Bruce Momjian wrote: > Greg Smith wrote: >> .... If you have a regular SATA drive, it almost certainly >> supports proper cache flushing.... > > OK, but I have a few questions. Is a write to the drive and a cache > flush command the same? I believe they're different as of ATAPI-6 from 2001. > Which file systems implement both? Seems ZFS and recent ext4 have thought these interactions out thoroughly. Find a slow ext4 that people complain about, and that's the one doing it right :-). Ext3 has some particularly odd annoyances where it flushes and waits for certain writes (ones involving inode changes) but doesn't bother to flush others (just data changes). As far as I can tell, with ext3 you need userspace utilities to make sure flushes occur when you need them. At one point I was tempted to try to put such userspace hacks into postgres. I know less about other file systems. Apparently the NTFS guys are aware of such stuff - but don't know what kinds of fsync equivalent you'd need to make it happen. Also worth noting - Linux's software raid stuff (MD and LVM) need to handle this right as well - and last I checked (sometime last year) the default setups didn't. > I thought a > write to the drive was always assumed to flush it to the platters, > assuming the drive's cache is set to write-through. Apparently somewhere around here: http://www.t10.org/t13/project/d1410r3a-ATA-ATAPI-6.pdf they were separated in the IDE world. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
