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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1703) Add a waitForMerges() method to IndexWriter
Date Fri, 19 Jun 2009 19:28:07 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1703?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12721951#action_12721951
] 

Shai Erera commented on LUCENE-1703:
------------------------------------

May I ask what's the use case for this? I looked at IndexWriter and the following have doWait
versions: close(), optimize() and expungeDeletes(). The only one that doesn't is commit(),
which documents it will not wait for merges. So this seems to be a method just for

{code}
try { 
  writer.commit(); 
} finally { 
  writer.waitForMerges(); 
}
{code}

Is there any other use case that you would want to wait for merges to finish?

It's just that adding methods means we need to support them going forward, and if there's
no real use case (or at least none that is covered by current API), we should not do it?

> Add a waitForMerges() method to IndexWriter
> -------------------------------------------
>
>                 Key: LUCENE-1703
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1703
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.4
>            Reporter: Tim Smith
>         Attachments: IndexWriter.java.diff
>
>
> It would be very useful to have a waitForMerges() method on the IndexWriter.
> Right now, the only way i can see to achieve this is to call IndexWriter.close()
> ideally, there would be a method on the IndexWriter to wait for merges without actually
closing the index.
> This would make it so that background merges (or optimize) can be waited for without
closing the IndexWriter, and then reopening a new IndexWriter
> the close() reopen IndexWriter method can be problematic if the close() fails as the
write lock won't be released
> this could then result in the following sequence:
> * close() - fails
> * force unlock the write lock (per close() documentation)
> * new IndexWriter() (acquires write lock)
> * finalize() on old IndexWriter releases the write lock
> * Index is now not locked, and another IndexWriter pointing to the same directory could
be opened
> If you don't force unlock the write lock, opening a new IndexWriter will fail until garbage
collection calls finalize() the old IndexWriter
> If the waitForMerges() method is available, i would likely never need to close() the
IndexWriter until right before the process being shutdown, so this issue would not occur (worst
case scenario, the waitForMerges() fails)

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