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From "Christoph Kiehl (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-974) Manage Lucene FieldCaches per index segment
Date Wed, 20 Jun 2007 16:54:26 GMT

    [ https://issues.apache.org/jira/browse/JCR-974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12506599

Christoph Kiehl commented on JCR-974:

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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