Re: PATCH: pgbench - merging transaction logs

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: PATCH: pgbench - merging transaction logs
Date: 2015-03-23 19:00:04
Message-ID: alpine.DEB.2.10.1503231924320.29534@sto
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> Guys, I don't see this theoretical discussion going anywhere. I think
> it's time to simply implement this and evaluate it on a bigger
> machine.

Sure. I was kind of hoping that someone else would implement it, because
I'm a reviewer on this one, and I do not have the bigger machine at hand
either:-) If nothing happens and when I have some time, I'll do it.

> It can't take very long to implement tosimply just write to one
> file instead of the multiple files as now.

Sure.

> The posix guaranteed fprintf locking should already take care of the
> rest.

I think I would try with snprintf to reduce locking.

Note that I'm first trying to evaluate logging overhead, but I'm quite far
from Tomas figures at the moment, looks more like 20% overhead (12 threads
read-only load, runs at about 130000 tps with full logging, 160000
without, repeated 5 times with the similar results).

In such a case, a mutex would be a bad idea, but I must add that detailed
logging is a plain bad idea as well!

--
Fabien.

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