Message-ID: <50BE2533.5050101@kickstone.com>
Date: Tue, 04 Dec 2012 16:30:43 +0000
From: John Lister <john.lister@kickstone.com>
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To: Merlin Moncure <mmoncure@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Comparative tps question
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On 29/11/2012 17:33, Merlin Moncure wrote:
> one thing that immediately jumps out here is that your wal volume 
> could be holding you up. so it's possible we may want to move wal to 
> the ssd volume. if you can scrounge up a 9.2 pgbench, we can gather 
> more evidence for that by running pgbench with the "--unlogged-tables" 
> option, which creates the tables unlogged so that they are not wal 
> logged (for the record, this causes tables to be truncated when not 
> shut down in clean state).
Ok, got myself a 9.2 version of pgbench and run it a few times on 
unlogged tables...
changing the number of threads has maybe a 5% change in values which 
isn't probably too much to worry about.
-j 25 -c 100 -s 100 gives a tps of around 10.5k
using -N ups that to around 20k
using -S ups that again to around 40k

I'll have to wait until I get to shut the db down again to try the wal 
on an ssd. Although unless I did something wrong it didn't seem to make 
a huge difference before....

During these tests, iowait dropped to almost 0, user and sys stayed 
around the same (60% and 20% respectively). although the disk traffic 
was only in the 10s of Mb/s which seems very low - unless there is some 
wierd caching going on and it gets dumped at a later date?


John

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