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Re: Database size Vs performance degradation

From: Matthew Wakeling <matthew(at)flymine(dot)org>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Database size Vs performance degradation
Date: 2008-07-30 12:36:42
Message-ID: Pine.LNX.4.64.0807301331550.4250@aragorn.flymine.org (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, 30 Jul 2008, Dave North wrote:
> Running on HP DL380 w/ 4GB RAM, dual 10K HDDs in RAID 0+1

> Checking the stats, the DB size is around 7.5GB;

Doesn't fit in RAM.

> ...after the load, the DB size was around 2.7GB

Does fit in RAM.

> One observation I've made on the DB system is the disk I/O seems
> dreadfully slow...we're at around 75% I/O wait sometimes and the read
> rates seem quite slow (hdparm says around 2.2MB/sec - 20MB/sec for
> un-cached reads).

That's incredibly slow in this day and age, especially from 10krpm HDDs. 
Definitely worth investigating.

However, I think vacuuming more agressively is going to be your best win 
at the moment.

Matthew

-- 
Patron: "I am looking for a globe of the earth."
Librarian: "We have a table-top model over here."
Patron: "No, that's not good enough. Don't you have a life-size?"
Librarian: (pause) "Yes, but it's in use right now."

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