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https://issues.apache.org/jira/browse/LUCENE-1749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12732110#action_12732110
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Hoss Man commented on LUCENE-1749:
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The motivation for this issue is all of the changes coming in 2.9 in how Lucene
internally uses the FieldCache API -- the biggest change being per Segment
sorting, but there may be others not immediately obvious.
While these changes are backwards compatible from an API and functionality
perspective, they could have some pretty serious performance impacts for
existing apps that also use the FieldCache directly and after upgrading the
apps suddenly seem slower to start (because of redundant FieldCache
initialization) and require 2X as much RAM as they did before. This could lead
people people to assume Lucene has suddenly became a major memory hog.
SOLR-1111 and SOLR-1247 are some quick examples of the types of problems that
apps could encounter.
Currently the only way for a User to even notice the problem is to do memory
profiling, and the FieldCache data structure isn't the easiest to understand.
It would be a lot nicer to have some methods for doing this inspection
programaticly, so users could write automated tests for incorrect/redundent
usage.
> FieldCache introspection API
> ----------------------------
>
> Key: LUCENE-1749
> URL: https://issues.apache.org/jira/browse/LUCENE-1749
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Hoss Man
> Priority: Minor
>
> FieldCache should expose an Expert level API for runtime introspection of the
> FieldCache to provide info about what is in the FieldCache at any given
> moment. We should also provide utility methods for sanity checking that the
> FieldCache doesn't contain anything "odd"...
> * entries for the same reader/field with different types/parsers
> * entries for the same field/type/parser in a reader and it's subreader(s)
> * etc...
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