From: Tomas Vondra <tv@fuzzy.cz>
To: pgsql-performance@postgresql.org
Subject: Re: Two identical systems, radically different performance
Date: Tue, 09 Oct 2012 01:24:02 +0200
Message-ID: <50736092.8080906@fuzzy.cz> (raw)
In-Reply-To: <B5EA62D3-A446-4A1F-BC4E-4B8290FEE1C2@gmail.com>
References: <CAFwQ8rcvw4mSoJ9q+ouONCeB9dg1T9gAUV5J27MpVZrehRHayQ@mail.gmail.com>
<B5EA62D3-A446-4A1F-BC4E-4B8290FEE1C2@gmail.com>
On 9.10.2012 00:33, Evgeny Shishkin wrote:
>>
>> pgbench: Old server
>>
>> pgbench -i -s 100 -U test
>> pgbench -U test -c ... -t ...
>>
>> -c -t TPS
>> 5 20000 3777
>> 10 10000 2622
>> 20 5000 3759
>> 30 3333 5712
>> 40 2500 5953
>> 50 2000 6141
>>
>> New server
>> -c -t TPS
>> 5 20000 2733
>> 10 10000 2783
>> 20 5000 3241
>> 30 3333 2987
>> 40 2500 2739
>> 50 2000 2119
>
> On new server postgresql do not scale at all. Looks like contention.
Why? The evidence we've seen so far IMHO suggests a poorly performing
I/O subsystem. Post a few lines of "vmstat 1" / "iostat -x -k 1"
collected when the pgbench is running, that might tell us more.
Try a few very basic I/O tests that are easy to understand rather than
running bonnie++ which is quite complex. For example try this:
time sh -c "dd if=/dev/zero of=myfile.tmp bs=8192 count=4194304 && sync"
dd if=myfile.tmp of=/dev/null bs=8192
The former measures sequential write speed, the latter measures
sequential read speed in a very primitive way. Watch vmstat/iostat and
don't bother running pgbench until you get a reasonable performance on
both systems.
Tomas
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Subject: Re: Two identical systems, radically different performance
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