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https://issues.apache.org/jira/browse/LUCENE-2345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850127#action_12850127
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Tim Smith commented on LUCENE-2345:
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bq. I think we should only commit this only on 3.1 (new feature)?
3.1 only of course (just posted a 3.0 patch now as that's what i'm using and i
need the functionality now)
bq. Tim, do you think the plugin model ("extension by composition") would be
workable for your use case? Ie, instead of a factory enabling subclasses of
SegmentReader?
As long as the plugin model allows the same capabilities, that could work just
fine and could be the final solution for this ticket.
I mainly need the ability to add data structures to a SegmentReader that will
be shared for all SegmentReader's for a segment, and then add some extra meta
information on a per instance basis
Is there a ticket or wiki page that details the "plugin" architecture/design so
i could take a look?
However, would the plugins allow overriding specific IndexReader methods?
I still would see the need to be able to override specific methods for a
SegmentReader (in order to track statistics/provide
changed/different/faster/more feature rich implementations)
I don't have a direct need for this right now, however i could envision needing
this in the future
Here's a few requirements i would pose for the plugin model (maybe they are
already though of):
* Plugins have hooks to "reopen" themselves (some plugins can be shared across
all instances of a SegmentReader)
** These reopen hooks would be called during SegmentReader.reopen()
* Plugins are initialized during "SegmentReader.get/SegmentReader.reopen"
** plugins should not have to be added after the fact, as this would not allow
proper warming/initializing of plugins inside the NRT indexing
** i assume this would need be added as some list of PluginFactories added to
the IndexWriter/IndexReader.open()?
* Plugins should have a "close" method that is called in SegmentReader.close()
** This will allow proper release of any resources
* Plugins are passed an instance of the SegmentReader they are for
** Plugins should be able to access all methods on a SegmentReader
** This would effectively allow overriding a SegmentReader by having a plugin
provide the functionality instead (however only people explicitly calling the
plugin would get this benefit)
> Make it possible to subclass SegmentReader
> ------------------------------------------
>
> Key: LUCENE-2345
> URL: https://issues.apache.org/jira/browse/LUCENE-2345
> Project: Lucene - Java
> Issue Type: Wish
> Components: Index
> Reporter: Tim Smith
> Fix For: 3.1
>
> Attachments: LUCENE-2345_3.0.patch
>
>
> I would like the ability to subclass SegmentReader for numerous reasons:
> * to capture initialization/close events
> * attach custom objects to an instance of a segment reader (caches,
> statistics, so on and so forth)
> * override methods on segment reader as needed
> currently this isn't really possible
> I propose adding a SegmentReaderFactory that would allow creating custom
> subclasses of SegmentReader
> default implementation would be something like:
> {code}
> public class SegmentReaderFactory {
> public SegmentReader get(boolean readOnly) {
> return readOnly ? new ReadOnlySegmentReader() : new SegmentReader();
> }
> public SegmentReader reopen(SegmentReader reader, boolean readOnly) {
> return newSegmentReader(readOnly);
> }
> }
> {code}
> It would then be made possible to pass a SegmentReaderFactory to IndexWriter
> (for pooled readers) as well as to SegmentReader.get() (DirectoryReader.open,
> etc)
> I could prepare a patch if others think this has merit
> Obviously, this API would be "experimental/advanced/will change in future"
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