[jira] Updated: (LUCENE-2402) Add an explicit method to invoke IndexDeletionPolicy

["Shai Erera (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-2402?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Shai Erera updated LUCENE-2402:
-------------------------------

    Attachment: LUCENE-2402.patch

Patch changes deleteUnusedFiles to call IFD.checkpoint and also adds a testDeleteUnusedFiles2 to TestIndexWriter.

Currently, TestIndexWriterReader.testDuringAddIndexes fails, if deleteUnusedFiles is coded like this:
{code}
public synchronized void deleteUnusedFiles() throws IOException {
  deleter.checkpoint(segmentInfos, true);
}
{code}

The failure happens in CommitPoint's ctor in the assert statement which verifies the SegmentInos does not have external Directory. When I debug-traced the test, it passed and so I concluded it's a concurrency issue (and indeed testDuringAddIndexes spawns several threads.

addIndexesNoOptimize does change SegmentInfos as it adds indexes, however at the end it 'fixes' their Directory reference. I wondered how is regular commit() works when addIndexesNoOptimize is called, but couldn't find any synchronization block where one blocks the other. Eventually, I've changed deleteUnusedFiles to this:
{code}
public synchronized void deleteUnusedFiles() throws IOException {
  synchronized (commitLock) {
    deleter.checkpoint(rollbackSegmentInfos, true);
    // deleter.checkpoint((SegmentInfos) segmentInfos.clone(), true);
  }
}
{code}

I've tried to sync on commitLock (which seems good anyway), but the test kept failing. Even cloning SI did not work because it might have changed just before the clone. Only when passing rollbackSI to checkpoint does the test pass. But I'm not sure if that's the right solution, as when I debug-traced it and put a break point just before the call to checkpoint, SI included one segment w/ a different name than rollbackSI ...

BTW, the test fails on DirReader.doClose, where it checks if writer != null and then calls deleteUnusedFiles. So I guess it's a NRT problem only.

In general, that that addIndexesNoOptimize messes w/ SI seems dangerous to me, because that's undocumented and unprotected - e.g. if someone extends IW and adds some logic which requires reading SI ... I'm not sure how to solve it, but that seems unrelated to that issue (probably much more complicated to solve).

> 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
>
>         Attachments: LUCENE-2402.patch
>
>
> 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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