Description:
Reference:
http://dev.mysql.com/doc/refman/5.6/en/lock-tables.html
"A table lock only protects against inappropriate reads or writes by other sessions. A session holding a WRITE lock can perform table-level operations such as DROP TABLE or TRUNCATE TABLE. For sessions holding a READ lock, DROP TABLE and TRUNCATE TABLE operations are not permitted. *TRUNCATE TABLE operations are not transaction-safe, so an error occurs if the session attempts one during an active transaction or while holding a READ lock.*"
While it is true an error will occur if you hold a READ lock. It is not true that an error occurs if one is attempted during an active transaction. As referenced here:
http://dev.mysql.com/doc/refman/5.6/en/implicit-commit.html
How to repeat:
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
| 0 |
+--------------+
1 row in set (0.00 sec)
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
mysql> truncate table t1;
Query OK, 0 rows affected (0.47 sec)
mysql> LOCK TABLES t1 READ;
Query OK, 0 rows affected (0.00 sec)
mysql> truncate table t1;
ERROR 1099 (HY000): Table 't1' was locked with a READ lock and can't be updated
mysql> UNLOCK TABLES;
Query OK, 0 rows affected (0.00 sec)
mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t1 values();
Query OK, 1 row affected (0.01 sec)
mysql> insert into t1 values();
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)
mysql> truncate table t1;
Query OK, 0 rows affected (0.71 sec)
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t1;
Empty set (0.00 sec)
Suggested fix:
Remove line:
"*TRUNCATE TABLE operations are not transaction-safe, so an error occurs if the session attempts one during an active transaction or while holding a READ lock.*"
The part about READ lock not allowed is mentioned in the previous sentence.
"For sessions holding a READ lock, DROP TABLE and TRUNCATE TABLE operations are not permitted."
