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From "Nick Bailey" <nicholas.bai...@rackspace.com>
Subject IndexReader.isCurrent for cached indexes
Date Wed, 09 Sep 2009 21:33:24 GMT
Looking for some help figuring out a problem with the IndexReader.isCurrent() method and cached
indexes.  

We have a number of lucene indexes that we attempt to keep in memory after an initial query
is performed.  In order to prevent the indexes from becoming stale, we check for changes
about every minute by calling isCurrent().  If the index has changed, we will then reopen
it.

From our logs it appears that in some cases isCurrent() will return true even though the index
has changed since the last time the reader was opened.  

The code to refresh the index is basically this:

// Checked every minute
if(!reader.isCurrent()){
  // reopen the existing reader
  reader = this.searcher.getIndexReader();
  reader = reader.reopen();
}

This is an example of the problem from the logs:

2009-08-29 17:50:51,387 Indexed 0 documents and deleted 1 documents from index 'example' in
0 ms
2009-08-30 03:11:58,410 Indexed 0 documents and deleted 5 documents from index 'example' in
0 ms
2009-08-30 16:30:03,466 Using cached reader <age=88648201 lastRefresh=81415526> 
// numbers indicate milliseconds since opened or refreshed aka age = 24.6hrs, lastRefresh
= 22.6hrs

The logs indicate we deleted documents from the index at about 5:50 on August 29th, and then
again on the 30th at 3:11.  Then at 4:30 on we attempted to query the index.  We found the
cached reader and used it, however, the last time the cache was refreshed was about 22 hours
previously, coinciding with the first delete.  The index should have been reopened after
the second delete.

I have checked, and the code to refresh the indexes is definitely being run every 60 seconds.
 All I can see is that the problem might be with the isCurrent() method.  

Could it be due to holding the reader open for so long? Any other ideas?

Thanks a lot,
Nick Bailey



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