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From Mark Kristensson <>
Subject Re: IndexWriter.close() performance issue
Date Wed, 03 Nov 2010 23:37:15 GMT
Yes, we do have a large number of unique field names in that index, because they are driven
by user named fields in our application (with some cleaning to remove illegal chars).

This slowness problem has appeared very suddenly in the last couple of weeks and the number
of unique field names has not spiked in the last few weeks. Have we crept over some threshold
with our linear growth in the number of unique field names? Perhaps there is a limit driven
by the amount of RAM in the machine that we are violating? Are there any guidelines for the
maximum number, or suggested number, of unique fields names in an index or segment? Any suggestions
for potentially mitigating the problem? 


On Nov 3, 2010, at 2:02 PM, Michael McCandless wrote:

> On Wed, Nov 3, 2010 at 4:27 PM, Mark Kristensson
> <> wrote:
>> I've run checkIndex against the index and the results are below. That net is that
it's telling me nothing is wrong with the index.
> Thanks.
>> I did not have any instrumentation around the opening of the IndexSearcher (we don't
use an IndexReader), just around the actual query execution so I had to add some additional
logging. What I found surprised me, opening a search against this index takes the same 6 to
8 seconds that closing the indexWriter takes.
> IndexWriter opens a SegmentReader for each segment in the index, to
> apply deletions, so I think this is the source of the slowness.
> From the CheckIndex output, it looks like you have many (296,713)
> unique fields names on that one large segment -- does that sound
> right?  I suspect such a very high field count is the source of the
> slowness...
> Mike
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