scott.marlowe wrote: > On Fri, 3 Oct 2003, scott.marlowe wrote: > > > On Fri, 3 Oct 2003, Tom Lane wrote: > > > > > > It'd be interesting to think about whether a write-caching IDE drive > > > could safely be used for data storage, if WAL is elsewhere. > > > > Well, I just so happen to have a machine with two drives in it. I'll get > > back to you on that. > > Ok, I just tested it. I put pg_xlog and pg_clog on a drive that was set > to write cache disabled, and left the data on a drive where caching was > enabled. The tps on a pgbench -c 5 -t 500 on the single drive was 45 to > 55. With the pg_[xc]log moved to another drive and all, I got up to 108 > tps. About double performance, as you'd expect. I didn't test the data > drive with write caching disabled, but my guess is it wouldn't be any > slower since pgsql doesn't wait on the rest. > > I pulled the plug three times, and all three times the database came up in > recovery mode and sucessfully recovered. I didn't bother testing to see > if write caching would corrupt it as I'm pretty sure it would, it > certainly did when everything was on one drive.
You would have had to pull the plug between the time the system did a checkpoint (and wrote to the write cache), and before it flushed the write cache to disk --- no idea how you would find that window, but my guess is that if you pulled the plug right after the checkpoint completed, the WAL recovery would fail. -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
