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https://issues.apache.org/jira/browse/KAFKA-9356?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17017748#comment-17017748
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Sophie Blee-Goldman commented on KAFKA-9356:
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As [~bchen225242] said, Streams is single writer so this should not cause any
problems. I'm going to close this bug as "Not a Problem"
It's worth noting that it might be a good idea to switch to TreeMap for
different reasons. Right now the ConcurrentSkipListMap allows us to safely
perform range queries without copying over the entire keyset, but the
performance on point queries seems to scale noticeably worse with the number of
unique keys. Point queries are used by aggregations while range queries are
used by windowed joins, but of course both are available within the PAPI and
for interactive queries so it's hard to say which we should prefer. Maybe
rather than make that tradeoff we should have one version for efficient range
queries (a "JoinWindowStore") and one for efficient point queries
("AggWindowStore") – or something. I know we've had similar thoughts for a
different RocksDB store layout for Joins (although I can't find that ticket
anywhere..), it seems like the in-memory stores could benefit from a special
"Join" version as well cc/ [~guozhang]
> Potential data loss in InMemoryWindowStore and InMemorySessionStore
> -------------------------------------------------------------------
>
> Key: KAFKA-9356
> URL: https://issues.apache.org/jira/browse/KAFKA-9356
> Project: Kafka
> Issue Type: Bug
> Reporter: Roman Leventov
> Priority: Major
>
> {{InMemoryWindowStore.put()}} and {{InMemorySessionStore.put()}} call
> {{computeIfAbsent()}} method on {{ConcurrentSkipListMap}} objects which opens
> up possibility for data loss because
> {{ConcurrentSkipListMap.computeIfAbsent()}} is not an atomic operation.
> Possible fix: replace {{ConcurrentSkipListMaps with synchronized[Sorted,
> Navigable]Map(new TreeMap<>())}}.
>
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