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https://issues.apache.org/jira/browse/LUCENE-3425?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13765217#comment-13765217
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caviler commented on LUCENE-3425:
---------------------------------
Actually, in my case, using NRTCachingDir always causes OutOfMemory error!
after it happened, we analysed a gc.hprof file by Eclipse MAT, we believe that:
core segment reader will hold a big size of RAMFile instance that created by
NRTCachingDir.createOutput,
if core segment reader not merged or closed, those RAMFile instances will use
more and more buffer,
but never have chance to uncache from NRTCachingDir instance,
so, when all segment reader allocated buffer size is bigger than we have, it
will causes OutOfMemory error!
> NRT Caching Dir to allow for exact memory usage, better buffer allocation and
> "global" cross indices control
> ------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-3425
> URL: https://issues.apache.org/jira/browse/LUCENE-3425
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/index
> Affects Versions: 3.4, 4.0-ALPHA
> Reporter: Shay Banon
> Fix For: 5.0, 4.5
>
>
> A discussion on IRC raised several improvements that can be made to NRT
> caching dir. Some of the problems it currently has are:
> 1. Not explicitly controlling the memory usage, which can result in overusing
> memory (for example, large new segments being committed because refreshing is
> too far behind).
> 2. Heap fragmentation because of constant allocation of (probably promoted to
> old gen) byte buffers.
> 3. Not being able to control the memory usage across indices for multi index
> usage within a single JVM.
> A suggested solution (which still needs to be ironed out) is to have a
> BufferAllocator that controls allocation of byte[], and allow to return
> unused byte[] to it. It will have a cap on the size of memory it allows to be
> allocated.
> The NRT caching dir will use the allocator, which can either be provided (for
> usage across several indices) or created internally. The caching dir will
> also create a wrapped IndexOutput, that will flush to the main dir if the
> allocator can no longer provide byte[] (exhausted).
> When a file is "flushed" from the cache to the main directory, it will return
> all the currently allocated byte[] to the BufferAllocator to be reused by
> other "files".
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