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https://issues.apache.org/jira/browse/LUCENE-743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12536044
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Michael Busch commented on LUCENE-743:
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{quote}
The implementation seems simple. When a reader is opened, it starts with RC 1.
When it is closed, it decrefs the RC and marks itself closed (to make sure
double-close does not re-decref the RC). When a MultiReader needs to use the
reader, it calls incref. And when that MultiReader is done with it, it calls
decref. Whenever the RC hits 0 it's safe to free all resources.
Wouldn't that work?
{quote}
You're right, for a MultiReader and ParallelReader this would work and wouldn't
be hard to implement.
It is quite different when it comes to SegmentReaders. SegmentReader.reopen()
checks SegmentInfos if there is a segment with the same name but newer normGen
or delGen. If there is one then a new SegmentReader instance is created that
reuses resources like e. g. TermInfosReader and loads the new generation of the
del or norm file.
Now you can end up having a bunch of SegmentReaders that share the same
resources but don't know about each other. The reference counting would have to
happen somewhere else, e. g. in the TermInfosReader. Of course this is doable,
but it's a special case and more complicated compared to the "restrict reopen()
to only be called once"-approach.
> IndexReader.reopen()
> --------------------
>
> Key: LUCENE-743
> URL: https://issues.apache.org/jira/browse/LUCENE-743
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Otis Gospodnetic
> Assignee: Michael Busch
> Priority: Minor
> Fix For: 2.3
>
> Attachments: IndexReaderUtils.java, lucene-743-take2.patch,
> lucene-743.patch, lucene-743.patch, lucene-743.patch, MyMultiReader.java,
> MySegmentReader.java, varient-no-isCloneSupported.BROKEN.patch
>
>
> This is Robert Engels' implementation of IndexReader.reopen() functionality,
> as a set of 3 new classes (this was easier for him to implement, but should
> probably be folded into the core, if this looks good).
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