Bug #26242 UPDATE with subquery and triggers failing with cluster tables

In certain cases AFTER UPDATE/DELETE triggers on NDB tables that referenced
subject table didn't see the results of operation which caused invocation
of those triggers. In other words AFTER trigger invoked as result of update
(or deletion) of particular row saw version of this row before update (or
deletion).

The problem occured because NDB handler in those cases postponed actual
update/delete operations to be able to perform them later as one batch.

This fix solves the problem by disabling this optimization for particular
operation if subject table has AFTER trigger for this operation defined.
To achieve this we introduce two new flags for handler::extra() method:
HA_EXTRA_DELETE_CANNOT_BATCH and HA_EXTRA_UPDATE_CANNOT_BATCH.
These are called if there exists AFTER DELETE/UPDATE triggers during a
statement that potentially can generate calls to delete_row()/update_row().
This includes multi_delete/multi_update statements as well as insert statements
that do delete/update as part of an ON DUPLICATE statement.


include/my_base.h:
  Added HA_EXTRA_DELETE_CANNOT_BATCH and HA_EXTRA_UPDATE_CANNOT_BATCH to inform handler when batching of delete/update is not possible.
mysql-test/r/ndb_trigger.result:
  Bug #26242  UPDATE with subquery and triggers failing with cluster tables
  ---
  Added new test cases
mysql-test/t/ndb_trigger.test:
  Bug #26242  UPDATE with subquery and triggers failing with cluster tables
  ---
  Added new test cases
sql/ha_ndbcluster.cc:
  Bug #26242  UPDATE with subquery and triggers failing with cluster tables: Use HA_EXTRA_DELETE_CANNOT_BATCH and HA_EXTRA_UPDATE_CANNOT_BATCH to inform handler when batching of delete/update is not possible
sql/ha_ndbcluster.h:
  Bug #26242  UPDATE with subquery and triggers failing with cluster tables: Added member variables for handling of HA_EXTRA_DELETE_CANNOT_BATCH and HA_EXTRA_UPDATE_CANNOT_BATCH to inform handler when batching of delete/update is not possible
sql/mysql_priv.h:
  Added new method prepare_triggers_for_insert_stmt to check if batching of delete/update must be disallowed.
sql/sql_delete.cc:
  Use HA_EXTRA_DELETE_CANNOT_BATCH to inform handler when batching of delete is not possible
sql/sql_insert.cc:
  Added method prepare_triggers_for_insert_stmt to check if batching of delete/update must be dissallowed.
  Use HA_EXTRA_DELETE_CANNOT_BATCH and HA_EXTRA_UPDATE_CANNOT_BATCH to inform handler
   when batching of delete/update is not possible
sql/sql_load.cc:
  Call prepare_triggers_for_insert_stmt to check if batching of delete/update must be dissallowed and
  mark fields used by triggers for the insert statement.
sql/sql_trigger.h:
  Added has_triggers to support what particular triggers exist on a table.
sql/sql_update.cc:
  Use HA_EXTRA_UPDATE_CANNOT_BATCH to inform handler when batching of update is not possible

include/my_base.h

@@ -161,7 +161,15 @@ enum ha_extra_function {
     Off by default.
   */
   HA_EXTRA_WRITE_CAN_REPLACE,
-  HA_EXTRA_WRITE_CANNOT_REPLACE
+  HA_EXTRA_WRITE_CANNOT_REPLACE,
+  /*
+    Inform handler that delete_row()/update_row() cannot batch deletes/updates
+    and should perform them immediately. This may be needed when table has 
+    AFTER DELETE/UPDATE triggers which access to subject table.
+    These flags are reset by the handler::extra(HA_EXTRA_RESET) call.
+  */
+  HA_EXTRA_DELETE_CANNOT_BATCH,
+  HA_EXTRA_UPDATE_CANNOT_BATCH
 };
 
 	/* The following is parameter to ha_panic() */

mysql-test/r/ndb_trigger.result

@@ -116,4 +116,175 @@ op	a	b
 d	1	1.050000000000000000000000000000
 d	2	2.050000000000000000000000000000
 drop tables t1, t2, t3;
+CREATE TABLE t1 (
+id INT NOT NULL PRIMARY KEY,
+xy INT
+) ENGINE=ndbcluster;
+INSERT INTO t1 VALUES (1, 0);
+CREATE TRIGGER t1_update AFTER UPDATE ON t1 FOR EACH ROW BEGIN REPLACE INTO t2 SELECT * FROM t1 WHERE t1.id = NEW.id; END //
+CREATE TABLE t2 (
+id INT NOT NULL PRIMARY KEY,
+xy INT
+) ENGINE=ndbcluster;
+INSERT INTO t2 VALUES (2, 0);
+CREATE TABLE t3 (id INT NOT NULL PRIMARY KEY) ENGINE=ndbcluster;
+INSERT INTO t3 VALUES (1);
+CREATE TABLE t4 LIKE t1;
+CREATE TRIGGER t4_update AFTER UPDATE ON t4 FOR EACH ROW BEGIN REPLACE INTO t5 SELECT * FROM t4 WHERE t4.id = NEW.id; END //
+CREATE TABLE t5 LIKE t2;
+UPDATE t1 SET xy = 3 WHERE id = 1;
+SELECT xy FROM t1 where id = 1;
+xy
+3
+SELECT xy FROM t2 where id = 1;
+xy
+3
+UPDATE t1 SET xy  = 4 WHERE id IN (SELECT id FROM t3 WHERE id = 1);
+SELECT xy FROM t1 where id = 1;
+xy
+4
+SELECT xy FROM t2 where id = 1;
+xy
+4
+INSERT INTO t4 SELECT * FROM t1;
+INSERT INTO t5 SELECT * FROM t2;
+UPDATE t1,t4 SET t1.xy = 3, t4.xy = 3 WHERE t1.id = 1 AND t4.id = 1;
+SELECT xy FROM t1 where id = 1;
+xy
+3
+SELECT xy FROM t2 where id = 1;
+xy
+3
+SELECT xy FROM t4 where id = 1;
+xy
+3
+SELECT xy FROM t5 where id = 1;
+xy
+3
+UPDATE t1,t4 SET t1.xy = 4, t4.xy = 4 WHERE t1.id IN (SELECT id FROM t3 WHERE id = 1) AND t4.id IN (SELECT id FROM t3 WHERE id = 1);
+SELECT xy FROM t1 where id = 1;
+xy
+4
+SELECT xy FROM t2 where id = 1;
+xy
+4
+SELECT xy FROM t4 where id = 1;
+xy
+4
+SELECT xy FROM t5 where id = 1;
+xy
+4
+INSERT INTO t1 VALUES (1,0) ON DUPLICATE KEY UPDATE xy = 5;
+SELECT xy FROM t1 where id = 1;
+xy
+5
+SELECT xy FROM t2 where id = 1;
+xy
+5
+DROP TRIGGER t1_update;
+DROP TRIGGER t4_update;
+CREATE TRIGGER t1_delete AFTER DELETE ON t1 FOR EACH ROW BEGIN REPLACE INTO t2 SELECT * FROM t1 WHERE t1.id > 4; END //
+CREATE TRIGGER t4_delete AFTER DELETE ON t4 FOR EACH ROW BEGIN REPLACE INTO t5 SELECT * FROM t4 WHERE t4.id > 4; END //
+INSERT INTO t1 VALUES (5, 0),(6,0);
+INSERT INTO t2 VALUES (5, 1),(6,1);
+INSERT INTO t3 VALUES (5);
+SELECT * FROM t1 order by id;
+id	xy
+1	5
+5	0
+6	0
+SELECT * FROM t2 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	1
+DELETE FROM t1 WHERE id IN (SELECT id FROM t3 WHERE id = 5);
+SELECT * FROM t1 order by id;
+id	xy
+1	5
+6	0
+SELECT * FROM t2 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	0
+INSERT INTO t1 VALUES (5,0);
+UPDATE t2 SET xy = 1 WHERE id = 6;
+TRUNCATE t4;
+INSERT INTO t4 SELECT * FROM t1;
+TRUNCATE t5;
+INSERT INTO t5 SELECT * FROM t2;
+SELECT * FROM t1 order by id;
+id	xy
+1	5
+5	0
+6	0
+SELECT * FROM t2 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	1
+SELECT * FROM t4 order by id;
+id	xy
+1	5
+5	0
+6	0
+SELECT * FROM t5 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	1
+DELETE FROM t1,t4 USING t1,t3,t4 WHERE t1.id IN (SELECT id FROM t3 WHERE id = 5) AND t4.id IN (SELECT id FROM t3 WHERE id = 5);
+SELECT * FROM t1 order by id;
+id	xy
+1	5
+6	0
+SELECT * FROM t2 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	0
+SELECT * FROM t4 order by id;
+id	xy
+1	5
+6	0
+SELECT * FROM t5 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	0
+INSERT INTO t1 VALUES (5, 0);
+REPLACE INTO t2 VALUES (6,1);
+SELECT * FROM t1 order by id;
+id	xy
+1	5
+5	0
+6	0
+SELECT * FROM t2 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	1
+REPLACE INTO t1 VALUES (5, 1);
+SELECT * FROM t1 order by id;
+id	xy
+1	5
+5	1
+6	0
+SELECT * FROM t2 order by id;
+id	xy
+1	5
+2	0
+5	1
+6	0
+DROP TRIGGER t1_delete;
+DROP TRIGGER t4_delete;
+DROP TABLE t1, t2, t3, t4, t5;
 End of 5.0 tests

mysql-test/t/ndb_trigger.test

@@ -89,4 +89,112 @@ select * from t2 order by op, a, b;
 
 drop tables t1, t2, t3;
 
+# Test for bug#26242
+# Verify that AFTER UPDATE/DELETE triggers are executed
+# after the change has actually taken place
+
+CREATE TABLE t1 (
+  id INT NOT NULL PRIMARY KEY,
+  xy INT
+) ENGINE=ndbcluster;
+
+INSERT INTO t1 VALUES (1, 0);
+
+DELIMITER //;
+CREATE TRIGGER t1_update AFTER UPDATE ON t1 FOR EACH ROW BEGIN REPLACE INTO t2 SELECT * FROM t1 WHERE t1.id = NEW.id; END //
+DELIMITER ;//
+
+CREATE TABLE t2 (
+  id INT NOT NULL PRIMARY KEY,
+  xy INT
+) ENGINE=ndbcluster;
+
+INSERT INTO t2 VALUES (2, 0);
+
+CREATE TABLE t3 (id INT NOT NULL PRIMARY KEY) ENGINE=ndbcluster;
+
+INSERT INTO t3 VALUES (1);
+
+CREATE TABLE t4 LIKE t1;
+
+DELIMITER //;
+CREATE TRIGGER t4_update AFTER UPDATE ON t4 FOR EACH ROW BEGIN REPLACE INTO t5 SELECT * FROM t4 WHERE t4.id = NEW.id; END //
+DELIMITER ;//
+
+CREATE TABLE t5 LIKE t2;
+
+UPDATE t1 SET xy = 3 WHERE id = 1;
+SELECT xy FROM t1 where id = 1;
+SELECT xy FROM t2 where id = 1;
+
+UPDATE t1 SET xy  = 4 WHERE id IN (SELECT id FROM t3 WHERE id = 1);
+SELECT xy FROM t1 where id = 1;
+SELECT xy FROM t2 where id = 1;
+
+INSERT INTO t4 SELECT * FROM t1;
+INSERT INTO t5 SELECT * FROM t2;
+UPDATE t1,t4 SET t1.xy = 3, t4.xy = 3 WHERE t1.id = 1 AND t4.id = 1;
+SELECT xy FROM t1 where id = 1;
+SELECT xy FROM t2 where id = 1;
+SELECT xy FROM t4 where id = 1;
+SELECT xy FROM t5 where id = 1;
+
+UPDATE t1,t4 SET t1.xy = 4, t4.xy = 4 WHERE t1.id IN (SELECT id FROM t3 WHERE id = 1) AND t4.id IN (SELECT id FROM t3 WHERE id = 1);
+SELECT xy FROM t1 where id = 1;
+SELECT xy FROM t2 where id = 1;
+SELECT xy FROM t4 where id = 1;
+SELECT xy FROM t5 where id = 1;
+
+INSERT INTO t1 VALUES (1,0) ON DUPLICATE KEY UPDATE xy = 5;
+SELECT xy FROM t1 where id = 1;
+SELECT xy FROM t2 where id = 1;
+
+DROP TRIGGER t1_update;
+DROP TRIGGER t4_update;
+
+DELIMITER //;
+CREATE TRIGGER t1_delete AFTER DELETE ON t1 FOR EACH ROW BEGIN REPLACE INTO t2 SELECT * FROM t1 WHERE t1.id > 4; END //
+DELIMITER ;//
+
+DELIMITER //;
+CREATE TRIGGER t4_delete AFTER DELETE ON t4 FOR EACH ROW BEGIN REPLACE INTO t5 SELECT * FROM t4 WHERE t4.id > 4; END //
+DELIMITER ;//
+
+INSERT INTO t1 VALUES (5, 0),(6,0);
+INSERT INTO t2 VALUES (5, 1),(6,1);
+INSERT INTO t3 VALUES (5);
+SELECT * FROM t1 order by id;
+SELECT * FROM t2 order by id;
+DELETE FROM t1 WHERE id IN (SELECT id FROM t3 WHERE id = 5);
+SELECT * FROM t1 order by id;
+SELECT * FROM t2 order by id;
+
+INSERT INTO t1 VALUES (5,0);
+UPDATE t2 SET xy = 1 WHERE id = 6;
+TRUNCATE t4;
+INSERT INTO t4 SELECT * FROM t1;
+TRUNCATE t5;
+INSERT INTO t5 SELECT * FROM t2;
+SELECT * FROM t1 order by id;
+SELECT * FROM t2 order by id;
+SELECT * FROM t4 order by id;
+SELECT * FROM t5 order by id;
+DELETE FROM t1,t4 USING t1,t3,t4 WHERE t1.id IN (SELECT id FROM t3 WHERE id = 5) AND t4.id IN (SELECT id FROM t3 WHERE id = 5);
+SELECT * FROM t1 order by id;
+SELECT * FROM t2 order by id;
+SELECT * FROM t4 order by id;
+SELECT * FROM t5 order by id;
+
+INSERT INTO t1 VALUES (5, 0);
+REPLACE INTO t2 VALUES (6,1);
+SELECT * FROM t1 order by id;
+SELECT * FROM t2 order by id;
+REPLACE INTO t1 VALUES (5, 1);
+SELECT * FROM t1 order by id;
+SELECT * FROM t2 order by id;
+
+DROP TRIGGER t1_delete;
+DROP TRIGGER t4_delete;
+DROP TABLE t1, t2, t3, t4, t5;
+
 --echo End of 5.0 tests

sql/ha_ndbcluster.cc

@@ -2524,8 +2524,13 @@ int ha_ndbcluster::update_row(const byte *old_data, byte *new_data)
       ERR_RETURN(op->getNdbError());
   }
 
-  // Execute update operation
-  if (!cursor && execute_no_commit(this,trans,false) != 0) {
+  /*
+    Execute update operation if we are not doing a scan for update
+    and there exist UPDATE AFTER triggers
+  */
+
+  if ((!cursor || m_update_cannot_batch) && 
+      execute_no_commit(this,trans,false) != 0) {
     no_uncommitted_rows_execute_failure();
     DBUG_RETURN(ndb_err(trans));
   }
@@ -2566,7 +2571,7 @@ int ha_ndbcluster::delete_row(const byte *record)
 
     no_uncommitted_rows_update(-1);
 
-    if (!m_primary_key_update)
+    if (!(m_primary_key_update || m_delete_cannot_batch))
       // If deleting from cursor, NoCommit will be handled in next_result
       DBUG_RETURN(0);
   }
@@ -3277,6 +3282,8 @@ int ha_ndbcluster::extra(enum ha_extra_function operation)
     DBUG_PRINT("info", ("HA_EXTRA_RESET"));
     DBUG_PRINT("info", ("Clearing condition stack"));
     cond_clear();
+    m_delete_cannot_batch= FALSE;
+    m_update_cannot_batch= FALSE;
     break;
   case HA_EXTRA_CACHE:                 /* Cash record in HA_rrnd() */
     DBUG_PRINT("info", ("HA_EXTRA_CACHE"));
@@ -3393,6 +3400,14 @@ int ha_ndbcluster::extra(enum ha_extra_function operation)
     DBUG_PRINT("info", ("Turning OFF use of write instead of insert"));
     m_use_write= FALSE;
     break;
+  case HA_EXTRA_DELETE_CANNOT_BATCH:
+    DBUG_PRINT("info", ("HA_EXTRA_DELETE_CANNOT_BATCH"));
+    m_delete_cannot_batch= TRUE;
+    break;
+  case HA_EXTRA_UPDATE_CANNOT_BATCH:
+    DBUG_PRINT("info", ("HA_EXTRA_UPDATE_CANNOT_BATCH"));
+    m_update_cannot_batch= TRUE;
+    break;
   }
   
   DBUG_RETURN(0);
@@ -4744,6 +4759,8 @@ ha_ndbcluster::ha_ndbcluster(TABLE *table_arg):
   m_bulk_insert_rows((ha_rows) 1024),
   m_rows_changed((ha_rows) 0),
   m_bulk_insert_not_flushed(FALSE),
+  m_delete_cannot_batch(FALSE),
+  m_update_cannot_batch(FALSE),
   m_ops_pending(0),
   m_skip_auto_increment(TRUE),
   m_blobs_pending(0),

sql/ha_ndbcluster.h

@@ -774,6 +774,8 @@ bool uses_blob_value(bool all_fields);
   ha_rows m_bulk_insert_rows;
   ha_rows m_rows_changed;
   bool m_bulk_insert_not_flushed;
+  bool m_delete_cannot_batch;
+  bool m_update_cannot_batch;
   ha_rows m_ops_pending;
   bool m_skip_auto_increment;
   bool m_blobs_pending;

sql/mysql_priv.h

@@ -811,6 +811,8 @@ bool mysql_insert(THD *thd,TABLE_LIST *table,List<Item> &fields,
                   bool ignore);
 int check_that_all_fields_are_given_values(THD *thd, TABLE *entry,
                                            TABLE_LIST *table_list);
+void prepare_triggers_for_insert_stmt(THD *thd, TABLE *table,
+                                      enum_duplicates duplic);
 void mark_fields_used_by_triggers_for_insert_stmt(THD *thd, TABLE *table,
                                                   enum_duplicates duplic);
 bool mysql_prepare_delete(THD *thd, TABLE_LIST *table_list, Item **conds);

sql/sql_delete.cc

@@ -209,7 +209,19 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   thd->proc_info="updating";
 
   if (table->triggers)
+  {
     table->triggers->mark_fields_used(thd, TRG_EVENT_DELETE);
+    if (table->triggers->has_triggers(TRG_EVENT_DELETE,
+                                      TRG_ACTION_AFTER))
+    {
+      /*
+	The table has AFTER DELETE triggers that might access to subject table
+	and therefore might need delete to be done immediately. So we turn-off
+	the batching.
+      */
+      (void) table->file->extra(HA_EXTRA_DELETE_CANNOT_BATCH);
+    }
+  }
 
   while (!(error=info.read_record(&info)) && !thd->killed &&
 	 !thd->net.report_error)
@@ -526,7 +538,19 @@ multi_delete::initialize_tables(JOIN *join)
       else
 	normal_tables= 1;
       if (tbl->triggers)
+      {
         tbl->triggers->mark_fields_used(thd, TRG_EVENT_DELETE);
+	if (tbl->triggers->has_triggers(TRG_EVENT_DELETE,
+                                      TRG_ACTION_AFTER))
+	{
+	  /*
+	    The table has AFTER DELETE triggers that might access to subject 
+	    table and therefore might need delete to be done immediately. 
+	    So we turn-off the batching.
+	  */
+	  (void) tbl->file->extra(HA_EXTRA_DELETE_CANNOT_BATCH);
+	}
+      }
     }
     else if ((tab->type != JT_SYSTEM && tab->type != JT_CONST) &&
              walk == delete_tables)

sql/sql_insert.cc

@@ -279,6 +279,51 @@ static int check_update_fields(THD *thd, TABLE_LIST *insert_table_list,
 }
 
 
+/*
+  Prepare triggers  for INSERT-like statement.
+
+  SYNOPSIS
+    prepare_triggers_for_insert_stmt()
+      thd     The current thread
+      table   Table to which insert will happen
+      duplic  Type of duplicate handling for insert which will happen
+
+  NOTE
+    Prepare triggers for INSERT-like statement by marking fields
+    used by triggers and inform handlers that batching of UPDATE/DELETE 
+    cannot be done if there are BEFORE UPDATE/DELETE triggers.
+*/
+
+void prepare_triggers_for_insert_stmt(THD *thd, TABLE *table,
+                                      enum_duplicates duplic)
+{
+  if (table->triggers)
+  {
+    if (table->triggers->has_triggers(TRG_EVENT_DELETE,
+                                      TRG_ACTION_AFTER))
+    {
+      /*
+        The table has AFTER DELETE triggers that might access to 
+        subject table and therefore might need delete to be done 
+        immediately. So we turn-off the batching.
+      */ 
+      (void) table->file->extra(HA_EXTRA_DELETE_CANNOT_BATCH);
+    }
+    if (table->triggers->has_triggers(TRG_EVENT_UPDATE,
+                                      TRG_ACTION_AFTER))
+    {
+      /*
+        The table has AFTER UPDATE triggers that might access to subject 
+        table and therefore might need update to be done immediately. 
+        So we turn-off the batching.
+      */ 
+      (void) table->file->extra(HA_EXTRA_UPDATE_CANNOT_BATCH);
+    }
+    mark_fields_used_by_triggers_for_insert_stmt(thd, table, duplic);
+  }
+}
+
+
 /*
   Mark fields used by triggers for INSERT-like statement.
 
@@ -513,7 +558,7 @@ bool mysql_insert(THD *thd,TABLE_LIST *table_list,
     error= 1;
   }
 
-  mark_fields_used_by_triggers_for_insert_stmt(thd, table, duplic);
+  prepare_triggers_for_insert_stmt(thd, table, duplic);
 
   if (table_list->prepare_where(thd, 0, TRUE) ||
       table_list->prepare_check_option(thd))
@@ -2393,8 +2438,8 @@ select_insert::prepare(List<Item> &values, SELECT_LEX_UNIT *u)
         table_list->prepare_check_option(thd));
 
   if (!res)
-    mark_fields_used_by_triggers_for_insert_stmt(thd, table,
-                                                 info.handle_duplicates);
+    prepare_triggers_for_insert_stmt(thd, table,
+                                     info.handle_duplicates);
   DBUG_RETURN(res);
 }
 

sql/sql_load.cc

@@ -222,7 +222,7 @@ bool mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list,
       DBUG_RETURN(TRUE);
   }
 
-  mark_fields_used_by_triggers_for_insert_stmt(thd, table, handle_duplicates);
+  prepare_triggers_for_insert_stmt(thd, table, handle_duplicates);
 
   uint tot_length=0;
   bool use_blobs= 0, use_vars= 0;

sql/sql_trigger.h

@@ -110,6 +110,11 @@ public:
                                 const char *old_table,
                                 const char *new_db,
                                 const char *new_table);
+  bool has_triggers(trg_event_type event_type, 
+                    trg_action_time_type action_time)
+  {
+    return (bodies[event_type][action_time]);
+  }
   bool has_delete_triggers()
   {
     return (bodies[TRG_EVENT_DELETE][TRG_ACTION_BEFORE] ||

sql/sql_update.cc

@@ -435,7 +435,19 @@ int mysql_update(THD *thd,
                                 MODE_STRICT_ALL_TABLES)));
 
   if (table->triggers)
+  {
     table->triggers->mark_fields_used(thd, TRG_EVENT_UPDATE);
+    if (table->triggers->has_triggers(TRG_EVENT_UPDATE,
+                                      TRG_ACTION_AFTER))
+    {
+      /*
+	The table has AFTER UPDATE triggers that might access to subject 
+	table and therefore might need update to be done immediately. 
+	So we turn-off the batching.
+      */ 
+      (void) table->file->extra(HA_EXTRA_UPDATE_CANNOT_BATCH);
+    }
+  }
 
   /*
     We can use compare_record() to optimize away updates if
@@ -1000,6 +1012,20 @@ int multi_update::prepare(List<Item> &not_used_values,
       table->no_keyread=1;
       table->used_keys.clear_all();
       table->pos_in_table_list= tl;
+      if (table->triggers)
+      {
+	table->triggers->mark_fields_used(thd, TRG_EVENT_UPDATE);
+	if (table->triggers->has_triggers(TRG_EVENT_UPDATE,
+					  TRG_ACTION_AFTER))
+	{
+	  /*
+	    The table has AFTER UPDATE triggers that might access to subject 
+	    table and therefore might need update to be done immediately. 
+	    So we turn-off the batching.
+	  */ 
+	  (void) table->file->extra(HA_EXTRA_UPDATE_CANNOT_BATCH);
+	}
+      }
     }
   }