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https://issues.apache.org/jira/browse/FLINK-13034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16980707#comment-16980707
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Yu Li commented on FLINK-13034:
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Thanks for the contribution [~yunta]. Mind adding a release note mentioning
about the addition of {{isEmpty}} method in {{MapState}} as per discussed in
[PR|https://github.com/apache/flink/pull/9255#issuecomment-535334308]? Thanks.
> Improve the performance when checking whether mapstate is empty for
> RocksDBStateBackend
> ---------------------------------------------------------------------------------------
>
> Key: FLINK-13034
> URL: https://issues.apache.org/jira/browse/FLINK-13034
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / State Backends
> Affects Versions: 1.6.3, 1.7.2, 1.8.1
> Reporter: Yun Tang
> Assignee: Yun Tang
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.10.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Currently, there existed several scenarios to check whether map state is
> empty in Flink source code,
> e.g.[TemporalRowTimeJoinOperator|https://github.com/apache/flink/blob/8315f38e89f897e32cfa0f23990cb3fb44db0d72/flink-table/flink-table-runtime-blink/src/main/java/org/apache/flink/table/runtime/join/temporal/TemporalRowTimeJoinOperator.java#L192],
> [AbstractRowTimeUnboundedPrecedingOver|#L160)].
> Developers would use below command to check whether the map state is empty:
> {code:java}
> boolean noRecordsToProcess = !inputState.keys().iterator().hasNext();
> {code}
> However, if we use {{RocksDBStateBackend}},
> {{inputState.keys().iterator().hasNext()}} would actually call 1 {{seek}} and
> 128 {{next}} actions in
> [RocksDBMapState|https://github.com/apache/flink/blob/8315f38e89f897e32cfa0f23990cb3fb44db0d72/flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBMapState.java#L483],
> in which the redundant {{next}} actions are not what we want.
> I have two options to improve this:
> * Modify {{RocksDBMapState}} back to previous design which would first load
> one element and then load more elements in the follow-up queries. However,
> this would effect the performance of other map state methods.
> * Add a {{isEmpty()}} method in the public evolving interface {{MapState}},
> so that we could use it to check whether the map state is empty without any
> redundant RocksDB actions.
> I prefer to the 2nd option.
>
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