Not for WAL --- we never read the WAL at all in normal operation. (IfAt least under Linux, it works for writes. Oracle uses O_DIRECT to access (both read and write) disks that are shared between multiple nodes in a cluster - their database kernel must know when the data is visible to the other nodes.
it works for writes, then we would want to use it for writing WAL, but that's not apparent from what Christopher quoted.)
One problem for WAL is that O_DIRECT would disable the write cache - each operation would block until the data arrived on disk, and that might block other backends that try to access WALWriteLock.
Perhaps a dedicated backend that does the writeback could fix that.
Has anyone tried to use posix_fadvise for the wal logs? http://www.opengroup.org/onlinepubs/007904975/functions/posix_fadvise.html
Linux supports posix_fadvise, it seems to be part of xopen2k.
-- Manfred
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