From: William Yu <wyu@talisys.com>
To: pgsql-performance@postgresql.org
Subject: Re: What's the best hardver for PostgreSQL 8.1?
Date: Sat, 24 Dec 2005 14:36:57 -0800
Message-ID: <dokii5$2bba$1@news.hub.org> (raw)
In-Reply-To: <Pine.LNX.4.62.0512241350010.2807@qnivq.ynat.uz>
References: <43A84D03.7090002@ritek.hu>
<docq5v$24ea$1@news.hub.org>
<200512212209.50234.caseroj@comcast.net>
<200512212231.55100.caseroj@comcast.net>
<20051224135042.484c6e32.frank@wiles.org>
<6.2.5.6.0.20051224161551.01dc5d98@earthlink.net>
<Pine.LNX.4.62.0512241350010.2807@qnivq.ynat.uz>
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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To: pgsql-performance@postgresql.org
Cc: wyu@talisys.com
Subject: Re: What's the best hardver for PostgreSQL 8.1?
In-Reply-To: <dokii5$2bba$1@news.hub.org>
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