Date: Fri, 24 Nov 2017 12:21:51 +0100
From: hubert depesz lubaczewski <depesz@depesz.com>
To: pgsql-hackers mailing list <pgsql-hackers@postgresql.org>
Subject: explain analyze output with parallel workers - question about
 meaning of information for explain.depesz.com
Message-ID: <20171124112151.GA6616@depesz.com>
Reply-To: depesz@depesz.com
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Hi,

up to parallel executions, when we had node in explain analyze showing
"loops=x" with x more than 1, it meant that the "actual time" had to be
multiplied by loops to get real time spent in a node.

For example, check step 13 in https://explain.depesz.com/s/gNBd

It shows time of 3ms, but loops of 1873, so the actual time is ~ 5600ms.

But with parallel execution it seems to be no longer the case.

For example:
https://explain.depesz.com/s/LTMp
or
https://explain.depesz.com/s/QHRi

It looks that the actual time is really actual time, and loops is
"worker nodes + 1".

Is that really the case? Should I, for explain.depesz.com, when dealing
with partial* and parallel* nodes, use "loops=1" for calculation of
exclusive/inclusive time? always? some other nodes?

or am I missing something in here?

Best regards,

depesz