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https://issues.apache.org/jira/browse/LUCENE-2135?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12787659#action_12787659
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Christian Kohlschütter commented on LUCENE-2135:
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Honestly, please have a look at LUCENE-2133, I really think it is a good
starting point to solve all these problems. Could we perhaps merge the two
issues (LUCENE-2133 and LUCENE-2135)?
A quick summary of LUCENE-2133:
The patch allows one or more IndexReaders to share common cache information
(whatever this is), stored in the same "IndexCache" instance. The IndexCache is
designed to contain *any* cacheable/volatile information that can be
regenerated from the IndexReader.
For example: all clones of SegmentReader share the same SegmentReaderIndexCache
with the original instance, containing the ThreadLocals of the "core reader".
By default (for all IndexReader classes) the IndexCache provides access to the
"IndexFieldCache" (a non-static reimplementation of FieldCache).
To provide arbitrary cacheable objects we could now extend IndexCache by a
simple HashMap (it does not need to be a WeakHashMap, since the IndexCache is
closed and purged as soon as the original IndexReader is closed).
If you wish so, with the help of IndexCache we might even easily implement two
different field caches for the same IndexCache instance, one that changes with
deleted docs and another one that does not. Basically we may add any other kind
of cache at a later point *without* touching IndexReader again. To re-use
Earwin Burrfoot statement from above, that would then *not* "complicate
IndexReader beyond that unholy mess it already is."
> IndexReader.close should forcefully evict entries from FieldCache
> -----------------------------------------------------------------
>
> Key: LUCENE-2135
> URL: https://issues.apache.org/jira/browse/LUCENE-2135
> Project: Lucene - Java
> Issue Type: Bug
> Components: Index
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 3.1
>
> Attachments: LUCENE-2135.patch, LUCENE-2135.patch
>
>
> Spinoff of java-user thread "heap memory issues when sorting by a string
> field".
> We rely on WeakHashMap to hold our FieldCache, keyed by reader. But this
> lacks immediacy on releasing the reference, after a reader is closed.
> WeakHashMap can't free the key until the reader is no longer referenced by
> the app. And, apparently, WeakHashMap has a further impl detail that requires
> invoking one of its methods for it to notice that a key has just become only
> weakly reachable.
> To fix this, I think on IR.close we should evict entries from the FieldCache,
> as long as the sub-readers are truly closed (refCount dropped to 0).
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