SQLite

          rc = sqlite3BtreeBeginTrans(pBt, 0);
          sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), 0);
        }
      }
    }
  }

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

/*
** Recover as many snapshots as possible from the wal file associated with
** schema zDb of database db.
*/
int sqlite3_snapshot_recover(sqlite3 *db, const char *zDb){
  int rc = SQLITE_ERROR;
  int iDb;
#ifndef SQLITE_OMIT_WAL

#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) ){
      rc = sqlite3PagerSnapshotRecover(sqlite3BtreePager(pBt));
    }
  }
  sqlite3_mutex_leave(db->mutex);
#endif   /* SQLITE_OMIT_WAL */
  return rc;
}

/*
** Free a snapshot handle obtained from sqlite3_snapshot_get().

  if( pPager->pWal ){
    sqlite3WalSnapshotOpen(pPager->pWal, pSnapshot);
  }else{
    rc = SQLITE_ERROR;
  }
  return rc;
}

/*
** If this is a WAL database, call sqlite3WalSnapshotRecover(). If this 
** is not a WAL database, return an error.
*/
int sqlite3PagerSnapshotRecover(Pager *pPager){
  int rc;
  if( pPager->pWal ){
    rc = sqlite3WalSnapshotRecover(pPager->pWal);
  }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

  int sqlite3PagerWalCallback(Pager *pPager);
  int sqlite3PagerOpenWal(Pager *pPager, int *pisOpen);
  int sqlite3PagerCloseWal(Pager *pPager, sqlite3*);
  int sqlite3PagerUseWal(Pager *pPager);
# ifdef SQLITE_ENABLE_SNAPSHOT
  int sqlite3PagerSnapshotGet(Pager *pPager, sqlite3_snapshot **ppSnapshot);
  int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot);
  int sqlite3PagerSnapshotRecover(Pager *pPager);
# endif
#else
# define sqlite3PagerUseWal(x) 0
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);

** snapshot, and a positive value if P1 is a newer snapshot than P2.
*/
SQLITE_EXPERIMENTAL int sqlite3_snapshot_cmp(
  sqlite3_snapshot *p1,
  sqlite3_snapshot *p2
);

/*
** CAPI3REF: Recover snapshots from a wal file
** EXPERIMENTAL
*/
SQLITE_EXPERIMENTAL int sqlite3_snapshot_recover(sqlite3 *db, const char *zDb);

/*
** 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

    if( sqlite3TestMakePointerStr(interp, zBuf, pSnapshot) ) return TCL_ERROR;
    Tcl_SetObjResult(interp, Tcl_NewStringObj(zBuf, -1));
  }
  return TCL_OK;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Usage: sqlite3_snapshot_recover DB DBNAME
*/
static int SQLITE_TCLAPI test_snapshot_recover(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;
  sqlite3 *db;
  char *zName;

  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_recover(db, zName);
  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }else{
    Tcl_ResetResult(interp);
  }
  return TCL_OK;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Usage: sqlite3_snapshot_open DB DBNAME SNAPSHOT
*/
static int SQLITE_TCLAPI test_snapshot_open(
  void * clientData,
  Tcl_Interp *interp,

#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 },
     { "sqlite3_snapshot_cmp", test_snapshot_cmp, 0 },
     { "sqlite3_snapshot_recover", test_snapshot_recover, 0 },
     { "sqlite3_snapshot_get_blob", test_snapshot_get_blob, 0 },
     { "sqlite3_snapshot_open_blob", test_snapshot_open_blob, 0 },
     { "sqlite3_snapshot_cmp_blob", test_snapshot_cmp_blob, 0 },
#endif
     { "sqlite3_delete_database", test_delete_database, 0 },
  };
  static int bitmask_size = sizeof(Bitmask)*8;

    return WAL_RETRY;
  }else{
    assert( mxReadMark<=pWal->hdr.mxFrame );
    pWal->readLock = (i16)mxI;
  }
  return rc;
}

/*
** Recover as many snapshots as possible from the wal file.
*/
int sqlite3WalSnapshotRecover(Wal *pWal){
  int dummy;
  int rc;

  rc = sqlite3WalBeginReadTransaction(pWal, &dummy);
  if( rc==SQLITE_OK ){
    rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
    if( rc==SQLITE_OK ){
      volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
      int szPage = (int)pWal->szPage;
      void *pBuf1 = sqlite3_malloc(szPage);
      void *pBuf2 = sqlite3_malloc(szPage);

      if( pBuf1==0 || pBuf2==0 ){
        rc = SQLITE_NOMEM;
      }else{
        u32 i = pInfo->nBackfillAttempted;
        for(i=pInfo->nBackfillAttempted; i>pInfo->nBackfill; i--){
          volatile ht_slot *dummy;
          volatile u32 *aPgno;      /* Array of page numbers */
          u32 iZero;                /* Frame corresponding to aPgno[0] */
          u32 pgno;                 /* Page number in db file */
          i64 iDbOff;               /* Offset of db file entry */
          i64 iWalOff;              /* Offset of wal file entry */
          rc = walHashGet(pWal, walFramePage(i), &dummy, &aPgno, &iZero);

          if( rc==SQLITE_OK ){
            pgno = aPgno[i-iZero];
            iDbOff = (i64)(pgno-1) * szPage;
            iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
            rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
          }

          if( rc==SQLITE_OK ){
            rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
          }

          if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
            break;
          }

          pInfo->nBackfillAttempted = i-1;
        }
      }

      sqlite3_free(pBuf1);
      sqlite3_free(pBuf2);
      walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
    }

    sqlite3WalEndReadTransaction(pWal);
  }

  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.

      /* 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.  
      **
      ** TODO: Does the aReadMark[] lock prevent a checkpointer from doing
      **       this already?
      */
      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

** 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);
int sqlite3WalSnapshotRecover(Wal *pWal);
#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);

  execsql { INSERT INTO t1 VALUES(10, 11, 12) } db2
  execsql BEGIN
  string length [sqlite3_snapshot_get_blob db main]
} 48
execsql COMMIT
db2 close

#-------------------------------------------------------------------------
#
reset_db
do_execsql_test 2.0 {
  CREATE TABLE t1(x);
  PRAGMA journal_mode = wal;
  INSERT INTO t1 VALUES(1);
  INSERT INTO t1 VALUES(2);
} {wal}

do_test 2.1 {
  db trans { set snap [sqlite3_snapshot_get_blob db main] }
  sqlite3_db_config db NO_CKPT_ON_CLOSE 1
  db close
  sqlite3 db test.db

  execsql {SELECT * FROM sqlite_master}
  execsql BEGIN
  sqlite3_snapshot_open_blob db main $snap
  execsql COMMIT;
  execsql { INSERT INTO t1 VALUES(3); }
} {}

do_test 2.2 {
  sqlite3_db_config db NO_CKPT_ON_CLOSE 1
  db close
  sqlite3 db test.db

  execsql {SELECT * FROM sqlite_master}
  execsql BEGIN
  list [catch { sqlite3_snapshot_open_blob db main $snap } msg] $msg
} {1 SQLITE_BUSY_SNAPSHOT}

do_test 2.3 {
  execsql COMMIT
  sqlite3_snapshot_recover db main
  execsql BEGIN
  sqlite3_snapshot_open_blob db main $snap
  execsql { SELECT * FROM t1 }
} {1 2}

do_test 2.4 {
  execsql COMMIT
  execsql { SELECT * FROM t1 }
} {1 2 3}

do_test 2.5 {
  execsql { PRAGMA wal_checkpoint }
  sqlite3_db_config db NO_CKPT_ON_CLOSE 1
  db close
  sqlite3 db test.db

  execsql {SELECT * FROM sqlite_master}
  sqlite3_snapshot_recover db main
  execsql BEGIN
  list [catch { sqlite3_snapshot_open_blob db main $snap } msg] $msg
} {1 SQLITE_BUSY_SNAPSHOT}


finish_test