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Re: Best setup for RAM drive

From: Hannu Krosing <hannu(at)tm(dot)ee>
To: Chris Sutton <chris(at)smoothcorp(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Best setup for RAM drive
Date: 2003-03-04 20:57:27
Message-ID: 1046811447.1681.3.camel@fuji.krosing.net (view raw or flat)
Thread:
Lists: pgsql-hackers
Chris Sutton kirjutas T, 04.03.2003 kell 17:03:
> Hello,
> 
> I need some insight on the best way to use a RAM drive in a Postgresql 
> installation.  Here is our situation and current setup:
> 
> Postgresql 7.2.1
> Dual PIII 800
> RAID 5 SCSI disks
> Platypus 8GB PCI QikDrive (the RAM drive).  http://www.platypus.net
> 
> The Platypus RAM drive is a PCI card with 8GB of ram onboard with an 
> external power supply so if the main power to the server goes off, the RAM 
> is still powered, so it's persistent between reboots.
> 
> Currently the disk size of our database is 3.2GB, so we put the whole 
> pgsql directory on the RAM drive.  Current preformance is very 
> snappy with the bottleneck being the CPUs.  
> 
> The concern of course is if something happends to the RAM drive we are 
> S.O.L. and have to go to the last backup (pg_dump happens each night).
> 
> The other concern is if the disk size of the database grows past or near 
> 8gb, we would either have to get a bigger RAM drive or somehow split 
> things betten SCSI and RAM drive.
> 
> I don't quite grasp the full inner workings of Postgresql, but 
> for those of you who obviously do, is there a better way of setting things 
> up where you could still use the RAM drive for portions of the pgsql 
> directory structure while putting the rest on disk where it's safer?
> 
> Should we just put pgsql/data/pg_xlog on the RAM drive?
> 
> Also, in the very near future we will be upgrading to another server, 
> pg7.3.2 with dual P4 2.4 xenon's.  The RAM drive will go into this new 
> server.
> 
> Any suggestions?

The most obvious suggestion is to put the WAL files on RAM disk - these
are the things that would most directly affect _write_ performance as
these are the only ones the *must* hit the disk befor the transaction
can be committed.

If you are after read performance, then you just ;) have to determine
which are the most frequently used files that are not reasonably cached
.

---------------
Hannu








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