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From Doug Cutting <cutt...@lucene.com>
Subject Re: suggestion for a CustomDirectory
Date Fri, 05 Dec 2003 18:12:56 GMT
Julien Nioche wrote:
> Profiling my application indicates that a lot of times is spent for the
> creation of temporary Term objects.

It does indeed look like term lookup is using a lot of your time.  I 
don't see the Term constructor showing up as significant in your 
profile, so it looks to me like it could just the cost of parsing the 
data, not the allocation/GC stuff.  I've found that allocation of 
temporary objects doesn't really cost much with modern garbage 
collectors.  The biggest cost of allocating objects is sometimes just 
the constructor.

What sort of queries are you making against what sort of an index?  It 
looks like you're probably making large queries with lots of 
low-frequency terms, in order for term lookup to be such a large factor. 
  You might try sorting the terms in the query.  If subsequent lookups 
are nearby in the TermInfo file then it won't have to scan as much. 
Could that help?  Also, is your index optimized?  An optimized index 
will drastically reduce the term lookup costs.

If all these fail, try reducing TermInfosWriter.INDEX_INTERVAL.  You'll 
have to re-create your indexes each time you change this constant.  You 
might try a value like 16.  This would keep the number of terms in 
memory from being too huge (1 of 16 terms), but would reduce the average 
number scanned from 64 to 8, which would be substantial.  Tell me how 
this works.  If it makes a big difference, then perhaps we should make 
this parameter more easily changable.

Doug


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