From: | "Scott Buchan" <sbuchan(at)technicacorp(dot)com> |
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To: | <pgsql-performance(at)postgresql(dot)org> |
Subject: | Large difference between elapsed time and run time for queries |
Date: | 2003-03-10 18:58:26 |
Message-ID: | 71F044551C53974EB0735B3737EFE2FC088628@wwwserver |
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Lists: | pgsql-performance |
Hello,
While running benchmarks for my database, I am seeing a large difference in
the elapsed time (from stats collected in the logs) and run time (running
explain analyze on the query using ./psql <database>) for each of my
queries. The database is being ran on a sunfire 880 with 4 750mhz
processors with 8 G RAM running solaris 8
I am simulating 200 user connections each running 6 select queries on 1
indexed table with 50,000 records. The elapsed time for the queries average
around 2.5 seconds while if I run the query using explain analyze while the
test is running, the run time is around 300 ms although it takes much longer
(few seconds) to display the results. If I reduce the number of concurrent
connections to 100 then the run time and elapsed time for the queries are
the same.
I have tried numerous configurations in the postgresql.conf file. I have
set the shared_buffers with values ranging from 75 MB to 4000MB with no
luck. I have also tried increasing the sort_mem with no luck.
When the test is running, the cpu is well over 50% idle and iostat shows
that the processes are not waiting for i/o and disk usage percentage is low.
Any help would be appreciated.
Thanks.
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