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From "Luc Vanlerberghe (JIRA)" <>
Subject [jira] Created: (LUCENE-485) IndexWriter.mergeSegments should not hold the commit lock while cleaning up.
Date Mon, 09 Jan 2006 19:11:21 GMT
IndexWriter.mergeSegments should not hold the commit lock while cleaning up.

         Key: LUCENE-485
     Project: Lucene - Java
        Type: Improvement
  Components: Index  
    Versions: CVS Nightly - Specify date in submission    
 Environment: checked in revision 367361
    Reporter: Luc Vanlerberghe

Same happens in IndexWriter.addIndexes(IndexReader[] readers).

The commit lock should be obtained whenever the Index structure/version is read or written.
 It should be kept for as short a period as possible.

The write lock is needed to make sure only one IndexWriter or IndexReader instance can update
the index (multiple IndexReaders can of course use the index for searching).

The list of files that can be deleted is stored in the file "deletable".  It is only read
or written by the IndexWriter instance that holds the write lock, so there's no need to have
the commit lock to to update it.

On my production system deleting the obsolete segment files after a mergeSegments() happens
can occasionally take several seconds(!) and the commit lock blocks the searcher machines
from updating their IndexReader instance.
Even on a standalone machine, the time to update the segments file is about 3ms, the time
to delete the obsolete segments about 30ms.

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