From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Greg Smith <greg(at)2ndQuadrant(dot)com> |
Cc: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Tatsuo Ishii <ishii(at)postgresql(dot)org>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [PATCH] pgbench --throttle (submission 7 - with lag measurement) |
Date: | 2013-07-22 16:44:17 |
Message-ID: | 20130722164416.GC3795@eldon.alvh.no-ip.org |
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Lists: | pgsql-hackers |
Greg Smith wrote:
Thanks. I didn't look at the code, but while trying to read the docs:
> + <para>
> + High rate limit schedule lag values, that is values not small with
> + respect to the actual transaction latency, indicate that something is
> + amiss in the throttling process.
I couldn't really parse the above. Of the first six words, which one is
a verb? Is there a noun that needs to be plural? Is there a word that
shouldn't be there?
... Oh, I think it makes sense if I assume that "rate limit schedule lag"
is a single concept .. but if so, that phrase seems too many words for it.
(So when the RLSL values are high, this indicates a problem. Is that
what the above means?)
Also, it took me a while to understand what "values not small" means. I
think there must be a way to phrase this that's easier to understand.
> High lag can highlight a subtle
> + problem there even if the target rate limit is met in the end. One
> + possible cause of schedule lage is insufficient pgbench threads to
> + handle all of the clients.
typo "lage" above.
> To improve that, consider reducing the
> + number of clients, increasing the number of threads in pgbench, or
> + running pgbench on a separate host. Another possibility is that the
> + database is not keeping up with the load at some point. When that
> + happens, you will have to reduce the expected transaction rate to
> + lower schedule lag.
> + </para>
Thanks
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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