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https://issues.apache.org/jira/browse/LUCENE-831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12582443#action_12582443
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Michael Busch commented on LUCENE-831:
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{quote}
The benefit then is that reopen() of a reader would not have to
allocate & bulk copy massive arrays when updating the caches. It
would keep the cost of reopen closer to the size of the new segments.
{quote}
I agree, Mike. Currently during reopen() the MultiSegmentReader
allocates a new norms array with size maxDoc(), which is, as you said,
inefficient if only some (maybe even small) segments changed.
The method call might be a little slower than the array lookup, but
I doubt that this would be very significant. We can make this change for
the norms and run performance tests to measure the slowdown.
> Complete overhaul of FieldCache API/Implementation
> --------------------------------------------------
>
> Key: LUCENE-831
> URL: https://issues.apache.org/jira/browse/LUCENE-831
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Hoss Man
> Assignee: Michael Busch
> Fix For: 2.4
>
> Attachments: fieldcache-overhaul.032208.diff,
> fieldcache-overhaul.diff, fieldcache-overhaul.diff
>
>
> Motivation:
> 1) Complete overhaul the API/implementation of "FieldCache" type things...
> a) eliminate global static map keyed on IndexReader (thus
> eliminating synch block between completley independent IndexReaders)
> b) allow more customization of cache management (ie: use
> expiration/replacement strategies, disk backed caches, etc)
> c) allow people to define custom cache data logic (ie: custom
> parsers, complex datatypes, etc... anything tied to a reader)
> d) allow people to inspect what's in a cache (list of CacheKeys) for
> an IndexReader so a new IndexReader can be likewise warmed.
> e) Lend support for smarter cache management if/when
> IndexReader.reopen is added (merging of cached data from subReaders).
> 2) Provide backwards compatibility to support existing FieldCache API with
> the new implementation, so there is no redundent caching as client code
> migrades to new API.
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