From 53d766e88537ca018d46efc671d5b586862fb30b 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                      | 11 +++++++-
 src/backend/utils/error/elog.c                | 27 +++++++++++++++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 672bf6f1ee..b9a1bd9a31 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -6511,6 +6511,14 @@ local0.*    /var/log/postgresql
              <entry>Process ID</entry>
              <entry>no</entry>
             </row>
+            <row>
+             <entry><literal>%k</literal></entry>
+             <entry>Process ID of the parallel group leader if this
+             process is or was involved in parallel query, null
+             otherwise.  For a parallel group leader, this field is
+             set to its own process ID.</entry>
+             <entry>no</entry>
+            </row>
             <row>
              <entry><literal>%t</literal></entry>
              <entry>Time stamp without milliseconds</entry>
@@ -6809,7 +6817,7 @@ 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>
@@ -6839,6 +6847,7 @@ 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 62eef7b71f..5328664f4d 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"
@@ -2560,6 +2561,22 @@ log_line_prefix(StringInfo buf, ErrorData *edata)
 				else
 					appendStringInfo(buf, "%d", MyProcPid);
 				break;
+
+			case 'k':
+				if (MyProc)
+				{
+					PGPROC *leader = MyProc->lockGroupLeader;
+					if (leader == NULL)
+						/* padding only */
+						appendStringInfoSpaces(buf,
+								padding > 0 ? padding : -padding);
+					else if (padding != 0)
+						appendStringInfo(buf, "%*d", padding, leader->pid);
+					else
+						appendStringInfo(buf, "%d", leader->pid);
+				}
+				break;
+
 			case 'l':
 				if (padding != 0)
 					appendStringInfo(buf, "%*ld", padding, log_line_number);
@@ -2948,6 +2965,16 @@ write_csvlog(ErrorData *edata)
 	else
 		appendCSVLiteral(&buf, GetBackendTypeDesc(MyBackendType));
 
+	appendStringInfoChar(&buf, ',');
+
+	/* leader PID */
+	if (MyProc)
+	{
+		PGPROC *leader = MyProc->lockGroupLeader;
+		if (leader)
+			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 aa44f0c9bf..6874792a15 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -530,6 +530,7 @@
 					#   %h = remote host
 					#   %b = backend type
 					#   %p = process ID
+					#   %k = leader PID
 					#   %t = timestamp without milliseconds
 					#   %m = timestamp with milliseconds
 					#   %n = timestamp with milliseconds (as a Unix epoch)
-- 
2.17.0