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Re: What's the best hardver for PostgreSQL 8.1?

From: William Yu <wyu(at)talisys(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: What's the best hardver for PostgreSQL 8.1?
Date: 2005-12-24 22:36:57
Message-ID: dokii5$2bba$1@news.hub.org (view raw or flat)
Thread:
Lists: pgsql-performance
David Lang wrote:
> raid 5 is bad for random writes as you state, but how does it do for 
> sequential writes (for example data mining where you do a large import 
> at one time, but seldom do other updates). I'm assuming a controller 
> with a reasonable amount of battery-backed cache.

Random write performance (small block that only writes to 1 drive):
1 write requires N-1 reads + N writes --> 1/2N-1 %

Sequential write performance (write big enough block to use all N drives):
N-1 Write requires N writes --> N-1/N %

Assuming enough cache so all reads/writes are done in 1 transaction + 
onboard processor calcs RAID parity fast enough to not cause an extra delay.

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