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Re: Ideal disk setup for Postgresql 7.4?

From: Steve Poe <spoe(at)sfnet(dot)cc>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Ideal disk setup for Postgresql 7.4?
Date: 2005-01-25 23:52:56
Message-ID: 41F6DBD8.2050008@sfnet.cc (view raw or flat)
Thread:
Lists: pgsql-performance
Josh,

Thanks for your feedback, I appreciate it.

>Check what I have to say at http://www.powerpostgresql.com/PerfList
>  
>
Will do.

>>They're currently on a two-disk Adaptec RAID1 with Postgresql 7.4.2.
>>    
>>
>
>And you've not upgraded to 7.4.6 because .... ?
>
>  
>
Because the proprietary application running the business has not 
certified on it.  Unfortunately, I am at the mercy of their support in 
case something goes wrong.

>>The drive array is a 7-disk fibre channel on a Qlogic 2100 controller. I
>>am currently testing RAID5 (sw).
>>    
>>
>
>In general, RAID 5 is not so great for databases.  See the article for more.
>
>  
>
Okay, thanks. Even with 7-disks? I trust that. So, RAID 1+0 (sw) is 
probably the best option. I've run sw RAID personally for years without 
issue. I am a bit hesitant in doing sw RAID for a production server for 
a database --- probably because its not my server. Any thoughts on sw 
RAID for Postgresql?

>>The main reason of moving to a drive array is the high level of context
>>switches we get during the day (>30K for 20 mins per hour). The OS and
>>database exist on the same disk but seperate parition (which probably
>>makes little difference)
>>    
>>
>
>Unfortunately, the context switches are probably due to a known issue in 
>PostgreSQL, and changing the drive array won't help this issue (it may help 
>other issues though).    Search the archives of this list, and pgsql-hackers, 
>for "Context Switch Bug".
>
>For the CS bug, the only workaround right now is to avoid the query structures 
>that trigger it.
>  
>
Okay. Darn. While I don't write the queries for the application, I do 
interact with the company frequently. Their considering moving the 
queries into the database with PL/pgSQL. Currently their queries are 
done through ProvIV development using ODBC. Will context switching be 
minimized here by using PL/pgSQL?

>  
>
>>Server Info:
>>Centos 3.3 (RHEL 3.x equivelent)
>>4GB RAM
>>Adaptec 2100S RAID
>>Qlogic QLA2100 Fibre
>>    
>>
>
>CPU?
>  
>
Dual Xeon 2.8 CPUs with HT turned off.


Thanks again.

Steve Poe

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