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https://issues.apache.org/jira/browse/FLINK-21413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17287600#comment-17287600
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Jiayi Liao commented on FLINK-21413:
------------------------------------
Sure. I'm still thinking about the solution. I've come up with two proposals:
1. #TtlMapState#getUnexpiredOrNull returns null directly if the
{{unexpired.size() == 0}}, but this will also clean the empty map.
2. Add a lastAccessTimestamp(long) in #TtlMapState like what Flink does in
TtlValue, and use the timestamp to check the map's lifecyle. But this may break
the state compatibility.
What do you think? [~liyu]
> TtlMapState and TtlListState cannot be clean completely with Filesystem
> StateBackend
> ------------------------------------------------------------------------------------
>
> Key: FLINK-21413
> URL: https://issues.apache.org/jira/browse/FLINK-21413
> Project: Flink
> Issue Type: Bug
> Components: Runtime / State Backends
> Affects Versions: 1.9.0
> Reporter: Jiayi Liao
> Priority: Major
> Attachments: image-2021-02-19-11-13-58-672.png
>
>
> Take the #TtlMapState as an example,
>
> {code:java}
> public Map<UK, TtlValue<UV>> getUnexpiredOrNull(@Nonnull Map<UK,
> TtlValue<UV>> ttlValue) {
> Map<UK, TtlValue<UV>> unexpired = new HashMap<>();
> TypeSerializer<TtlValue<UV>> valueSerializer =
> ((MapSerializer<UK, TtlValue<UV>>)
> original.getValueSerializer()).getValueSerializer();
> for (Map.Entry<UK, TtlValue<UV>> e : ttlValue.entrySet()) {
> if (!expired(e.getValue())) {
> // we have to do the defensive copy to update the
> value
> unexpired.put(e.getKey(),
> valueSerializer.copy(e.getValue()));
> }
> }
> return ttlValue.size() == unexpired.size() ? ttlValue : unexpired;
> }
> {code}
>
> The returned value will never be null and the #StateEntry will exists
> forever, which leads to memory leak if the key's range of the stream is very
> large. Below we can see that 20+ millison uncleared TtlStateMap could take up
> several GB memory.
>
> !image-2021-02-19-11-13-58-672.png!
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