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Re: Best setup for RAM drive

From: mlw <pgsql(at)mohawksoft(dot)com>
To: Chris Sutton <chris(at)smoothcorp(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Best setup for RAM drive
Date: 2003-03-05 20:05:03
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
The idea of a RAM disk based database and reliable storage are in 
complete opposition. Forget it.

The question is: What do you need the *raw* speed of a RAM disk for, and 
what can you tollerate for overhead for reliability?

You have posed a question about how to implement a flawed solution, what 
is the original problem you are intending to solve?

Chris Sutton wrote:

>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).
>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 
>Any suggestions?
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