Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/3801#discussion_r114283114
--- 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 --
@gyfora I think your initial concerns are valid. We need to flush the
memtable to disk prior to a checkpoint and this will generate a SST. What is
required for fast checkpoint intervals is an alternative mechanism to quickly
determine a delta from the previous incremental checkpoint. This could be a
changelog buffer in Flink that we maintain up to a certain size. The content
becomes part of the private state in the incremental snapshot and it is dropped
i) after each checkpoint or ii) after exceeding a certain size which to justify
writing a new SST.
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