENABLE_SNAPSHOT
  int sqlite3PagerSnapshotGet(Pager *pPager, sqlite3_snapshot **ppSnapshot);
  int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot);
# endif
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */

Changes to src/sqlite.h.in.

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** Otherwise, if no error occurs, SQLITE_OK is returned.
**
** This function does not set the database handle error code or message
** returned by the sqlite3_errcode() and sqlite3_errmsg() functions.
*/
int sqlite3_db_cacheflush(sqlite3*);
























/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif /* _SQLITE3_H_ */







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** Otherwise, if no error occurs, SQLITE_OK is returned.
**
** This function does not set the database handle error code or message
** returned by the sqlite3_errcode() and sqlite3_errmsg() functions.
*/
int sqlite3_db_cacheflush(sqlite3*);

/*
** CAPI3REF: Open old database snapshots.
**
** The second argument passed to sqlite3_snapshot_get() must be the name
** of a database file attached to the database handle passed as the first.
** The database handle must have an open read transaction on the named 
** database, which must be in wal mode. 
**
** If successful, sqlite3_snapshot_get() sets *ppSnapshot to point to a new
** snapshot handle that may be used with sqlite3_snapshot_open() and returns
** SQLITE_OK.
**
** If the specified database does not exist, or is not a wal mode database, 
** or the database handle does not have an open read transaction on it,
** SQLITE_ERROR is returned. If any other error occurs, for example an IO 
** error or an OOM condition, the corresponding SQLite error code is 
** returned.
*/
typedef struct sqlite3_snapshot sqlite3_snapshot;
int sqlite3_snapshot_get(sqlite3*, const char*, sqlite3_snapshot **ppSnapshot);
int sqlite3_snapshot_open(sqlite3*, const char*, sqlite3_snapshot*);
void sqlite3_snapshot_free(sqlite3_snapshot*);

/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif /* _SQLITE3_H_ */

Changes to src/test1.c.

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    Tcl_WrongNumArgs(interp, 1, objv, "");
    return TCL_ERROR;
  }
  pVfs->xCurrentTimeInt64(pVfs, &t);
  Tcl_SetObjResult(interp, Tcl_NewWideIntObj(t));
  return TCL_OK;
}



















































































/*
** Usage:  sqlite3_next_stmt  DB  STMT
**
** Return the next statment in sequence after STMT.
*/
static int test_next_stmt(
................................................................................
     { "sqlite3_stmt_scanstatus",       test_stmt_scanstatus,   0 },
     { "sqlite3_stmt_scanstatus_reset", test_stmt_scanstatus_reset,   0 },
#endif
#ifdef SQLITE_ENABLE_SQLLOG
     { "sqlite3_config_sqllog",         test_config_sqllog,   0 },
#endif
     { "vfs_current_time_int64",           vfsCurrentTimeInt64,   0 },





  };
  static int bitmask_size = sizeof(Bitmask)*8;
  static int longdouble_size = sizeof(LONGDOUBLE_TYPE);
  int i;
  extern int sqlite3_sync_count, sqlite3_fullsync_count;
  extern int sqlite3_opentemp_count;
  extern int sqlite3_like_count;







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    Tcl_WrongNumArgs(interp, 1, objv, "");
    return TCL_ERROR;
  }
  pVfs->xCurrentTimeInt64(pVfs, &t);
  Tcl_SetObjResult(interp, Tcl_NewWideIntObj(t));
  return TCL_OK;
}

/*
** Usage: sqlite3_snapshot_get DB DBNAME
*/
static int test_snapshot_get(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;
  sqlite3 *db;
  char *zName;
  sqlite3_snapshot *pSnapshot = 0;

  if( objc!=3 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
  zName = Tcl_GetString(objv[2]);

  rc = sqlite3_snapshot_get(db, zName, &pSnapshot);
  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }else{
    char zBuf[100];
    if( sqlite3TestMakePointerStr(interp, zBuf, pSnapshot) ) return TCL_ERROR;
    Tcl_SetObjResult(interp, Tcl_NewStringObj(zBuf, -1));
  }
  return TCL_OK;
}

/*
** Usage: sqlite3_snapshot_open DB DBNAME SNAPSHOT
*/
static int test_snapshot_open(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;
  sqlite3 *db;
  char *zName;
  sqlite3_snapshot *pSnapshot;

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME SNAPSHOT");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
  zName = Tcl_GetString(objv[2]);
  pSnapshot = (sqlite3_snapshot*)sqlite3TestTextToPtr(Tcl_GetString(objv[3]));

  rc = sqlite3_snapshot_open(db, zName, pSnapshot);
  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** Usage: sqlite3_snapshot_free SNAPSHOT
*/
static int test_snapshot_free(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  sqlite3_snapshot *pSnapshot;
  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "SNAPSHOT");
    return TCL_ERROR;
  }
  pSnapshot = (sqlite3_snapshot*)sqlite3TestTextToPtr(Tcl_GetString(objv[1]));
  sqlite3_snapshot_free(pSnapshot);
  return TCL_OK;
}

/*
** Usage:  sqlite3_next_stmt  DB  STMT
**
** Return the next statment in sequence after STMT.
*/
static int test_next_stmt(
................................................................................
     { "sqlite3_stmt_scanstatus",       test_stmt_scanstatus,   0 },
     { "sqlite3_stmt_scanstatus_reset", test_stmt_scanstatus_reset,   0 },
#endif
#ifdef SQLITE_ENABLE_SQLLOG
     { "sqlite3_config_sqllog",         test_config_sqllog,   0 },
#endif
     { "vfs_current_time_int64",           vfsCurrentTimeInt64,   0 },
#ifdef SQLITE_ENABLE_SNAPSHOT
     { "sqlite3_snapshot_get", test_snapshot_get, 0 },
     { "sqlite3_snapshot_open", test_snapshot_open, 0 },
     { "sqlite3_snapshot_free", test_snapshot_free, 0 },
#endif
  };
  static int bitmask_size = sizeof(Bitmask)*8;
  static int longdouble_size = sizeof(LONGDOUBLE_TYPE);
  int i;
  extern int sqlite3_sync_count, sqlite3_fullsync_count;
  extern int sqlite3_opentemp_count;
  extern int sqlite3_like_count;

Changes to src/wal.c.

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  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  u32 minFrame;              /* Ignore wal frames before this one */
  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



};

/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE     0
#define WAL_EXCLUSIVE_MODE  1     
................................................................................
*/
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  */


  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
................................................................................
    }
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }

  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){





    /* 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)) ){
................................................................................
  /* 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;




  for(i=1; i<WAL_NREADER; i++){
    u32 thisMark = pInfo->aReadMark[i];
    if( mxReadMark<=thisMark && thisMark<=pWal->hdr.mxFrame ){
      assert( thisMark!=READMARK_NOT_USED );
      mxReadMark = thisMark;
      mxI = i;
    }
  }
  /* There was once an "if" here. The extra "{" is to preserve indentation. */
  {
    if( (pWal->readOnly & WAL_SHM_RDONLY)==0
     && (mxReadMark<pWal->hdr.mxFrame || mxI==0)
    ){
      for(i=1; i<WAL_NREADER; i++){
        rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
        if( rc==SQLITE_OK ){
          mxReadMark = pInfo->aReadMark[i] = pWal->hdr.mxFrame;
          mxI = i;
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
          break;
        }else if( rc!=SQLITE_BUSY ){
          return rc;
        }
      }
................................................................................
** 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 */









  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 );


























  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
................................................................................
** 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_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

#endif /* #ifndef SQLITE_OMIT_WAL */







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  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  u32 minFrame;              /* Ignore wal frames before this one */
  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;
#endif
};

/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE     0
#define WAL_EXCLUSIVE_MODE  1     
................................................................................
*/
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  */
  int 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
................................................................................
    }
    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)) ){
................................................................................
  /* 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 ) mxFrame = pWal->pSnapshot->mxFrame;
#endif
  for(i=1; i<WAL_NREADER; i++){
    u32 thisMark = pInfo->aReadMark[i];
    if( mxReadMark<=thisMark && thisMark<=mxFrame ){
      assert( thisMark!=READMARK_NOT_USED );
      mxReadMark = thisMark;
      mxI = i;
    }
  }
  /* There was once an "if" here. The extra "{" is to preserve indentation. */
  {
    if( (pWal->readOnly & WAL_SHM_RDONLY)==0
     && (mxReadMark<mxFrame || mxI==0)
    ){
      for(i=1; i<WAL_NREADER; i++){
        rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
        if( rc==SQLITE_OK ){
          mxReadMark = pInfo->aReadMark[i] = mxFrame;
          mxI = i;
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
          break;
        }else if( rc!=SQLITE_BUSY ){
          return rc;
        }
      }
................................................................................
** 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))){
    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)) ){
      volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
      rc = walLockShared(pWal, WAL_READ_LOCK(0));
      if( rc==SQLITE_OK ){
        if( pInfo->nBackfill<=pSnapshot->mxFrame 
         && pSnapshot->aSalt[0]==pWal->hdr.aSalt[0]
         && pSnapshot->aSalt[1]==pWal->hdr.aSalt[1]
        ){
          assert( pWal->readLock>0 );
          assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame );
          memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr));
          *pChanged = bChanged;
        }else{
          rc = SQLITE_BUSY_SNAPSHOT;
        }
        walUnlockShared(pWal, WAL_READ_LOCK(0));
      }
      if( rc!=SQLITE_OK ){
        sqlite3WalEndReadTransaction(pWal);
      }
    }
  }
#endif
  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
................................................................................
** 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
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;
  }else{
    memcpy(pRet, &pWal->hdr, sizeof(WalIndexHdr));
    *ppSnapshot = (sqlite3_snapshot*)pRet;
  }

  return rc;
}

void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot){
  pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
}
#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

#endif /* #ifndef SQLITE_OMIT_WAL */

Changes to src/wal.h.

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int sqlite3WalExclusiveMode(Wal *pWal, int op);

/* 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);






#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */







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int sqlite3WalExclusiveMode(Wal *pWal, int op);

/* 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);

#ifdef SQLITE_ENABLE_SNAPSHOT
int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot);
void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot);
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */