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https://issues.apache.org/jira/browse/LUCENE-2402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12858738#action_12858738
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Michael McCandless commented on LUCENE-2402:
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bq. Lets reuse IW.deleteUnusedFiles() ?
+1
> Add an explicit method to invoke IndexDeletionPolicy
> ----------------------------------------------------
>
> Key: LUCENE-2402
> URL: https://issues.apache.org/jira/browse/LUCENE-2402
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Shai Erera
> Assignee: Shai Erera
> Fix For: 3.1
>
>
> Today, if one uses an IDP which holds onto segments, such as
> SnapshotDeletionPolicy, or any other IDP in the tests, those segments are
> left in the index even if the IDP no longer references them, until
> IW.commit() is called (and actually does something). I'd like to add a
> specific method to IW which will invoke the IDP's logic and get rid of the
> unused segments w/o forcing the user to call IW.commit(). There are a couple
> of reasons for that:
> * Segments take up sometimes valuable HD space, and the application may wish
> to reclaim that space immediately. In some scenarios, the index is updated
> once in several hours (or even days), and waiting until then may not be
> acceptable.
> * I think it's a cleaner solution than waiting for the next commit() to
> happen. One can still wait for it if one wants, but otherwise it will give
> you the ability to immediately get rid of those segments.
> * TestSnapshotDeletionPolicy includes this code, which only strengthens (IMO)
> the need for such method:
> {code}
> // Add one more document to force writer to commit a
> // final segment, so deletion policy has a chance to
> // delete again:
> Document doc = new Document();
> doc.add(new Field("content", "aaa", Field.Store.YES, Field.Index.ANALYZED,
> Field.TermVector.WITH_POSITIONS_OFFSETS));
> writer.addDocument(doc);
> {code}
> If IW had an explicit method, that code would not need to exist there at all
> ...
> Here comes the fun part - naming the baby:
> * invokeDeletionPolicy -- describes exactly what is going to happen. However,
> if the user did not set IDP at all (relying on default, which I think many
> do), users won't understand what is it.
> * deleteUnusedSegments - more user-friendly, assuming users understand what
> 'segments' are.
> BTW, IW already has deleteUnusedFiles() which only tries to delete
> unreferenced files that failed to delete before (such as on Windows, due to
> e.g. open readers). Perhaps instead of inventing a new name, we can change
> IW.deleteUnusedFiles to call IndexFileDeleter.checkpoint (instead of
> deletePendingFiles) which deletes those files + calls IDP.onCommit().
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