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MySQL 5.1 Reference Manual :: 24 APIs and Libraries :: 24.2 MySQL C API :: 24.2.13 Controlling Automatic Reconnect Behavior
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24.2.13. Controlling Automatic Reconnect Behavior

The MySQL client library can perform an automatic reconnect to the server if it finds that the connection is down when you attempt to send a statement to the server to be executed. In this case, the library tries once to reconnect to the server and send the statement again.

Automatic reconnection can be convenient because you need not implement your own reconnect code, but if a reconnection does occur, several aspects of the connection state are reset and your application will not know about it. The connection-related state is affected as follows:

  • Any active transactions are rolled back and autocommit mode is reset.

  • All table locks are released.

  • All TEMPORARY tables are closed (and dropped).

  • Session variables are reinitialized to the values of the corresponding variables. This also affects variables that are set implicitly by statements such as SET NAMES.

  • User variable settings are lost.

  • Prepared statements are released.

  • HANDLER variables are closed.

  • The value of LAST_INSERT_ID() is reset to 0.

  • Locks acquired with GET_LOCK() are released.

  • mysql_ping() does not attempt a reconnection if the connection is down. It returns an error instead.

If it is important for your application to know that the connection has been dropped (so that is can exit or take action to adjust for the loss of state information), be sure to disable auto-reconnect. This can be done explicitly by calling mysql_options() with the MYSQL_OPT_RECONNECT option: 

my_bool reconnect = 0;
mysql_options(&mysql, MYSQL_OPT_RECONNECT, &reconnect);

In MySQL 5.1, auto-reconnect is disabled by default.