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Overview
Comment:Avoid locking shm-lock WAL_READ_LOCK(0) during recovery. Doing this allows recovery to proceed while a readonly_shm connection in unlocked mode has an ongoing read transaction.
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SHA3-256:5190d84a296b7cf716ef43bf7b6d4d351ef1a4d650de37dc01a5ab333da7c05d
User & Date: dan 2017-11-02 11:12:03
Context
2017-11-02
18:57
Fix test cases in wal2.test broken by the locking change in the previous commit. check-in: f569c351 user: dan tags: readonly-wal-recovery
11:12
Avoid locking shm-lock WAL_READ_LOCK(0) during recovery. Doing this allows recovery to proceed while a readonly_shm connection in unlocked mode has an ongoing read transaction. check-in: 5190d84a user: dan tags: readonly-wal-recovery
2017-11-01
20:59
If a readonly_shm connection cannot map the *-shm file because no other process is holding the DMS lock, have it read from the database file only, ignoring any content in the wal file. check-in: ce5d13c2 user: dan tags: readonly-wal-recovery
Changes
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Changes to src/wal.c.

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** the necessary locks, this routine returns SQLITE_BUSY.
*/
static int walIndexRecover(Wal *pWal){
  int rc;                         /* Return Code */
  i64 nSize;                      /* Size of log file */
  u32 aFrameCksum[2] = {0, 0};
  int iLock;                      /* Lock offset to lock for checkpoint */
  int nLock;                      /* Number of locks to hold */

  /* Obtain an exclusive lock on all byte in the locking range not already
  ** locked by the caller. The caller is guaranteed to have locked the
  ** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte.
  ** If successful, the same bytes that are locked here are unlocked before
  ** this function returns.
  */
  assert( pWal->ckptLock==1 || pWal->ckptLock==0 );
  assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 );
  assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE );
  assert( pWal->writeLock );
  iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;
  nLock = SQLITE_SHM_NLOCK - iLock;
  rc = walLockExclusive(pWal, iLock, nLock);






  if( rc ){
    return rc;
  }

  WALTRACE(("WAL%p: recovery begin...\n", pWal));

  memset(&pWal->hdr, 0, sizeof(WalIndexHdr));

  rc = sqlite3OsFileSize(pWal->pWalFd, &nSize);
  if( rc!=SQLITE_OK ){
    goto recovery_error;
................................................................................
          pWal->hdr.mxFrame, pWal->zWalName
      );
    }
  }

recovery_error:
  WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
  walUnlockExclusive(pWal, iLock, nLock);

  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){







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** the necessary locks, this routine returns SQLITE_BUSY.
*/
static int walIndexRecover(Wal *pWal){
  int rc;                         /* Return Code */
  i64 nSize;                      /* Size of log file */
  u32 aFrameCksum[2] = {0, 0};
  int iLock;                      /* Lock offset to lock for checkpoint */


  /* Obtain an exclusive lock on all byte in the locking range not already
  ** locked by the caller. The caller is guaranteed to have locked the
  ** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte.
  ** If successful, the same bytes that are locked here are unlocked before
  ** this function returns.
  */
  assert( pWal->ckptLock==1 || pWal->ckptLock==0 );
  assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 );
  assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE );
  assert( pWal->writeLock );
  iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;

  rc = walLockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
  if( rc==SQLITE_OK ){
    rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
    if( rc!=SQLITE_OK ){
      walUnlockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
    }
  }
  if( rc ){
    return rc;
  }

  WALTRACE(("WAL%p: recovery begin...\n", pWal));

  memset(&pWal->hdr, 0, sizeof(WalIndexHdr));

  rc = sqlite3OsFileSize(pWal->pWalFd, &nSize);
  if( rc!=SQLITE_OK ){
    goto recovery_error;
................................................................................
          pWal->hdr.mxFrame, pWal->zWalName
      );
    }
  }

recovery_error:
  WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
  walUnlockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
  walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){

Changes to test/walro2.test.

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    code3 { sqlite3 db3 test.db2 }
    sql3 { SELECT * FROM t1 }
  } {a b c d}

  do_test 1.3.2 {
    sql1 { SELECT * FROM t1 }
  } {a b c d}
































}

finish_test







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    code3 { sqlite3 db3 test.db2 }
    sql3 { SELECT * FROM t1 }
  } {a b c d}

  do_test 1.3.2 {
    sql1 { SELECT * FROM t1 }
  } {a b c d}

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

  do_test 2.1 {
    code2 { sqlite3 db2 test.db }
    sql2 { 
      INSERT INTO t1 VALUES('e', 'f');
      INSERT INTO t1 VALUES('g', 'h');
    }
    file exists test.db-shm
  } {1}

  do_test 2.2 {
    forcecopy test.db test.db2
    forcecopy test.db-wal test.db2-wal
    forcecopy test.db-shm test.db2-shm
    code1 {
      sqlite3 db file:test.db2?readonly_shm=1
    }
    sql1 { 
      BEGIN;
      SELECT * FROM t1;
    }
  } {a b c d}

  do_test 2.3.1 {
    code3 { sqlite3 db3 test.db2 }
    sql3 { SELECT * FROM t1 }
  } {a b c d e f g h}

}

finish_test