> Mac OS X: Like Solaris, there's a similar mechanism but it's not > O_DIRECT; see > http://stackoverflow.com/questions/2299402/how-does-one-do-raw-io-on-mac-os-x-ie-equivalent-to-linuxs-o-direct-flag > for notes about the F_NOCACHE feature used. Same basic situation as > Solaris; there's an API, but PostgreSQL doesn't use it yet.
Actually, on OSX 10.5.8, o_dsync and fdatasync aren't even available. >From my run, it looks like even so regular fsync might be better than open_sync. Results from a MacBook: Sidney-Stratton:fsync josh$ ./test_fsync Loops = 10000 Simple write: 8k write 2121.004/second Compare file sync methods using one write: (open_datasync unavailable) open_sync 8k write 1993.833/second (fdatasync unavailable) 8k write, fsync 1878.154/second Compare file sync methods using two writes: (open_datasync unavailable) 2 open_sync 8k writes 1005.009/second (fdatasync unavailable) 8k write, 8k write, fsync 1709.862/second Compare open_sync with different sizes: open_sync 16k write 1728.803/second 2 open_sync 8k writes 969.416/second Test if fsync on non-write file descriptor is honored: (If the times are similar, fsync() can sync data written on a different descriptor.) 8k write, fsync, close 1772.572/second 8k write, close, fsync 1939.897/second -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers