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From: Qingqing Zhou <zhouqq@cs.toronto.edu>
To: pgsql-performance@postgresql.org
Subject: Re: weird performances problem
Date: Tue, 22 Nov 2005 02:21:12 -0500
Message-ID: <dlugsf$25o5$1@news.hub.org> (raw)
References: <437CC21D.8070402@openwide.fr>


"Guillaume Smet" <guillaume.smet@openwide.fr> wrote
> [root@bd root]# iostat 10
>
> Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
> sda               7.20         0.00        92.00          0        920
> sda1              0.00         0.00         0.00          0          0
> sda2              6.40         0.00        78.40          0        784
> sda3              0.00         0.00         0.00          0          0
> sda4              0.00         0.00         0.00          0          0
> sda5              0.00         0.00         0.00          0          0
> sda6              0.80         0.00        13.60          0        136
> sdb               5.00         0.00       165.60          0       1656
> sdb1              5.00         0.00       165.60          0       1656
>
> Nested Loop  (cost=0.00..13.52 rows=2 width=1119) (actual 
> time=155.286..155.305 rows=1 loops=1)
>   ->  Index Scan using pk_newslang on newslang nl  (cost=0.00..3.87 rows=1 
> width=1004) (actual time=44.575..44.579 rows=1 loops=1)
>         Index Cond: (((codelang)::text = 'FRA'::text) AND (3498704 = 
> numnews))
>   ->  Nested Loop Left Join  (cost=0.00..9.61 rows=2 width=119) (actual 
> time=110.648..110.660 rows=1 loops=1)
>         ->  Index Scan using pk_news on news n  (cost=0.00..3.31 rows=2 
> width=98) (actual time=0.169..0.174 rows=1 loops=1)
>               Index Cond: (numnews = 3498704)
>         ->  Index Scan using pk_photo on photo p  (cost=0.00..3.14 rows=1 
> width=25) (actual time=110.451..110.454 rows=1 loops=1)
>               Index Cond: (p.numphoto = "outer".numphoto)
> Total runtime: 155.514 ms
>

Someone is doing a massive *write* at this time, which makes your query 
*read* quite slow. Can you find out which process is doing write?

Regards,
Qingqing 





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