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Re: IDE x SAS RAID 0 on HP DL 380 G5 P400i controller performance problem

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Daniel Ferreira de Lima" <dfl(dot)man(at)gmail(dot)com>, <pgsql-performance(at)postgresql(dot)org>
Subject: Re: IDE x SAS RAID 0 on HP DL 380 G5 P400i controller performance problem
Date: 2010-07-19 13:28:03
Message-ID: 4C440C93020000250003388D@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-performance
Daniel Ferreira de Lima <dfl(dot)man(at)gmail(dot)com> wrote:
 
> **Both with Linux Kernel 2 .4.37.9 and Postgresql 7.2**
 
Wow.  You really need to upgrade.
 
> Under a insertion test we get a performance of 2.5 secs under 2000
> inserts (table with a single char(50) column) in the IDE disk.
> And 500GB RAID 0 (4 disks!) and 37.5 secs under the same test!
 
Is each insert in its own database transaction?  (That is you've
done nothing to BEGIN a transaction, do the inserts, and then
COMMIT?)  If so, you're old IDE is lying to PostgreSQL when it says
it has committed each insert.  If you pull the power cord on the
computer a few times during this insert test, you'll find you wind
up missing rows which were supposedly inserted, and you will likely
have database corruption, which might render the database totally
unusable.
 
If you implement your RAID with a good controller which has a
battered backed-up RAM cache, and that is configured to write-back,
you'll see much better performance.
 
Search the archives for BBU and you'll find many other discussions
of this.
 
-Kevin

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