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From Otis Gospodnetic <otis_gospodne...@yahoo.com>
Subject Re: Why Lucene takes longer time for the first query and less for subsequent ones
Date Tue, 17 Nov 2009 19:37:44 GMT
Hello,

Most likely due to the operating system caching the relevant portions of the index after the
first set of queries.

Otis
--
Sematext is hiring -- http://sematext.com/about/jobs.html?mls
Lucene, Solr, Nutch, Katta, Hadoop, HBase, UIMA, NLP, NER, IR



----- Original Message ----
> From: Dinh <pcdinh@gmail.com>
> To: java-user@lucene.apache.org
> Sent: Tue, November 17, 2009 12:39:14 PM
> Subject: Why Lucene takes longer time for the first query and less for  subsequent ones
> 
> Hi all,
> 
> I made a list of 4 simple, singe term queries and do 4 searches via Lucene
> and find that if the term is used for search in the first time, Lucene takes
> quite a bit time to handle it.
> 
> - Query A
> 00:27:28,781  INFO LuceneSearchService:151 - Internal search took
> 328.21463ms
> 00:27:28,781  INFO SearchController:86 - Page rendered in 338.29553ms
> 
> - Query B
> 00:27:39,171  INFO LuceneSearchService:151 - Internal search took
> 480.30908ms
> 00:27:39,187  INFO SearchController:86 - Page rendered in 493.07327ms
> 
> - Query C
> 00:27:46,765  INFO LuceneSearchService:151 - Internal search took
> 189.33635ms
> 00:27:46,765  INFO SearchController:86 - Page rendered in 195.43823ms
> 
> - Query D
> 00:28:00,312  INFO LuceneSearchService:151 - Internal search took 330.3596ms
> 00:28:00,328  INFO SearchController:86 - Page rendered in 347.34747ms
> 
> 
> It looks no good at the first glance because I have only 500 000 indexed
> documents. However, when I searched them again I found that Lucene run much
> faster.
> 
> - Query A
> 00:28:04,046  INFO LuceneSearchService:151 - Internal search took 3.90301ms
> 00:28:04,062  INFO SearchController:86 - Page rendered in 15.694173ms
> 
> - Query C
> 00:28:15,390  INFO LuceneSearchService:151 - Internal search took 1.425879ms
> 00:28:15,390  INFO SearchController:86 - Page rendered in 7.946541ms
> 
> - Query D
> 00:28:26,031  INFO LuceneSearchService:151 - Internal search took 1.849956ms
> 00:28:26,046  INFO SearchController:86 - Page rendered in 12.023037ms
> 
> - Query B
> 00:28:31,609  INFO LuceneSearchService:151 - Internal search took 1.668648ms
> 00:28:31,625  INFO SearchController:86 - Page rendered in 15.57237ms
> 
> Why does it happens? Does it mean that Lucene has an internal cache engine,
> just like MySQL query result cache or Oracle query execution plan cache?
> 
> Thanks
> 
> Dinh


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