+1 =)

mysql manual sometimes don't help, that's why i really prefer mariadb kb

i think that many years ago mysql implement this nontransactional like locks to innodb just to allow guys porting from myisam to innodb using old apps without rewriting the lock/unlock to begin/commit

if you are using innodb as transactional you will never use lock/unlock, in my opnion maybe you probably only use locks at filesystem or use get_lock() mysql function or any other IPC function, but be carefull about scalability i don't know what's the 'best' lock server today, all shared locks that i use today i use over a filesystem and network (nfs/smb/others network file system), if get_lock work with galera maybe i could get a try

2014-09-23 6:51 GMT-03:00 Elena Stepanova <elenst@montyprogram.com>:

Hi Federico,

On 23.09.2014 12:50, Federico Razzoli wrote:

Let's make the snippet simpler. Only one table, non-transactional, please look at the difference from what docs say and the real behaviour. If one could explain what UNLOCK TABLES exactly does, it would be great.

MariaDB [test]> SELECT @@in_transaction, @@autocommit;
+------------------+--------------+
| @@in_transaction | @@autocommit |
+------------------+--------------+
| 0 | 1 |
+------------------+--------------+
1 row in set (0.00 sec)

MariaDB [test]> CREATE OR REPLACE TABLE t (c INT) ENGINE = MEMORY;
Query OK, 0 rows affected (0.12 sec)

MariaDB [test]> LOCK TABLE t WRITE;
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)

"Beginning a transaction causes table locks acquired with LOCK TABLES to be released, as though you had executed UNLOCK TABLES."

http://dev.mysql.com/doc/refman/5.5/en/commit.html

MariaDB [test]> INSERT INTO t VALUES (1);
Query OK, 1 row affected (0.01 sec)

MariaDB [test]> UNLOCK TABLES;
Query OK, 0 rows affected (0.00 sec)

So, this UNLOCK is not actually doing anything.

Regards,
Elena

MariaDB [test]> SELECT @@in_transaction;
+------------------+
| @@in_transaction |
+------------------+
| 1 |
+------------------+
1 row in set (0.00 sec)

Regards
Federico

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Eng. Automação e Controle