[FLINK-29577] Disable rocksdb wal when restore from full snapshot

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Component/s: Runtime / State Backends
• Labels: pull-request-available
• Assignee: Cai Liuyang
• Reporter: Cai Liuyang
• Created: 11/Oct/22 08:26
• Updated: 16/Jun/23 06:11
• Resolved: 18/May/23 07:30

Description

For now, RocksDBFullRestoreOperation and RocksDBHeapTimersFullRestoreOperation does's pass RocksDB::WriteOptions to RocksDBWriteBatchWrapper when restore kv-data, which will use RocksDBWriteBatchWrapper‘s default WriteOptions(doesn't disable rocksdb wal explicitly, see code below), so during restoring from full snapshot, wal is enabled(use more disk and maybe affect rocksdb-write-performance when restoring)

 

// First: RocksDBHeapTimersFullRestoreOperation::restoreKVStateData() doesn't pass WriteOptions to RocksDBWriteBatchWrapper(null as default)

private void restoreKVStateData(
        ThrowingIterator<KeyGroup> keyGroups,
        Map<Integer, ColumnFamilyHandle> columnFamilies,
        Map<Integer, HeapPriorityQueueSnapshotRestoreWrapper<?>> restoredPQStates)
        throws IOException, RocksDBException, StateMigrationException {
    // for all key-groups in the current state handle...
    try (RocksDBWriteBatchWrapper writeBatchWrapper =
            new RocksDBWriteBatchWrapper(this.rocksHandle.getDb(), writeBatchSize)) {
        HeapPriorityQueueSnapshotRestoreWrapper<HeapPriorityQueueElement> restoredPQ = null;
        ColumnFamilyHandle handle = null;
   ......
}


// Second: RocksDBWriteBatchWrapper::flush function doesn't disable wal explicitly when user doesn't pass WriteOptions to RocksDBWriteBatchWrapper
public void flush() throws RocksDBException {
    if (options != null) {
        db.write(options, batch);
    } else {
        // use the default WriteOptions, if wasn't provided.
        try (WriteOptions writeOptions = new WriteOptions()) {
            db.write(writeOptions, batch);
        }
    }
    batch.clear();
}

 

 

As we known, rocksdb's wal is usesless for flink, so i think we can disable wal for RocksDBWriteBatchWrapper's default WriteOptions.

Issue Links

• duplicates: FLINK-32326 Disable WAL in RocksDBWriteBatchWrapper by default
• relates to: FLINK-11138 RocksDB's wal seems to be useless in rocksdb-state-backend that reduce the disk's overhead
• links to: GitHub Pull Request #21015