Date: Fri, 10 Jul 2020 11:55:25 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Julien Rouhaud <rjuju123@gmail.com>, pgsql-hackers@postgresql.org
Subject: Re: expose parallel leader in CSV and log_line_prefix
Message-ID: <20200710165524.GL26220@telsasoft.com>
References: <20200318212511.GN26184@telsasoft.com>
 <20200710164529.GA23646@alvherre.pgsql>
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On Fri, Jul 10, 2020 at 12:45:29PM -0400, Alvaro Herrera wrote:
> On 2020-Mar-18, Justin Pryzby wrote:
> 
> > On Sun, Mar 15, 2020 at 12:49:33PM +0100, Julien Rouhaud wrote:
> 
> > template1=# SET log_temp_files=0; explain analyze SELECT a,COUNT(1) FROM t a JOIN t b USING(a) GROUP BY 1;
> > 2020-03-15 21:20:47.288 CDT [5537        5537]LOG:  statement: SET log_temp_files=0;
> > SET
> > 2020-03-15 21:20:47.289 CDT [5537        5537]LOG:  statement: explain analyze SELECT a,COUNT(1) FROM t a JOIN t b USING(a) GROUP BY 1;
> > 2020-03-15 21:20:51.253 CDT [5627        5537]LOG:  temporary file: path "base/pgsql_tmp/pgsql_tmp5627.0", size 6094848
> > 2020-03-15 21:20:51.253 CDT [5627        5537]STATEMENT:  explain analyze SELECT a,COUNT(1) FROM t a JOIN t b USING(a) GROUP BY 1;
> > 2020-03-15 21:20:51.254 CDT [5626        5537]LOG:  temporary file: path "base/pgsql_tmp/pgsql_tmp5626.0", size 6103040
> > 2020-03-15 21:20:51.254 CDT [5626        5537]STATEMENT:  explain analyze SELECT a,COUNT(1) FROM t a JOIN t b USING(a) GROUP BY 1;
> > 2020-03-15 21:20:51.263 CDT [5537        5537]LOG:  temporary file: path "base/pgsql_tmp/pgsql_tmp5537.1.sharedfileset/o15of16.p0.0", size 557056
> 
> I think it's overly verbose; all non-parallel backends are going to get
> their own PID twice, and I'm not sure this is going to be great to
> parse.  I think it would be more sensible that if the process does not
> have a parent (leader), %P expands to empty.

That's what's done.

+             <entry>Process ID of the parallel group leader if this process was
+             at some point involved in parallel query, otherwise null.  For a
+             parallel group leader itself, this field is set to its own process
+             ID.</entry>

2020-07-10 11:53:32.304 CDT [16699 ]LOG:  statement: SELECT 1;
2020-07-10 11:53:32.304 CDT,"pryzbyj","postgres",16699,"[local]",5f089d0b.413b,1,"idle",2020-07-10 11:53:31 CDT,3/4,0,LOG,00000,"statement: SELECT 1;",,,,,,,,,"psql","client backend",

-- 
Justin