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Variation between query runtimes 2+ messages / 2 participants [nested] [flat]
* Variation between query runtimes @ 2006-06-11 06:35 John Top-k apad <topkapad@gmail.com> 2006-06-12 02:50 ` Re: Variation between query runtimes Qingqing Zhou <zhouqq@cs.toronto.edu> 0 siblings, 1 reply; 2+ messages in thread From: John Top-k apad @ 2006-06-11 06:35 UTC (permalink / raw) To: pgsql-performance Hi, I have the following quering plans: "Seq Scan on ind_uni_100 (cost=0.00..27242.00 rows=1000000 width=104) (actual time=0.272..2444.667 rows=1000000 loops=1)" "Total runtime: 4229.449 ms" and "Bitmap Heap Scan on ind_uni_100 (cost=314.00..18181.00 rows=50000 width=104) (actual time=74.106..585.368 rows=49758 loops=1)" " Recheck Cond: (b = 1)" " -> Bitmap Index Scan on index_b_ind_uni_100 (cost=0.00..314.00rows=50000 width=0) (actual time= 61.814..61.814 rows=49758 loops=1)" " Index Cond: (b = 1)" "Total runtime: 638.787 ms" from pg_stast_get_blocks_fetched i can see that both queries need almost the same number of disk fetches which is quite reasonable ( the index is unclustered). But as you can see there is a great variation between query runtimes.Cansomeone explain this differnce? Thanks! ^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Variation between query runtimes 2006-06-11 06:35 Variation between query runtimes John Top-k apad <topkapad@gmail.com> @ 2006-06-12 02:50 ` Qingqing Zhou <zhouqq@cs.toronto.edu> 0 siblings, 0 replies; 2+ messages in thread From: Qingqing Zhou @ 2006-06-12 02:50 UTC (permalink / raw) To: pgsql-performance ""John Top-k apad"" <topkapad@gmail.com> wrote > > from pg_stast_get_blocks_fetched i can see that both queries need almost the > same number of disk fetches which is quite reasonable ( the index is > unclustered). > > But as you can see there is a great variation between query > runtimes.Cansomeone explain this differnce? > Can you give a self-contained example (including what you did to clear the file system cache (maybe unmount?) to *not* let the 2nd query to use the file content from the 1st query)? Regards, Qingqing ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2006-06-12 02:50 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2006-06-11 06:35 Variation between query runtimes John Top-k apad <topkapad@gmail.com> 2006-06-12 02:50 ` Qingqing Zhou <zhouqq@cs.toronto.edu>
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