v2-0001-Remove-pg_wait_for_backend_termination-function.patch

From 157c17195b085907c19d4c935cc28076a2aca56c Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Mon, 14 Jun 2021 07:00:09 -0700
Subject: [PATCH v2] Remove pg_wait_for_backend_termination function

It was unable to wait on a backend that had already left the
procarray. Users tolerant of that limitation can poll
pg_stat_activity.  Other users can employ the "timeout" argument
of pg_terminate_backend function.

Per suggestion from Justin Pryzby, reworded the docs, code comments
and release notes relating to the pg_terminate_backend function.
---
 doc/src/sgml/func.sgml                   | 19 +--------
 doc/src/sgml/release-14.sgml             |  8 +---
 src/backend/catalog/system_functions.sql |  5 ---
 src/backend/storage/ipc/signalfuncs.c    | 50 ++++--------------------
 src/include/catalog/pg_proc.dat          |  6 +--
 5 files changed, 10 insertions(+), 78 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index fbc80c1403..764c3ad307 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -24998,27 +24998,10 @@ SELECT collation for ('foo' COLLATE "de_DE");
         milliseconds) and greater than zero, the function waits until the
         process is actually terminated or until the given time has passed. If
         the process is terminated, the function
-        returns <literal>true</literal>.  On timeout a warning is emitted and
+        returns <literal>true</literal>.  On timeout, a warning is emitted and
         <literal>false</literal> is returned.
        </para></entry>
       </row>
-
-      <row>
-       <entry role="func_table_entry"><para role="func_signature">
-        <indexterm>
-         <primary>pg_wait_for_backend_termination</primary>
-        </indexterm>
-        <function>pg_wait_for_backend_termination</function> ( <parameter>pid</parameter> <type>integer</type>, <parameter>timeout</parameter> <type>bigint</type> <literal>DEFAULT</literal> <literal>5000</literal> )
-        <returnvalue>boolean</returnvalue>
-       </para>
-       <para>
-        Waits for the backend process with the specified Process ID to
-        terminate.  If the process terminates before
-        the <parameter>timeout</parameter> (in milliseconds)
-        expires, <literal>true</literal> is returned.  On timeout, a warning
-        is emitted and <literal>false</literal> is returned.
-       </para></entry>
-      </row>
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/release-14.sgml b/doc/src/sgml/release-14.sgml
index 058ba7cd4e..89bf78500a 100644
--- a/doc/src/sgml/release-14.sgml
+++ b/doc/src/sgml/release-14.sgml
@@ -611,13 +611,7 @@ Author: Magnus Hagander <magnus@hagander.net>
 -->
 
       <para>
-       Add function <link
-       linkend="functions-admin-signal"><function>pg_wait_for_backend_termination()</function></link>
-       that waits for session exit (Bharath Rupireddy)
-      </para>
-
-      <para>
-       Also add a similar optional wait parameter to <link
+       Add an optional timeout parameter to <link
        linkend="functions-admin-signal"><function>pg_terminate_backend()</function></link>
       </para>
      </listitem>
diff --git a/src/backend/catalog/system_functions.sql b/src/backend/catalog/system_functions.sql
index a4373b176c..a416e94d37 100644
--- a/src/backend/catalog/system_functions.sql
+++ b/src/backend/catalog/system_functions.sql
@@ -397,11 +397,6 @@ CREATE OR REPLACE FUNCTION
   RETURNS boolean STRICT VOLATILE LANGUAGE INTERNAL AS 'pg_terminate_backend'
   PARALLEL SAFE;
 
-CREATE OR REPLACE FUNCTION
-  pg_wait_for_backend_termination(pid integer, timeout int8 DEFAULT 5000)
-  RETURNS boolean STRICT VOLATILE LANGUAGE INTERNAL AS 'pg_wait_for_backend_termination'
-  PARALLEL SAFE;
-
 -- legacy definition for compatibility with 9.3
 CREATE OR REPLACE FUNCTION
   json_populate_record(base anyelement, from_json json, use_json_as_text boolean DEFAULT false)
diff --git a/src/backend/storage/ipc/signalfuncs.c b/src/backend/storage/ipc/signalfuncs.c
index 837699481c..30c4516f8d 100644
--- a/src/backend/storage/ipc/signalfuncs.c
+++ b/src/backend/storage/ipc/signalfuncs.c
@@ -187,12 +187,12 @@ pg_wait_until_termination(int pid, int64 timeout)
 }
 
 /*
- * Signal to terminate a backend process. This is allowed if you are a member
- * of the role whose process is being terminated. If timeout input argument is
- * 0 (which is default), then this function just signals the backend and
- * doesn't wait. Otherwise it waits until given the timeout milliseconds or no
- * process has the given PID and returns true. On timeout, a warning is emitted
- * and false is returned.
+ * Send a signal to terminate a backend process. This is allowed if you are a
+ * member of the role whose process is being terminated. If the timeout input
+ * argument is 0, then this function just signals the backend and returns true.
+ * If timeout is nonzero, then it waits until no process has the given PID; if
+ * the process ends within the timeout, true is returned, and if the timeout is
+ * exceeded, a warning is emitted and false is returned.
  *
  * Note that only superusers can signal superuser-owned processes.
  */
@@ -201,7 +201,7 @@ pg_terminate_backend(PG_FUNCTION_ARGS)
 {
 	int			pid;
 	int			r;
-	int			timeout;
+	int			timeout;  /* milliseconds */
 
 	pid = PG_GETARG_INT32(0);
 	timeout = PG_GETARG_INT64(1);
@@ -230,42 +230,6 @@ pg_terminate_backend(PG_FUNCTION_ARGS)
 		PG_RETURN_BOOL(r == SIGNAL_BACKEND_SUCCESS);
 }
 
-/*
- * Wait for a backend process with the given PID to exit or until the given
- * timeout milliseconds occurs. Returns true if the backend has exited. On
- * timeout a warning is emitted and false is returned.
- *
- * We allow any user to call this function, consistent with any user being
- * able to view the pid of the process in pg_stat_activity etc.
- */
-Datum
-pg_wait_for_backend_termination(PG_FUNCTION_ARGS)
-{
-	int			pid;
-	int64		timeout;
-	PGPROC	   *proc = NULL;
-
-	pid = PG_GETARG_INT32(0);
-	timeout = PG_GETARG_INT64(1);
-
-	if (timeout <= 0)
-		ereport(ERROR,
-				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
-				 errmsg("\"timeout\" must not be negative or zero")));
-
-	proc = BackendPidGetProc(pid);
-
-	if (proc == NULL)
-	{
-		ereport(WARNING,
-				(errmsg("PID %d is not a PostgreSQL server process", pid)));
-
-		PG_RETURN_BOOL(false);
-	}
-
-	PG_RETURN_BOOL(pg_wait_until_termination(pid, timeout));
-}
-
 /*
  * Signal to reload the database configuration
  *
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index acbcae4607..8acb39aa7b 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -6187,14 +6187,10 @@
   proname => 'pg_cancel_backend', provolatile => 'v', prorettype => 'bool',
   proargtypes => 'int4', prosrc => 'pg_cancel_backend' },
 { oid => '2096',
-  descr => 'terminate a backend process and if timeout is specified, wait for its exit or until timeout occurs',
+  descr => 'terminate a server process',
   proname => 'pg_terminate_backend', provolatile => 'v', prorettype => 'bool',
   proargtypes => 'int4 int8', proargnames => '{pid,timeout}',
   prosrc => 'pg_terminate_backend' },
-{ oid => '2137', descr => 'wait for a backend process exit or timeout occurs',
-  proname => 'pg_wait_for_backend_termination', provolatile => 'v',
-  prorettype => 'bool', proargtypes => 'int4 int8',
-  proargnames => '{pid,timeout}', prosrc => 'pg_wait_for_backend_termination' },
 { oid => '2172', descr => 'prepare for taking an online backup',
   proname => 'pg_start_backup', provolatile => 'v', proparallel => 'r',
   prorettype => 'pg_lsn', proargtypes => 'text bool bool',
-- 
2.25.1