From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
---|---|
To: | Jan Wieck <jan(at)wi3ck(dot)info>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
Cc: | Rukh Meski <rukh(dot)meski(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: pgbench throttling latency limit |
Date: | 2014-09-09 11:12:33 |
Message-ID: | 540EE0A1.5070704@vmware.com |
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Lists: | pgsql-hackers |
On 09/09/2014 01:49 PM, Heikki Linnakangas wrote:
> I think we have to reconsider what we're reporting in 9.4, when --rate
> is enabled, even though it's already very late in the release cycle.
> It's a bad idea to change the definition of latency between 9.4 and 9.5,
> so let's get it right in 9.4.
As per the attached patch. I think we should commit this to 9.4. Any
objections?
The text this patch adds to the documentation needs some rewording,
though. As does this existing paragraph:
> High rate limit schedule lag values, that is lag values that are
> large compared to the actual transaction latency, indicate that
> something is amiss in the throttling process. High schedule lag can
> highlight a subtle problem there even if the target rate limit is met
> in the end. One possible cause of schedule lag is insufficient
> pgbench threads to handle all of the clients. 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.
It took me ages to parse "high rate limit schedule lag values".
- Heikki
Attachment | Content-Type | Size |
---|---|---|
pgbench-calculate-latency-from-scheduled-time.patch | text/x-diff | 2.7 KB |
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