On Tue, 19 May 2009, Pal, Dipali (UMKC-Student) wrote:
Which of the recent versions of postgresql support direct I/O?
As of 8.1 PostgreSQL does direct I/O for writes to the WAL if you've configured wal_sync_method={open_datasync,open_sync} on supported platforms. I know Linux works but Solaris doesn't. See http://www.postgresql.org/docs/current/static/runtime-config-wal.html#GUC-WAL-SYNC-METHOD and http://www.postgresql.org/docs/current/static/wal-configuration.html for more details. The usual workaround for the Solaris problem is to split the WAL pg_xlog directory onto another filesystem and change its mounting options, see http://blogs.sun.com/jkshah/entry/postgresql_wal_sync_method_and for more about that.
There is no option to do direct writes for the main database I/O because the database usually performs better if you rely on the filesystem cache. You can certainly find situations where sync writes end up working out better, but they're not common.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
