Luke Lonergan wrote: > Why not simply plug your server into a UPS and get 10-20x the performance using the same approach (with OS IO cache)? A big reason is that your machine may already have as much RAM as is currently economical to install. Hardware with LOTS of RAM slots can cost quite a bit. Another reason is that these devices won't lose data because of an unexpected OS reboot. If they're fitted with a battery backup and CF media for emergency write-out, they won't lose data if your UPS runs out of juice either. I'd be much more confident with something like those devices than I would with an OS ramdisk plus startup/shutdown scripts to initialize it from a file and write it out to a file. Wouldn't it be a pain if the UPS didn't give the OS enough warning to write the RAM disk out before losing power... In any case, you're very rarely better off dedicating host memory to a ramdisk rather than using the normal file system and letting the host cache it. A ramdisk really only seems to help when you're really using it to bypass safeties like the effects of fsync() and ordered journaling. There are other ways to avoid those if you really don't care about your data. These devices would be interesting for a few uses, IMO. One is temp table space and sort space in Pg. Another is scratch space for apps (like Photoshop) that do their own VM management. There's also potential for use as 1st priority OS swap space, though at least on Linux I think the CPU overhead involved in swapping is so awful you wouldn't benefit from it much. I've been hoping this sort of thing would turn up again in a new incarnation with battery backup and CF/SD for BBU-flat safety. -- Craig Ringer -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
