assert( pWal->nWiData>0 && pWal->apWiData[0] );

  /* Take WAL_READ_LOCK(0). This has the effect of preventing any
  ** live clients from running a checkpoint, but does not stop them
  ** from running recovery.  */
  rc = walLockShared(pWal, WAL_READ_LOCK(0));
  if( rc!=SQLITE_OK ){
    return (rc==SQLITE_BUSY ? WAL_RETRY : rc);

  }
  pWal->readLock = 0;

  /* Try to map the *-shm file again. If it succeeds this time, then 
  ** a non-readonly_shm connection has already connected to the database.
  ** In this case, start over with opening the transaction.
  ** 
................................................................................
    assert( rc!=SQLITE_OK );
    rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc);
    goto begin_unlocked_out;
  }

  memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr));
  rc = sqlite3OsFileSize(pWal->pWalFd, &szWal);
  if( rc!=SQLITE_OK || (szWal<WAL_HDRSIZE && pWal->hdr.mxFrame==0) ){



    /* If the wal file is too small to contain a wal-header and the
    ** wal-index header has mxFrame==0, then it must be safe to proceed
    ** reading the database file only. However, the page cache cannot
    ** be trusted, as a read/write connection may have connected, written
    ** the db, run a checkpoint, truncated the wal file and disconnected
    ** since this client's last read transaction.  */
    *pChanged = 1;

    goto begin_unlocked_out;
  }

  /* Check the salt keys at the start of the wal file still match. */
  rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
  if( rc!=SQLITE_OK ){
    goto begin_unlocked_out;
................................................................................
      iOffset+=szFrame
  ){
    u32 pgno;                   /* Database page number for frame */
    u32 nTruncate;              /* dbsize field from frame header */

    /* Read and decode the next log frame. */
    rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
    if( rc!=SQLITE_OK ){
      if( rc==SQLITE_IOERR_SHORT_READ ){
        /* If this branch is taken, some other client has truncated the
        ** *-wal file since the call to sqlite3OsFileSize() above. This
        ** indicates that a read-write client has connected to the system.
        ** So retry opening this read transaction.  */
        rc = WAL_RETRY;
      }
      break;
    }
    if( !walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame) ) break;

    /* If nTruncate is non-zero, then a complete transaction has been
    ** appended to this wal file. Set rc to WAL_RETRY and break out of
    ** the loop.  */
    if( nTruncate ){
      rc = WAL_RETRY;

  assert( pWal->nWiData>0 && pWal->apWiData[0] );

  /* Take WAL_READ_LOCK(0). This has the effect of preventing any
  ** live clients from running a checkpoint, but does not stop them
  ** from running recovery.  */
  rc = walLockShared(pWal, WAL_READ_LOCK(0));
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_BUSY ) rc = WAL_RETRY;
    goto begin_unlocked_out;
  }
  pWal->readLock = 0;

  /* Try to map the *-shm file again. If it succeeds this time, then 
  ** a non-readonly_shm connection has already connected to the database.
  ** In this case, start over with opening the transaction.
  ** 
................................................................................
    assert( rc!=SQLITE_OK );
    rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc);
    goto begin_unlocked_out;
  }

  memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr));
  rc = sqlite3OsFileSize(pWal->pWalFd, &szWal);
  if( rc!=SQLITE_OK ){
    goto begin_unlocked_out;
  }
  if( szWal<WAL_HDRSIZE ){
    /* If the wal file is too small to contain a wal-header and the
    ** wal-index header has mxFrame==0, then it must be safe to proceed
    ** reading the database file only. However, the page cache cannot
    ** be trusted, as a read/write connection may have connected, written
    ** the db, run a checkpoint, truncated the wal file and disconnected
    ** since this client's last read transaction.  */
    *pChanged = 1;
    rc = (pWal->hdr.mxFrame==0 ? SQLITE_OK : WAL_RETRY);
    goto begin_unlocked_out;
  }

  /* Check the salt keys at the start of the wal file still match. */
  rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
  if( rc!=SQLITE_OK ){
    goto begin_unlocked_out;
................................................................................
      iOffset+=szFrame
  ){
    u32 pgno;                   /* Database page number for frame */
    u32 nTruncate;              /* dbsize field from frame header */

    /* Read and decode the next log frame. */
    rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
    if( rc!=SQLITE_OK ) break;









    if( !walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame) ) break;

    /* If nTruncate is non-zero, then a complete transaction has been
    ** appended to this wal file. Set rc to WAL_RETRY and break out of
    ** the loop.  */
    if( nTruncate ){
      rc = WAL_RETRY;

    }
    code2 { db2 close }
    list [file size test.db-wal] [file size test.db-shm]
  } [list [wal_file_size 4 1024] 32768]
  do_test 3.3.3 {
    sql1 { SELECT * FROM t1 }
  } {i ii}







}







































































































































finish_test

    }
    code2 { db2 close }
    list [file size test.db-wal] [file size test.db-shm]
  } [list [wal_file_size 4 1024] 32768]
  do_test 3.3.3 {
    sql1 { SELECT * FROM t1 }
  } {i ii}

  #-----------------------------------------------------------------------
  #
  #
  catch { code1 { db close } }
  catch { code2 { db2 close } }
  catch { code3 { db3 close } }

  do_test 4.0 {
    code1 { forcedelete test.db }
    code1 { sqlite3 db test.db }
    sql1 {
      PRAGMA journal_mode = wal;
      CREATE TABLE t1(x);
      INSERT INTO t1 VALUES('hello');
      INSERT INTO t1 VALUES('world');
    }

    forcecopy test.db test.db2
    forcecopy test.db-wal test.db2-wal
    forcecopy test.db-shm test.db2-shm
    
    code1 { db close }
  } {}

  do_test 4.1.1 {
    code2 { sqlite3 db2 file:test.db2?readonly_shm=1 }
    sql2 { SELECT * FROM t1 }
  } {hello world}

  do_test 4.1.2 {
    code3 { sqlite3 db3 test.db2 }
    sql3 {
      INSERT INTO t1 VALUES('!');
      PRAGMA wal_checkpoint = truncate;
    }
    code3 { db3 close }
  } {}
  do_test 4.1.3 {
    sql2 { SELECT * FROM t1 }
  } {hello world !}

  catch { code1 { db close } }
  catch { code2 { db2 close } }
  catch { code3 { db3 close } }

  do_test 4.2.1 {
    code1 { sqlite3 db test.db }
    sql1 {
      INSERT INTO t1 VALUES('!');
      INSERT INTO t1 VALUES('!');

      PRAGMA cache_size = 10;
      CREATE TABLE t2(x);

      BEGIN;
        WITH s(i) AS (
          SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<500
          )
        INSERT INTO t2 SELECT randomblob(500) FROM s;
        SELECT count(*) FROM t2;
    } 
  } {500}
  do_test 4.2.2 {
    file size test.db-wal
  } {461152}
  do_test 4.2.4 {
    forcecopy test.db test.db2
    forcecopy test.db-wal test.db2-wal
    forcecopy test.db-shm test.db2-shm

    code2 { sqlite3 db2 file:test.db2?readonly_shm=1 }
    sql2 {
      SELECT * FROM t1;
      SELECT count(*) FROM t2;
    }
  } {hello world ! ! 0}

  #-----------------------------------------------------------------------
  #
  #
  catch { code1 { db close } }
  catch { code2 { db2 close } }
  catch { code3 { db3 close } }

  do_test 5.0 {
    code1 { forcedelete test.db }
    code1 { sqlite3 db test.db }
    sql1 {
      PRAGMA journal_mode = wal;
      CREATE TABLE t1(x);
      INSERT INTO t1 VALUES('hello');
      INSERT INTO t1 VALUES('world');
      INSERT INTO t1 VALUES('!');
      INSERT INTO t1 VALUES('world');
      INSERT INTO t1 VALUES('hello');
    }

    forcecopy test.db test.db2
    forcecopy test.db-wal test.db2-wal
    forcecopy test.db-shm test.db2-shm
    
    code1 { db close }
  } {}

  do_test 5.1 {
    code2 { sqlite3 db2 file:test.db2?readonly_shm=1 }
    sql2 {
      SELECT * FROM t1;
    }
  } {hello world ! world hello}

  do_test 5.2 {
    code1 {
      proc handle_read {op args} {
        if {$op=="xRead" && [file tail [lindex $args 0]]=="test.db2-wal"} {
          set ::res2 [sql2 { SELECT * FROM t1 }]
        }
        puts "$msg xRead $args"
        return "SQLITE_OK"
      }
      testvfs tvfs -fullshm 1

      sqlite3 db file:test.db2?vfs=tvfs
      db eval { SELECT * FROM sqlite_master }

      tvfs filter xRead
      tvfs script handle_read
    }
    sql1 {
      PRAGMA wal_checkpoint = truncate;
    }
    code1 { set ::res2 }
  } {hello world ! world hello}

  do_test 5.3 {
    code1 { db close }
    code1 { tvfs delete }
  } {}


}

finish_test