Date: Fri, 10 Jul 2020 12:45:29 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Julien Rouhaud <rjuju123@gmail.com>, pgsql-hackers@postgresql.org
Subject: Re: expose parallel leader in CSV and log_line_prefix
Message-ID: <20200710164529.GA23646@alvherre.pgsql>
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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.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services