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:
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?
Thanks
Chris
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