Fix bug #11946, truncate not always resetting the auto-increment counter

in InnoDB tables.

mysql-test/r/innodb.result

@@ -2483,3 +2483,26 @@ delete t1 from t1,t2 where f1=f3 and f4='cc';
 select * from t1;
 f1	f2
 drop table t1,t2;
+CREATE TABLE t1 (
+id INTEGER NOT NULL AUTO_INCREMENT, PRIMARY KEY (id)
+) ENGINE=InnoDB;
+CREATE TABLE t2 (
+id INTEGER NOT NULL,
+FOREIGN KEY (id) REFERENCES t1 (id)
+) ENGINE=InnoDB;
+INSERT INTO t1 (id) VALUES (NULL);
+SELECT * FROM t1;
+id
+1
+TRUNCATE t1;
+INSERT INTO t1 (id) VALUES (NULL);
+SELECT * FROM t1;
+id
+1
+DELETE FROM t1;
+TRUNCATE t1;
+INSERT INTO t1 (id) VALUES (NULL);
+SELECT * FROM t1;
+id
+1
+DROP TABLE t2, t1;

mysql-test/t/innodb.test

@@ -1404,3 +1404,31 @@ insert into t1 values ('aa','bb'),('aa','cc');
 delete t1 from t1,t2 where f1=f3 and f4='cc';
 select * from t1;
 drop table t1,t2;
+
+#
+# Test that the slow TRUNCATE implementation resets autoincrement columns
+# (bug #11946)
+#
+
+CREATE TABLE t1 (
+id INTEGER NOT NULL AUTO_INCREMENT, PRIMARY KEY (id)
+) ENGINE=InnoDB;
+
+CREATE TABLE t2 (
+id INTEGER NOT NULL,
+FOREIGN KEY (id) REFERENCES t1 (id)
+) ENGINE=InnoDB;
+
+INSERT INTO t1 (id) VALUES (NULL);
+SELECT * FROM t1;
+TRUNCATE t1;
+INSERT INTO t1 (id) VALUES (NULL);
+SELECT * FROM t1;
+
+# continued from above; test that doing a slow TRUNCATE on a table with 0
+# rows resets autoincrement columns
+DELETE FROM t1;
+TRUNCATE t1;
+INSERT INTO t1 (id) VALUES (NULL);
+SELECT * FROM t1;
+DROP TABLE t2, t1;

sql/ha_innodb.cc

@@ -6782,6 +6782,28 @@ ha_innobase::get_auto_increment()
 	return((ulonglong) nr);
 }
 
+/* See comment in handler.h */
+int
+ha_innobase::reset_auto_increment()
+{
+	DBUG_ENTER("ha_innobase::reset_auto_increment");
+
+	row_prebuilt_t* prebuilt = (row_prebuilt_t*) innobase_prebuilt;
+  	int     	error;
+
+	error = row_lock_table_autoinc_for_mysql(prebuilt);
+
+	if (error != DB_SUCCESS) {
+		error = convert_error_code_to_mysql(error, user_thd);
+
+		DBUG_RETURN(error);
+	}	
+
+	dict_table_autoinc_initialize(prebuilt->table, 0);
+
+	DBUG_RETURN(0);
+}
+
 /***********************************************************************
 Compares two 'refs'. A 'ref' is the (internal) primary key value of the row.
 If there is no explicitly declared non-null unique key or a primary key, then

sql/ha_innodb.h

@@ -173,6 +173,8 @@ class ha_innobase: public handler
 			     		enum thr_lock_type lock_type);
 	void init_table_handle_for_HANDLER(); 
 	ulonglong get_auto_increment();
+	int reset_auto_increment();
+	
         uint8 table_cache_type() { return HA_CACHE_TBL_ASKTRANSACT; }
         /*
           ask handler about permission to cache table during query registration

sql/handler.h

@@ -650,6 +650,15 @@ public:
   { return (my_errno=HA_ERR_WRONG_COMMAND); }
   virtual ulonglong get_auto_increment();
   virtual void restore_auto_increment();
+
+  /* This is called after TRUNCATE is emulated by doing a 'DELETE FROM t',
+     in which case we need a separate operation for resetting the table's
+     auto-increment counter. HA_ERR_WRONG_COMMAND is returned by storage
+     engines that have no need for this, i.e. those that can always do a
+     fast TRUNCATE. */
+  virtual int reset_auto_increment()
+  { return HA_ERR_WRONG_COMMAND; }
+
   virtual void update_create_info(HA_CREATE_INFO *create_info) {}
 
   /* admin commands - called from mysql_admin_table */

sql/sql_delete.cc

@@ -103,6 +103,13 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
     free_underlaid_joins(thd, select_lex);
     thd->row_count_func= 0;
     send_ok(thd,0L);
+
+    /*
+      We don't need to call reset_auto_increment in this case, because
+      mysql_truncate always gives a NULL conds argument, hence we never
+      get here.
+    */
+
     DBUG_RETURN(0);				// Nothing to delete
   }
 
@@ -226,6 +233,21 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   if (options & OPTION_QUICK)
     (void) table->file->extra(HA_EXTRA_NORMAL);
 
+  if ((error < 0) && (thd->lex->sql_command == SQLCOM_TRUNCATE))
+  {
+    /*
+      We're really doing a truncate and need to reset the table's
+      auto-increment counter.
+    */
+    int error2 = table->file->reset_auto_increment();
+
+    if (error2 && (error2 != HA_ERR_WRONG_COMMAND))
+    {
+      table->file->print_error(error2, MYF(0));
+      error = 1;
+    }
+  }
+
 cleanup:
   /*
     Invalidate the table in the query cache if something changed. This must