Tom Lane wrote:
So actually, there is no difference between selecting fsync and fsync_writethrough on Windows, this comment and the SGML documentation to the contrary. Both settings result in invoking _commit() and presumably are safe. One wonders why we bothered to invent a separate fsync_writethrough setting on Windows.
Quite; I documented some the details about mapping to _commit() long ago at http://www.westnet.com/~gsmith/content/postgresql/TuningPGWAL.htm but forgot to suggest fixing the mistakes in the docs afterwards (Windows is not exactly my favorite platform). http://archives.postgresql.org/pgsql-hackers/2005-08/msg00227.php explains some of the history I think you're looking for here.
Would someone verify via pgbench or similar test (*not* test_fsync) that on Windows, wal_sync_method = fsync or fsync_writethrough perform the same (ie tps ~= disk rotation rate) while open_datasync is too fast to be real? I'm losing confidence that I've found all the spaghetti ends here, and I don't have a Windows setup to try it myself.
I can look into this tomorrow. The laptop I posted Ubuntu/RHEL6 test_fsync numbers from before also boots into Vista, so I can compare all those platforms on the same hardware. I just need to be aware of the slightly different sequential speeds on each partition of the drive.
As far as your major battle plan goes, I think what we should do is find the simplest possible patch that just fixes the newer Linux kernel problem, preferrably without changing any other platform, then commit that to HEAD and appropriate backports. Then the larger O_DIRECT remapping can proceed forward after that, along with cleanup to the writethrough choices and unifying test_fsync against the server. I wrote a patch that shuffled around a lot of this code last night, but the first thing I coded was junk because of some mistaken assumptions. Have been coming to same realizations about how messy this really is you have.
-- Greg Smith 2ndQuadrant US g...@2ndquadrant.com Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
