Date: Sun, 26 Jul 2020 13:54:27 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
	Julien Rouhaud <rjuju123@gmail.com>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	pgsql-hackers@postgresql.org
Subject: Re: expose parallel leader in CSV and log_line_prefix
Message-ID: <20200726185427.GI4286@telsasoft.com>
References: <20200721043325.GC17300@paquier.xyz>
 <20200722153605.GA961@alvherre.pgsql>
 <20200723005214.GD26630@paquier.xyz>
 <20200726074206.GB4351@paquier.xyz>
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On Sun, Jul 26, 2020 at 04:42:06PM +0900, Michael Paquier wrote:
> On Thu, Jul 23, 2020 at 09:52:14AM +0900, Michael Paquier wrote:
> > Sounds fine to me.  Thanks.
> > 
> > Do others have any objections with this wording?
> 
> I have used the wording suggested by Alvaro, and applied the patch
> down to 13.  Now let's see about the original item of this thread..

Updated with updated wording to avoid "null", per Tom.

-- 
Justin

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 filename="v3-0001-Include-the-leader-PID-in-logfile.patch"

From 665c9ea8827d4ad94ea0100c5ba93dbf05db5943 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Fri, 13 Mar 2020 22:03:06 -0500
Subject: [PATCH v3] Include the leader PID in logfile

See also: b025f32e0b, which adds the leader PID to pg_stat_activity
---
 doc/src/sgml/config.sgml                      | 10 ++++++-
 src/backend/utils/error/elog.c                | 30 +++++++++++++++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e806b13754..c525a0fd15 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -6687,6 +6687,13 @@ local0.*    /var/log/postgresql
              <entry>Process ID</entry>
              <entry>no</entry>
             </row>
+            <row>
+             <entry><literal>%P</literal></entry>
+             <entry>For a parallel worker, this is the Process ID of its leader
+             process.
+             </entry>
+             <entry>no</entry>
+            </row>
             <row>
              <entry><literal>%t</literal></entry>
              <entry>Time stamp without milliseconds</entry>
@@ -7019,7 +7026,7 @@ log_line_prefix = '%m [%p] %q%u@%d/%a '
         character count of the error position therein,
         location of the error in the PostgreSQL source code
         (if <varname>log_error_verbosity</varname> is set to <literal>verbose</literal>),
-        application name, and backend type.
+        application name, backend type, and leader PID.
         Here is a sample table definition for storing CSV-format log output:
 
 <programlisting>
@@ -7049,6 +7056,7 @@ CREATE TABLE postgres_log
   location text,
   application_name text,
   backend_type text,
+  leader_pid integer,
   PRIMARY KEY (session_id, session_line_num)
 );
 </programlisting>
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index e4b717c79a..3055b72c01 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -77,6 +77,7 @@
 #include "postmaster/syslogger.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
+#include "storage/procarray.h"
 #include "tcop/tcopprot.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
@@ -2448,6 +2449,25 @@ log_line_prefix(StringInfo buf, ErrorData *edata)
 				else
 					appendStringInfo(buf, "%d", MyProcPid);
 				break;
+
+			case 'P':
+				if (MyProc)
+				{
+					PGPROC *leader = MyProc->lockGroupLeader;
+					if (leader == NULL || leader->pid == MyProcPid)
+						/* padding only */
+						appendStringInfoSpaces(buf,
+								padding > 0 ? padding : -padding);
+					else if (padding != 0)
+						appendStringInfo(buf, "%*d", padding, leader->pid);
+					else
+						appendStringInfo(buf, "%d", leader->pid);
+				}
+				else if (padding != 0)
+					appendStringInfoSpaces(buf,
+										   padding > 0 ? padding : -padding);
+				break;
+
 			case 'l':
 				if (padding != 0)
 					appendStringInfo(buf, "%*ld", padding, log_line_number);
@@ -2836,6 +2856,16 @@ write_csvlog(ErrorData *edata)
 	else
 		appendCSVLiteral(&buf, GetBackendTypeDesc(MyBackendType));
 
+	appendStringInfoChar(&buf, ',');
+
+	/* leader PID */
+	if (MyProc)
+	{
+		PGPROC *leader = MyProc->lockGroupLeader;
+		if (leader && leader->pid != MyProcPid)
+			appendStringInfo(&buf, "%d", leader->pid);
+	}
+
 	appendStringInfoChar(&buf, '\n');
 
 	/* If in the syslogger process, try to write messages direct to file */
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index aa30291ea3..55c2e23c47 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -536,6 +536,7 @@
 					#   %h = remote host
 					#   %b = backend type
 					#   %p = process ID
+					#   %P = leader PID
 					#   %t = timestamp without milliseconds
 					#   %m = timestamp with milliseconds
 					#   %n = timestamp with milliseconds (as a Unix epoch)
-- 
2.17.0


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