Github user sihuazhou commented on a diff in the pull request:
https://github.com/apache/flink/pull/5582#discussion_r192076835
--- Diff:
flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBKeyedStateBackend.java
---
@@ -791,20 +784,215 @@ private void restoreInstance(
}
/**
- * Recovery from local incremental state.
+ * Recovery from multi incremental states.
+ * In case of rescaling, this method creates a temporary
RocksDB instance for a key-groups shard. All contents
+ * from the temporary instance are copied into the real restore
instance and then the temporary instance is
+ * discarded.
*/
- private void restoreInstance(IncrementalLocalKeyedStateHandle
localKeyedStateHandle) throws Exception {
+ void restoreFromMultiHandles(Collection<KeyedStateHandle>
restoreStateHandles) throws Exception {
+
+ KeyGroupRange targetKeyGroupRange =
stateBackend.keyGroupRange;
+
+ chooseTheBestStateHandleToInit(restoreStateHandles,
targetKeyGroupRange);
+
+ int targetStartKeyGroup =
stateBackend.getKeyGroupRange().getStartKeyGroup();
+ byte[] targetStartKeyGroupPrefixBytes = new
byte[stateBackend.keyGroupPrefixBytes];
+ for (int j = 0; j < stateBackend.keyGroupPrefixBytes;
++j) {
+ targetStartKeyGroupPrefixBytes[j] = (byte)
(targetStartKeyGroup >>> ((stateBackend.keyGroupPrefixBytes - j - 1) *
Byte.SIZE));
+ }
+
+ for (KeyedStateHandle rawStateHandle :
restoreStateHandles) {
+
+ if (!(rawStateHandle instanceof
IncrementalKeyedStateHandle)) {
+ throw new
IllegalStateException("Unexpected state handle type, " +
+ "expected " +
IncrementalKeyedStateHandle.class +
+ ", but found " +
rawStateHandle.getClass());
+ }
+
+ Path temporaryRestoreInstancePath = new
Path(stateBackend.instanceBasePath.getAbsolutePath() +
UUID.randomUUID().toString());
+ try (RestoredDBInfo tmpRestoreDBInfo =
restoreDBFromStateHandle(
+ (IncrementalKeyedStateHandle)
rawStateHandle,
+ temporaryRestoreInstancePath,
+ targetKeyGroupRange,
+
stateBackend.keyGroupPrefixBytes)) {
+
+ List<ColumnFamilyDescriptor>
tmpColumnFamilyDescriptors = tmpRestoreDBInfo.columnFamilyDescriptors;
+ List<ColumnFamilyHandle>
tmpColumnFamilyHandles = tmpRestoreDBInfo.columnFamilyHandles;
+
+ // iterating only the requested
descriptors automatically skips the default column family handle
+ for (int i = 0; i <
tmpColumnFamilyDescriptors.size(); ++i) {
+ ColumnFamilyHandle
tmpColumnFamilyHandle = tmpColumnFamilyHandles.get(i);
+ ColumnFamilyDescriptor
tmpColumnFamilyDescriptor = tmpColumnFamilyDescriptors.get(i);
+
+ ColumnFamilyHandle
targetColumnFamilyHandle = getOrRegisterColumnFamilyHandle(
+
tmpColumnFamilyDescriptor, null,
tmpRestoreDBInfo.stateMetaInfoSnapshots.get(i));
+
+ try (RocksIterator iterator =
tmpRestoreDBInfo.db.newIterator(tmpColumnFamilyHandle)) {
+
+
iterator.seek(targetStartKeyGroupPrefixBytes);
--- End diff --
I think this is a not so nice API of `RocksIterator`, a newly created
Iterator doesn't point to the header element by default, users need to
performance the `seek()` to make sure it is valid.
---
