| From: | Jesper Krogh <jesper(at)krogh(dot)cc> |
|---|---|
| To: | Scott Carey <scott(at)richrelevance(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>, "david(at)lang(dot)hm" <david(at)lang(dot)hm>, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Vitalii Tymchyshyn <tivv00(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Slow count(*) again... |
| Date: | 2010-10-21 18:13:24 |
| Message-ID: | 4CC082C4.4070704@krogh.cc |
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| Lists: | pgsql-hackers pgsql-performance |
On 2010-10-21 06:47, Scott Carey wrote:
> On a wimpy disk, I/O bound for sure. But my disks go 1000MB/sec.
> No query can go fast enough for them. The best I've gotten is
> 800MB/sec, on a wide row (average 800 bytes). Most tables go
> 300MB/sec or so. And with 72GB of RAM, many scans are in-memory
> anyway.
Is it cpu or io bound while doing it?
Can you scan it faster using time cat relation-oid.* > /dev/null
> A single SSD with supercapacitor will go about 500MB/sec by itself
> next spring. I will easily be able to build a system with 2GB/sec
> I/O for under $10k.
What filesystem are you using? Readahead?
Can you try to check the filesystemfragmentation of the table using filefrag?
--
Jesper
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