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https://issues.apache.org/jira/browse/JCR-974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12506499
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Marcel Reutegger commented on JCR-974:
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btw, both SearchIndex.CombinedIndexReader and CachingMultiReader implement
MultiIndexReader which exposes getIndexReaders().
> 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
>
>
> 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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