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https://issues.apache.org/jira/browse/LUCENE-5696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14006394#comment-14006394
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Uwe Schindler commented on LUCENE-5696:
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bq. If the point of the weak hash table was to manage memory, maybe Lucene
should also provide a way to have a set of CachingWrapperFilter instances with
bounded memory usage? (probably with the help of LUCENE-5695 that would make
computing RAM consumption cheaper)
Weak references can never be meant to manage memory. This is a common
misunderstanding. The use of wek references here is to remove the hard
reference between the two objects. Indeed its a problem here.
But if you use a IndexReaderClosedListener it may make the problem worse: The
listener has *hard* reference to the CachingWrapperFilter. Nowadays, if you
throw away the CachingWrapper filter, the CachingWrapperFilter is free (as
nothing has a reference anymore to the Filter). But once this one "registers"
itsself to the IndexReader, it has a suddenly a hard reference from IndexReader
to the filter -> oh no! Now you have a leak. You need a weak reference in one
direction to allow the cleanup.
> Remove Weakhashmap from CachingWrapperFilter
> --------------------------------------------
>
> Key: LUCENE-5696
> URL: https://issues.apache.org/jira/browse/LUCENE-5696
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
>
> Filters can take up a good amount of space, I think its terrible this thing
> relies entirely upon weak references.
> Actually I don't think it should use weak references at all, in my opinion,
> it should instead use a ConcurrentHashmap and coreClosedListeners to purge
> things.
> We already ensure and test since LUCENE-5553 that these listeners are always
> fired on close, even under exceptional cases, so I don't understand why we
> need weak references anywhere.
> So maybe the fix is to just move up coreClosedListener to AtomicReader? And
> maybe nuke getCoreCacheKey and getCombinedCoreAndDeletesKey.
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