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

["Yun Tang (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-14997?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16985595#comment-16985595 ] 

Yun Tang commented on FLINK-14997:
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[~aljoscha], [~azagrebin] what do you think of this improvement? Please assign to me if possible.

> 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
>            Priority: Minor
>             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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