From: Piotr Legiecki <piotrlg@ams.edu.pl>
To: Scott Marlowe <scott.marlowe@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: old server, new server, same performance
Date: Mon, 17 May 2010 11:52:17 +0200
Message-ID: <4BF111D1.2000101@ams.edu.pl> (raw)
In-Reply-To: <AANLkTim_flRDNYlOsr3owClWvb0pRVCD_R5Xpx8r780A@mail.gmail.com>
References: <4BED08B4.4030507@sci.pam.szczecin.pl>
<AANLkTimf8KfFVGL5E3aVwGutNT1kveJmD4nsc2HtLnbn@mail.gmail.com>
<4BF0F8FF.5040703@ams.edu.pl>
<AANLkTilnF7pHezPdQjvoKq8slPr34uG_ZoSTv1ntKxi_@mail.gmail.com>
<AANLkTim_flRDNYlOsr3owClWvb0pRVCD_R5Xpx8r780A@mail.gmail.com>
Scott Marlowe pisze:
>>> So still I don't get this: select * from table; on old server takes 0,5 sec,
>>> on new one takes 6sec. Why there is so big difference? And it does not
>>> matter how good or bad select is to measure performance, because I don't
>>> measure the performance, I measure the relative difference. Somwhere there
>>> is a bottleneck.
>> Yep, the network I'd say. How fast are things like scp between the
>> various machines?
Sure it is, but not in a way one could expect:
- scp from 1000Gbit laptop to old server 27MB/sec
- scp from the same laptop to new server 70MB/sec
Both servers have 1000Gbit connection. So it is still mysterious why old
server makes 9x faster select?
I don't claim that something is slow on new (or even older) server. Not
at all. the application works fine (still on older machine). I only
wonder about those differences.
>>> 4. Machine. The new server has 5 SAS disks (+ 1 spare), but I don't remember
>>> how they are set up now (looks like mirror for system '/' and RAID5 for rest
>>> - including DB). size of the DB is 405MB
>> Get off of RAID-5 if possible. A 3 Disk RAID-5 is the slowest
>> possible combination for RAID-5 and RAID-5 is generally the poorest
>> choice for a db server.
Sure I know that RAID-5 is slower than mirror but anyway how much
slower? And for sure not as much as single ATA disk.
> I refer you to this classic post on the subject:
> http://www.mail-archive.com/pgsql-general@postgresql.org/msg93043.html
Well, this thread is about benchmarking databases (or even worse,
comparison between two RDBMS). I'm not benchmarking anything, just
compare one factor.
P.
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To: pgsql-performance@postgresql.org
Cc: piotrlg@ams.edu.pl, scott.marlowe@gmail.com
Subject: Re: old server, new server, same performance
In-Reply-To: <4BF111D1.2000101@ams.edu.pl>
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