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

[Shang Yuanchun (Jira)]

Yun Tang created FLINK-14997:
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             Summary: Avoid to call unnecessary delete within RocksDBState's mergeNamespaces implementation
                 Key: FLINK-14997
                 URL: https://issues.apache.org/jira/browse/FLINK-14997
             Project: Flink
          Issue Type: Improvement
          Components: Runtime / State Backends
            Reporter: Yun Tang
             Fix For: 1.10.0


After FLINK-7700, we delete old state when merging namespaces of RocksDB state. However, this change still leaves some performance space to improve:
{code:java}
byte[] valueBytes = backend.db.get(columnFamily, sourceKey);
backend.db.delete(columnFamily, writeOptions, sourceKey);

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



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