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Posted to dev@lucene.apache.org by "David Smiley (JIRA)" <ji...@apache.org> on 2014/03/16 05:48:48 UTC
[jira] [Updated] (LUCENE-3425) NRT Caching Dir to allow for exact
memory usage, better buffer allocation and "global" cross indices control
[ https://issues.apache.org/jira/browse/LUCENE-3425?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
David Smiley updated LUCENE-3425:
---------------------------------
Fix Version/s: (was: 4.7)
4.8
> 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: 4.8
>
>
> 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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