From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> |
Cc: | Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: System load consideration before spawning parallel workers |
Date: | 2016-09-01 17:16:37 |
Message-ID: | 28787.1472750197@sss.pgh.pa.us |
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Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> writes:
> As I just wrote in another message in this thread, I don't trust system
> load metrics very much as a gatekeeper. They are reasonable for
> long-term charting to discover trends, but there are numerous potential
> problems for using them for this kind of resource control thing.
As a note in support of that, sendmail has a "feature" to suppress service
if system load gets above X, which I have never found to do anything
except result in self-DOSing. The load spike might not have anything to
do with the service that is trying to un-spike things. Even if it does,
Peter is correct to note that the response delay is much too long to form
part of a useful feedback loop. It could be all right for scheduling
activities whose length is comparable to the load average measurement
interval, but not for short-term decisions.
regards, tom lane
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