Date: Tue, 10 Mar 2020 14:01:43 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Julien Rouhaud <rjuju123@gmail.com>,
	Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: backend type in log_line_prefix?
Message-ID: <20200310190142.GB29065@telsasoft.com>
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On Thu, Feb 13, 2020 at 06:43:32PM +0900, Fujii Masao wrote:
> If we do this, backend type should be also included in csvlog?

+1, I've been missing that

Note, this patch seems to correspond to:
b025f32e0b Add leader_pid to pg_stat_activity

I had mentioned privately to Julien missing this info in CSV log.

Should leader_pid be exposed instead (or in addition)?  Or backend_type be a
positive number giving the leader's PID if it's a parallel worker, or a some
special negative number like -BackendType to indicate a nonparallel worker.
NULL for a B_BACKEND which is not a parallel worker.

My hope is to answer to questions like these:

. is query (ever? usually?) using parallel paths?
. is query usefully using parallel paths?
. what queries are my max_parallel_workers(_per_process) being used for ?
. Are certain longrunning or frequently running queries which are using
  parallel paths using all max_parallel_workers and precluding other queries
  from using parallel query ?  Or, are semi-short queries sometimes precluding
  longrunning queries from using parallelism, when the long queries would
  better benefit ?

I think this patch alone wouldn't provide that, and there'd need to either be a
line logged for each worker.  Maybe it'd log full query+details (ugh), or just
log "parallel worker of pid...".  Or maybe there'd be a new column with which
the leader would log nworkers (workers planned vs workers launched - I would
*not* want to get this out of autoexplain).

-- 
Justin