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From "Yonik Seeley" <yo...@apache.org>
Subject Re: IndexDeletionPolicy and IndexCommitPoint
Date Sat, 07 Jun 2008 15:08:34 GMT
OK, does this mean it's now relatively safe/lightweight now to hold
references to IndexCommit objects long term (across different
IndexWriter objects on the same Directory?)

I also notice that IndexCommit.equals() only compares the segment fine
name... should it compare version also?  If index files were deleted,
and a new IndexWriter was opened, one could end up with a different
index but the same segment file name.

-Yonik

On Thu, Feb 21, 2008 at 1:25 PM, Michael McCandless
<lucene@mikemccandless.com> wrote:
> Good questions!
>
> Yes, it's best to use the segments filename to compare commit points
> across close/reopen of IndexWriter as long as you ensure you're always
> working with the same index / Directory.
>
> You could change snapshot to be a String (the segments file name) and
> do all comparisons on that basis instead of holding the
> IndexCommitPoint.  This breaks the reference to the non-static inner
> class CommitPoint in IndexFileDeleter.
>
> I like this simplification ... I've opened LUCENE-1184 for this and
> attached a patch:
>
>    https://issues.apache.org/jira/browse/LUCENE-1184
>
> Thanks Tim!
>
> Mike
>
> Tim Brennan <tim@zimbra.com> wrote:
>> When implementing a custom IndexDeletionPolicy, is it sufficient to just use the
segments filename (returned by IndexCommitPoint.getSegmentsFilename()) to compare CommitPoints
to see if they are equal?
>>
>>  I've looked at the code in SnapshotDeletionPolicy and it works by keeping a pointer
to the snapshot IndexCommitPoint and comparing that against the listed commit points in onCommit.
 This strategy doesn't seem to work if the IndexWriter is closed and re-opened: you get all
new CommitPoint instances from the new Writer even if they refer to the same logical commit,
and furthermore holding onto IndexCommitPoint references across generations of IndexWriters
will cause significant memory pressure (an IndexCommitPoint is an instance of the *non-static*
inner class IndexFileDeleter$CommitPoint so it points to the IndexFileDeleter which points
to the DocumentsWriter which points to the Posting[] array.....so holding onto a commit point
effectively keeps the Posting[] array around)
>>
>>  Am I going completely wrong here, trying to IndexDeletionPolicy across Writer generations?
>>
>>  --tim
>>
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