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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2345) Make it possible to subclass SegmentReader
Date Fri, 26 Mar 2010 11:10:27 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850082#action_12850082
] 

Michael McCandless commented on LUCENE-2345:
--------------------------------------------

OK, I guess for now let's hold off on this issue while we iterate at least with Earwin's first
refactoring effort...?

Earwin, can you post a patch w/ your current state, even if it's "rough"?  There seems to
be alot of interest/opinions on how to "fix" things here :)  Both IndexWriter & SegmentReader
are "needing" extensibility... but this is a big change so I'm hoping we can first just get
your refactoring done before adding extensibility.

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?

> 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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