Synchronous connectors can rely on OK_Packet/EOF_Packet server status's SERVER_STATUS_IN_TRANS flag that explicitly indicate if a transaction is currently active.
Java connector use that information to avoid issuing a rollback/commit command, skipping the command if there is no transaction.
Problem concerns only MyISAM that never set SERVER_STATUS_IN_TRANS flag. Still there is some case when there is some kind of lock : ( example from serg: )
and in another
this DROP TABLE will wait until the transaction ends.
- either MyISAM should return SERVER_STATUS_IN_TRANS flag, so connector know there is really a commit to be issued.
- either MyISAM doesn't set any lock. (It may be just an issue : for some metadata locks are taken on the object name, before the table is opened, before we know it's a MyISAM table.)
Either way is ok.
(Another solution would be to always issue a COMMIT/ROLLBACK statement when there is no need, but that would degrade performance dramatically for some application. For example when connections are given back to pools, pools generally issues a connection.rollback() to ensure connection state, and there is lots of application where that command would represent 25% of the commands)