On Wed, 25 Jun 2008, Peter T. Breuer wrote:
I refrained from saying in my reply that I would set up a firewire-based link to ram in a spare old portable (which comes with a battery) if I wanted to do this cheaply.
Maybe, but this is kind of a weird setup. Not many people are going to run a production database that way and us wandering into the details too much risks confusing everybody else.
The log is sync. Therefore it doesn't matter what the guarantees are, or at least I assume you are worrying about acks coming back before the write has been sent, etc. Only an actual net write will be acked by the firewire transport as far as I know.
That's exactly the issue; it's critical for database use that a disk not lie to you about writes being done if they're actually sitting in a cache somewhere. (S)ATA disks do that, so you have to turn that off for them to be safe to use. Since the firewire enclosure is a black box, it's difficult to know exactly what it's doing here, and history here says that every type (S)ATA disk does the wrong in the default case. I expect that for any Firewire/USB device, if I write to the disk, then issue a fsync, it will return success from that once the data has been written to the disk's cache--which is crippling behavior from the database's perspective one day when you get a crash.
-- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
