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https://issues.apache.org/jira/browse/JCR-974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12506599
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Christoph Kiehl commented on JCR-974:
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I tried building a test case, but you need a fairly large index to really see
the benefitsof my patch. In our production environment the workspace index is
500MB in size and the jcr:system index is about 1200MB (and both of course
still growing). With indexes as big as that the effect of the operation systems
file system cache is not as big as in small test cases. In my small test case
the performance with my patch was a bit worse for repeating queries on an
unchanged repository.
I think we should provide a little tool that takes the wikipedia content an
puts it all into a test repository which could then be used for such test
cases. What do you think?
> Manage Lucene FieldCaches per index segment
> -------------------------------------------
>
> Key: JCR-974
> URL: https://issues.apache.org/jira/browse/JCR-974
> Project: Jackrabbit
> Issue Type: Improvement
> Components: query
> Affects Versions: 1.3
> Reporter: Christoph Kiehl
> Attachments: ItemStateManagerBasedSortComparator.patch, patch.txt,
> patch2.txt
>
>
> Jackrabbit uses an IndexSearcher which searches on a single IndexReader which
> is most likely to be an instance of CachingMultiReader. On every search that
> does sorting or range queries a FieldCache is populated and associated with
> this instance of a CachingMultiReader. On successive queries which operate on
> this CachingMultiReader you will get a tremendous speedup for queries which
> can reuse those associated FieldCache instances.
> The problem is that Jackrabbit creates a new CachingMultiReader _everytime_
> one of the underlying indexes are modified. This means if you just change
> _one_ item in the repository you will need to rebuild all those FieldCaches
> because the existing FieldCaches are associated with the old instance of
> CachingMultiReader.
> This does not only lead to slow search response times for queries which
> contains range queries or are sorted by a field but also leads to massive
> memory consumption (depending on the size of your indexes) because there
> might be multiple instances of CachingMultiReaders in use if you have a
> scenario where a lot of queries and item modifications are executed
> concurrently.
> The goal is to keep those FieldCaches as long as possible.
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