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https://issues.apache.org/jira/browse/KAFKA-8094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16790070#comment-16790070
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Sophie Blee-Goldman commented on KAFKA-8094:
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After some investigation, the solution is not as straightforward as simply
replacing TreeMap -> ConcurrentSkipListMap and using a subMap iterator.
Iterators are only weakly consistent, and changes to the underlying map are not
guaranteed to be reflected in the iterator. Implementing it this way may cause,
for example, evicted entries to still be returned by the iterator (see
ThreadCacheTest#shouldSkipEntriesWhereValueHasBeenEvictedFromCache)
> Iterating over cache with get(key) is inefficient
> --------------------------------------------------
>
> Key: KAFKA-8094
> URL: https://issues.apache.org/jira/browse/KAFKA-8094
> Project: Kafka
> Issue Type: Improvement
> Reporter: Sophie Blee-Goldman
> Priority: Major
> Labels: streams
>
> Currently, range queries in the caching layer are implemented by creating an
> iterator over the subset of keys in the range, and calling get() on the
> underlying TreeMap for each key. While this protects against
> ConcurrentModificationException, we can improve performance by replacing the
> TreeMap with a concurrent data structure such as ConcurrentSkipListMap and
> then just iterating over a subMap.
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