Re: weird performances problem

"Guillaume Smet" <guillaume(dot)smet(at)openwide(dot)fr> wrote
> [root(at)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