[FLINK-14997] Avoid to call unnecessary delete within RocksDBState's mergeNamespaces implementation

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.10.0
• Component/s: Runtime / State Backends
• Labels: pull-request-available
• Assignee: Yun Tang
• Reporter: Yun Tang
• Created: 01/Dec/19 16:16
• Updated: 04/Dec/19 14:08
• Resolved: 04/Dec/19 14:08

Description

After FLINK-7700, we delete old state when merging namespaces of RocksDB state. However, this change still leaves some performance space to improve:

byte[] valueBytes = backend.db.get(columnFamily, sourceKey);
backend.db.delete(columnFamily, writeOptions, sourceKey);

if (valueBytes != null) {
   backend.db.merge(columnFamily, writeOptions, targetKey, valueBytes);
}

As you can see, we would call delete instantly after we get the valueBytes. However, since we did not allow null in list state value and the delete operation could be removed to the statement block which has verified the valueBytes is not null. By doing this, we could avoid unnecessary delete calls if sourceKey not existed actually.

Issue Links

• links to: GitHub Pull Request #10383