Date: Sun, 15 Mar 2020 06:18:31 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: pgsql-hackers@postgresql.org
Cc: Julien Rouhaud <rjuju123@gmail.com>
Subject: expose parallel leader in CSV and log_line_prefix
Message-ID: <20200315111831.GA21492@telsasoft.com>
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See also:
https://commitfest.postgresql.org/27/2390/
https://www.postgresql.org/message-id/flat/CAOBaU_Yy5bt0vTPZ2_LUM6cUcGeqmYNoJ8-Rgto+c2+w3defYA@mail.gmail.com
b025f32e0b Add leader_pid to pg_stat_activity

-- 
Justin

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 filename="v2-0001-Include-the-leader-PID-in-logfile.patch"

From 5268e89fb32fbb639cb39796729dfe0dfcf14705 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Fri, 13 Mar 2020 22:03:06 -0500
Subject: [PATCH v2] 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                | 20 +++++++++++++++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3cac340f32..f6ded2bc45 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -6491,6 +6491,14 @@ 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>
@@ -6789,7 +6797,7 @@ 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>
@@ -6819,6 +6827,7 @@ 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..0f5881355d 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 +2561,18 @@ log_line_prefix(StringInfo buf, ErrorData *edata)
 				else
 					appendStringInfo(buf, "%d", MyProcPid);
 				break;
+
+			case 'k':
+				if (MyBackendType != B_BG_WORKER)
+					; /* Do nothing */
+				else if (!MyProc->lockGroupLeader)
+					; /* Do nothing */
+				else if (padding != 0)
+					appendStringInfo(buf, "%*d", padding, MyProc->lockGroupLeader->pid);
+				else
+					appendStringInfo(buf, "%d", MyProc->lockGroupLeader->pid);
+				break;
+
 			case 'l':
 				if (padding != 0)
 					appendStringInfo(buf, "%*ld", padding, log_line_number);
@@ -2948,6 +2961,13 @@ write_csvlog(ErrorData *edata)
 	else
 		appendCSVLiteral(&buf, GetBackendTypeDesc(MyBackendType));
 
+	appendStringInfoChar(&buf, ',');
+
+	/* leader PID */
+	if (MyBackendType == B_BG_WORKER &&
+			MyProc->lockGroupLeader)
+		appendStringInfo(&buf, "%d", MyProc->lockGroupLeader->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


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