On 2015-03-17 11:50:28 -0400, Robert Haas wrote: > On Tue, Mar 17, 2015 at 11:27 AM, Fabien COELHO <coe...@cri.ensmp.fr> wrote: > > The fprintf we are talking about occurs at most once per pgbench > > transaction, possibly much less when aggregation is activated, and this > > transaction involves networks exchanges and possibly disk writes on the > > server. > > random() was occurring four times per transaction rather than once, > but OTOH I think fprintf() is probably a much heavier-weight > operation. The way to know if there's a real problem here is to test > it, but I'd be pretty surprised if there isn't.
Well, fprintf() doesn't have to acquire the lock for the entirety of it's operation - just for the access to the stream buffer. Note that posix 2001 *does* guarantee that FILE* style IO is thread safe: "All functions that reference (FILE *) objects, except those with names ending in _unlocked, shall behave as if they use flockfile() and funlockfile() internally to obtain ownership of these (FILE *) objects." Hilariously that tidbit hidden in the documentation about flockfile. Very, err, easy to find: http://pubs.opengroup.org/onlinepubs/9699919799/functions/flockfile.html But I agree that we simply need to test this on a larger machine. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
