Allow UNLISTEN in hot-standby mode.

tglsfdc · tglsfdc · commit 0d5b27351225 · 2019-01-25T21:14:31.000-05:00
Since LISTEN is (still) disallowed, UNLISTEN must be a no-op in a hot-standby session, and so there's no harm in allowing it. This change allows client code to not worry about whether it's connected to a primary or standby server when performing session-state-reset type activities. (Note that DISCARD ALL, which includes UNLISTEN, was already allowed, making it inconsistent to reject UNLISTEN.) Per discussion, back-patch to all supported versions. Shay Rojansky, reviewed by Mi Tar Discussion: https://postgr.es/m/CADT4RqCf2gA_TJtPAjnGzkC3ZiexfBZiLmA-mV66e4UyuVv8bA@mail.gmail.com
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
@@ -1686,6 +1686,11 @@ if (!triggered)
        Plugins and extensions - <command>LOAD</>
       </para>
      </listitem>
+     <listitem>
+      <para>
+       <command>UNLISTEN</command>
+      </para>
+     </listitem>
     </itemizedlist>
    </para>
 
@@ -1775,16 +1780,16 @@ if (!triggered)
      </listitem>
      <listitem>
       <para>
-       <command>LISTEN</>, <command>UNLISTEN</>, <command>NOTIFY</>
+       <command>LISTEN</>, <command>NOTIFY</>
       </para>
      </listitem>
     </itemizedlist>
    </para>
 
    <para>
     In normal operation, <quote>read-only</> transactions are allowed to
-    use <command>LISTEN</>, <command>UNLISTEN</>, and
-    <command>NOTIFY</>, so Hot Standby sessions operate under slightly tighter
+    use <command>LISTEN</command> and <command>NOTIFY</command>,
+    so Hot Standby sessions operate under slightly tighter
     restrictions than ordinary read-only sessions.  It is possible that some
     of these restrictions might be loosened in a future release.
    </para>
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
@@ -621,7 +621,7 @@ standard_ProcessUtility(Node *parsetree,
 			{
 				UnlistenStmt *stmt = (UnlistenStmt *) parsetree;
 
-				PreventCommandDuringRecovery("UNLISTEN");
+				/* we allow UNLISTEN during recovery, as it's a noop */
 				CheckRestrictedOperation("UNLISTEN");
 				if (stmt->conditionname)
 					Async_Unlisten(stmt->conditionname);
diff --git a/src/test/regress/expected/hs_standby_allowed.out b/src/test/regress/expected/hs_standby_allowed.out
@@ -208,6 +208,9 @@ LOCK hs1 IN ACCESS SHARE MODE;
 LOCK hs1 IN ROW SHARE MODE;
 LOCK hs1 IN ROW EXCLUSIVE MODE;
 COMMIT;
+-- UNLISTEN
+UNLISTEN a;
+UNLISTEN *;
 -- LOAD
 -- should work, easier if there is no test for that...
 -- ALLOWED COMMANDS
diff --git a/src/test/regress/expected/hs_standby_disallowed.out b/src/test/regress/expected/hs_standby_disallowed.out
@@ -118,10 +118,6 @@ listen a;
 ERROR:  cannot execute LISTEN during recovery
 notify a;
 ERROR:  cannot execute NOTIFY during recovery
-unlisten a;
-ERROR:  cannot execute UNLISTEN during recovery
-unlisten *;
-ERROR:  cannot execute UNLISTEN during recovery
 -- disallowed commands
 ANALYZE hs1;
 ERROR:  cannot execute ANALYZE during recovery
diff --git a/src/test/regress/sql/hs_standby_allowed.sql b/src/test/regress/sql/hs_standby_allowed.sql
@@ -110,6 +110,10 @@ LOCK hs1 IN ROW SHARE MODE;
 LOCK hs1 IN ROW EXCLUSIVE MODE;
 COMMIT;
 
+-- UNLISTEN
+UNLISTEN a;
+UNLISTEN *;
+
 -- LOAD
 -- should work, easier if there is no test for that...
 
diff --git a/src/test/regress/sql/hs_standby_disallowed.sql b/src/test/regress/sql/hs_standby_disallowed.sql
@@ -88,8 +88,6 @@ COMMIT;
 -- Listen
 listen a;
 notify a;
-unlisten a;
-unlisten *;
 
 -- disallowed commands
 

Original file line number	Diff line number	Diff line change
`@@ -621,7 +621,7 @@ standard_ProcessUtility(Node *parsetree,`
`621`	`621`	`{`
`622`	`622`	`UnlistenStmt stmt = (UnlistenStmt ) parsetree;`
`623`	`623`
`624`		`- PreventCommandDuringRecovery("UNLISTEN");`
	`624`	`+ /* we allow UNLISTEN during recovery, as it's a noop */`
`625`	`625`	`CheckRestrictedOperation("UNLISTEN");`
`626`	`626`	`if (stmt->conditionname)`
`627`	`627`	`Async_Unlisten(stmt->conditionname);`