From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: PATCH: pgbench - merging transaction logs |
Date: | 2015-03-21 10:04:22 |
Message-ID: | 20150321100422.GB3075@awork2.anarazel.de |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On 2015-03-17 11:50:28 -0400, Robert Haas wrote:
> On Tue, Mar 17, 2015 at 11:27 AM, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)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
From | Date | Subject | |
---|---|---|---|
Next Message | Michael Paquier | 2015-03-21 11:13:00 | Re: GIN code managing entry insertion not able to differentiate fresh and old indexes |
Previous Message | Andres Freund | 2015-03-21 09:50:06 | Re: PATCH: pgbench - merging transaction logs |