Re: Best setup for RAM drive

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