[GitHub] flink pull request #3801: [FLINK-6364] [checkpoints] Implement incremental c...

[gyfora <gi...@git.apache.org>]

Github user gyfora commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3801#discussion_r114270508
  
    --- Diff: flink-contrib/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBKeyedStateBackend.java ---
    @@ -621,6 +692,237 @@ private static void checkInterrupted() throws InterruptedException {
     		}
     	}
     
    +	private static class RocksDBIncrementalSnapshotOperation {
    +
    +		private final RocksDBKeyedStateBackend<?> stateBackend;
    +
    +		private final CheckpointStreamFactory checkpointStreamFactory;
    +
    +		private final long checkpointId;
    +
    +		private final long checkpointTimestamp;
    +
    +		private Map<String, StreamStateHandle> baseSstFiles;
    +
    +		private List<KeyedBackendSerializationProxy.StateMetaInfo<?, ?>> stateMetaInfos = new ArrayList<>();
    +
    +		private FileSystem backupFileSystem;
    +		private Path backupPath;
    +
    +		private FSDataInputStream inputStream = null;
    +		private CheckpointStreamFactory.CheckpointStateOutputStream outputStream = null;
    +
    +		// new sst files since the last completed checkpoint
    +		private Set<String> newSstFileNames = new HashSet<>();
    +
    +		// handles to the sst files in the current snapshot
    +		private Map<String, StreamStateHandle> sstFiles = new HashMap<>();
    +
    +		// handles to the misc files in the current snapshot
    +		private Map<String, StreamStateHandle> miscFiles = new HashMap<>();
    +
    +		private StreamStateHandle metaStateHandle = null;
    +
    +		private RocksDBIncrementalSnapshotOperation(
    +				RocksDBKeyedStateBackend<?> stateBackend,
    +				CheckpointStreamFactory checkpointStreamFactory,
    +				long checkpointId,
    +				long checkpointTimestamp) {
    +
    +			this.stateBackend = stateBackend;
    +			this.checkpointStreamFactory = checkpointStreamFactory;
    +			this.checkpointId = checkpointId;
    +			this.checkpointTimestamp = checkpointTimestamp;
    +		}
    +
    +		private StreamStateHandle materializeStateData(Path filePath) throws Exception {
    +			try {
    +				final byte[] buffer = new byte[1024];
    +
    +				FileSystem backupFileSystem = backupPath.getFileSystem();
    +				inputStream = backupFileSystem.open(filePath);
    +				stateBackend.cancelStreamRegistry.registerClosable(inputStream);
    +
    +				outputStream = checkpointStreamFactory
    +					.createCheckpointStateOutputStream(checkpointId, checkpointTimestamp);
    +				stateBackend.cancelStreamRegistry.registerClosable(outputStream);
    +
    +				while (true) {
    +					int numBytes = inputStream.read(buffer);
    +
    +					if (numBytes == -1) {
    +						break;
    +					}
    +
    +					outputStream.write(buffer, 0, numBytes);
    +				}
    +
    +				return outputStream.closeAndGetHandle();
    +			} finally {
    +				if (inputStream != null) {
    +					stateBackend.cancelStreamRegistry.unregisterClosable(inputStream);
    +					inputStream.close();
    +					inputStream = null;
    +				}
    +
    +				if (outputStream != null) {
    +					stateBackend.cancelStreamRegistry.unregisterClosable(outputStream);
    +					outputStream.close();
    +					outputStream = null;
    +				}
    +			}
    +		}
    +
    +		private StreamStateHandle materializeMetaData() throws Exception {
    +			try {
    +				outputStream = checkpointStreamFactory
    +					.createCheckpointStateOutputStream(checkpointId, checkpointTimestamp);
    +				stateBackend.cancelStreamRegistry.registerClosable(outputStream);
    +
    +				KeyedBackendSerializationProxy serializationProxy =
    +					new KeyedBackendSerializationProxy(stateBackend.keySerializer, stateMetaInfos);
    +				DataOutputView out = new DataOutputViewStreamWrapper(outputStream);
    +
    +				serializationProxy.write(out);
    +
    +				return outputStream.closeAndGetHandle();
    +			} finally {
    +				if (outputStream != null) {
    +					stateBackend.cancelStreamRegistry.unregisterClosable(outputStream);
    +					outputStream.close();
    +					outputStream = null;
    +				}
    +			}
    +		}
    +
    +		void takeSnapshot() throws Exception {
    +			// use the last completed checkpoint as the comparison base.
    +			baseSstFiles = stateBackend.materializedSstFiles.get(stateBackend.lastCompletedCheckpointId);
    +
    +			// save meta data
    +			for (Map.Entry<String, Tuple2<ColumnFamilyHandle, RegisteredBackendStateMetaInfo<?, ?>>> stateMetaInfoEntry : stateBackend.kvStateInformation.entrySet()) {
    +
    +				RegisteredBackendStateMetaInfo<?, ?> metaInfo = stateMetaInfoEntry.getValue().f1;
    +
    +				KeyedBackendSerializationProxy.StateMetaInfo<?, ?> metaInfoProxy =
    +					new KeyedBackendSerializationProxy.StateMetaInfo<>(
    +						metaInfo.getStateType(),
    +						metaInfo.getName(),
    +						metaInfo.getNamespaceSerializer(),
    +						metaInfo.getStateSerializer());
    +
    +				stateMetaInfos.add(metaInfoProxy);
    +			}
    +
    +			// save state data
    +			backupPath = new Path(stateBackend.instanceBasePath.getAbsolutePath(), "chk-" + checkpointId);
    +			backupFileSystem = backupPath.getFileSystem();
    +			if (backupFileSystem.exists(backupPath)) {
    +				LOG.warn("Deleting an existing local checkpoint directory " +
    +					backupPath + ".");
    +
    +				backupFileSystem.delete(backupPath, true);
    +			}
    +
    +			// create hard links of living files in the checkpoint path
    +			Checkpoint checkpoint = Checkpoint.create(stateBackend.db);
    +			checkpoint.createCheckpoint(backupPath.getPath());
    --- End diff --
    
    I guess this will also create the sst file(s) for the current changes (that are in the log). I wonder if this will lead to too many sst files for small snapshot intervals after a while.


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