Mark Mielke wrote:
The conclusion I read was that Linux O_SYNC behaves like O_DSYNC on other systems. For WAL, this seems satisfactory?
It would be if it didn't have any bugs or limitiations, but it does. The one pointed out in the message I linked to suggests that a mix of buffered and O_SYNC direct I/O can cause a write error, with the exact behavior you get depending on the kernel version. That's a path better not explored as I see it.
The kernels that have made some effort to implement this correctly actually expose O_DSYNC, on newer Linux systems. My current opinion is that if you only have Linux O_SYNC, don't use it. The ones with O_DSYNC haven't been around for long enough to be proven or disproven as effective yet.
-- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
