MDEV-20699 mysqldump of routines causes MariaDB to get killed by oom-killer

The reason for this behavior is that SP get cached, per connection.
The stored_program_cache is size of this cache, which amounts to 256
routines by default. A compiled stored procedure can easily be several
megabytes in size. Thus calling SHOW CREATE PROCEDURE for all stored
procedures, like mysqldump does, can require significant amount of memory.

Fixed by bypassing the cache for "SHOW CREATE". This should normally be
fine also perfomance-wise, as cache is meant to be used for repeated
execution, not repeated SHOW CREATEs.

Added a test to verify that CREATE PROCEDURE + SHOW CREATE PROCEURE do not
cache, i.e amount of allocated memory does not change.

Note, there is a change in existing behavior in an edge case :
If "SHOW CREATE PROCEDURE p1" called from p1, after p1 was altered, now
this will now return altered code. Previour behavior - relied on caching
and would return old code. The previous behavior might was not necessarily
correct.

mysql-test/main/sp-bugs.result

@@ -182,7 +182,7 @@ RETURN 0;
 END	latin1	latin1_swedish_ci	latin1_swedish_ci
 SHOW CREATE FUNCTION TESTF_bug11763507;
 Function	sql_mode	Create Function	character_set_client	collation_connection	Database Collation
-testf_bug11763507		CREATE DEFINER=`root`@`localhost` FUNCTION `testf_bug11763507`() RETURNS int(11)
+TESTF_bug11763507		CREATE DEFINER=`root`@`localhost` FUNCTION `TESTF_bug11763507`() RETURNS int(11)
 BEGIN
 RETURN 0;
 END	latin1	latin1_swedish_ci	latin1_swedish_ci
@@ -212,7 +212,7 @@ SELECT "PROCEDURE testp_bug11763507";
 END	latin1	latin1_swedish_ci	latin1_swedish_ci
 SHOW CREATE PROCEDURE TESTP_bug11763507;
 Procedure	sql_mode	Create Procedure	character_set_client	collation_connection	Database Collation
-testp_bug11763507		CREATE DEFINER=`root`@`localhost` PROCEDURE `testp_bug11763507`()
+TESTP_bug11763507		CREATE DEFINER=`root`@`localhost` PROCEDURE `TESTP_bug11763507`()
 BEGIN
 SELECT "PROCEDURE testp_bug11763507";
 END	latin1	latin1_swedish_ci	latin1_swedish_ci

mysql-test/main/sp-lock.result

@@ -703,9 +703,6 @@ connection default;
 #
 # SHOW CREATE PROCEDURE p1 called from p1, after p1 was altered
 #
-# We are just covering the existing behaviour with tests. The
-# results are not necessarily correct."
-#
 CREATE PROCEDURE p1()
 BEGIN
 SELECT get_lock("test", 10);
@@ -736,10 +733,7 @@ get_lock("test", 10)
 1
 Procedure	sql_mode	Create Procedure	character_set_client	collation_connection	Database Collation
 p1	STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION	CREATE DEFINER=`root`@`localhost` PROCEDURE `p1`()
-BEGIN
-SELECT get_lock("test", 10);
-SHOW CREATE PROCEDURE p1;
-END	latin1	latin1_swedish_ci	latin1_swedish_ci
+BEGIN END	latin1	latin1_swedish_ci	latin1_swedish_ci
 connection con3;
 disconnect con3;
 connection con2;

mysql-test/main/sp-lock.test

@@ -807,9 +807,6 @@ connection default;
 --echo #
 --echo # SHOW CREATE PROCEDURE p1 called from p1, after p1 was altered
 --echo #
---echo # We are just covering the existing behaviour with tests. The
---echo # results are not necessarily correct."
---echo #
 
 delimiter |;
 CREATE PROCEDURE p1()

mysql-test/main/sp.result

@@ -8893,4 +8893,26 @@ ERROR 42000: You have an error in your SQL syntax; check the manual that corresp
 BEGIN
 RETURN '';
 END' at line 2
+SELECT VARIABLE_VALUE into @global_mem_used FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+SELECT VARIABLE_VALUE into @local_mem_used FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+CREATE PROCEDURE sp0() SELECT 1;
+SHOW CREATE PROCEDURE sp0;
+Procedure	sql_mode	Create Procedure	character_set_client	collation_connection	Database Collation
+sp0	STRICT_ALL_TABLES	CREATE DEFINER=`root`@`localhost` PROCEDURE `sp0`()
+SELECT 1	latin1	latin1_swedish_ci	latin1_swedish_ci
+DROP PROCEDURE sp0;
+SELECT VARIABLE_VALUE into @global_mem_used FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+SELECT VARIABLE_VALUE into @local_mem_used FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+CREATE PROCEDURE sp1() SELECT 1;
+SHOW CREATE PROCEDURE sp1;
+Procedure	sql_mode	Create Procedure	character_set_client	collation_connection	Database Collation
+sp1	STRICT_ALL_TABLES	CREATE DEFINER=`root`@`localhost` PROCEDURE `sp1`()
+SELECT 1	latin1	latin1_swedish_ci	latin1_swedish_ci
+SELECT VARIABLE_VALUE-@local_mem_used FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+VARIABLE_VALUE-@local_mem_used
+0
+SELECT VARIABLE_VALUE-@global_mem_used FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+VARIABLE_VALUE-@global_mem_used
+0
+DROP PROCEDURE sp1;
 # End of 10.3 tests

mysql-test/main/sp.test

@@ -10431,4 +10431,21 @@ END;
 $$
 DELIMITER ;$$
 
+# MDEV-20699 do not cache SP in SHOW CREATE
+# Warmup round, this might allocate some memory for session variable
+# and the output
+SELECT VARIABLE_VALUE into @global_mem_used FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+SELECT VARIABLE_VALUE into @local_mem_used FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+CREATE PROCEDURE sp0() SELECT 1;
+SHOW CREATE PROCEDURE sp0;
+DROP PROCEDURE sp0;
+
+#Check that CREATE/SHOW does not use memory in caches.
+SELECT VARIABLE_VALUE into @global_mem_used FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+SELECT VARIABLE_VALUE into @local_mem_used FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+CREATE PROCEDURE sp1() SELECT 1;
+SHOW CREATE PROCEDURE sp1;
+SELECT VARIABLE_VALUE-@local_mem_used FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+SELECT VARIABLE_VALUE-@global_mem_used FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME='MEMORY_USED';
+DROP PROCEDURE sp1;
 --echo # End of 10.3 tests

sql/sp.cc

@@ -1890,8 +1890,6 @@ bool
 Sp_handler::sp_show_create_routine(THD *thd,
                                    const Database_qualified_name *name) const
 {
-  sp_head *sp;
-
   DBUG_ENTER("sp_show_create_routine");
   DBUG_PRINT("enter", ("type: %s name: %.*s",
                        type_str(),
@@ -1904,20 +1902,20 @@ Sp_handler::sp_show_create_routine(THD *thd,
     It is "safe" to do as long as it doesn't affect the results
     of the binary log or the query cache, which currently it does not.
   */
-  if (sp_cache_routine(thd, name, false, &sp))
-    DBUG_RETURN(TRUE);
-
-  if (sp == NULL || sp->show_create_routine(thd, this))
+  sp_head *sp= 0;
+  bool free_sp= db_find_routine(thd, name, &sp) == SP_OK;
+  bool ret= !sp || sp->show_create_routine(thd, this);
+  if (ret)
   {
     /*
       If we have insufficient privileges, pretend the routine
       does not exist.
     */
     my_error(ER_SP_DOES_NOT_EXIST, MYF(0), type_str(), name->m_name.str);
-    DBUG_RETURN(TRUE);
   }
-
-  DBUG_RETURN(FALSE);
+  if (free_sp)
+    sp_head::destroy(sp);
+  DBUG_RETURN(ret);
 }