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20.6.15 Controlling Automatic Reconnection Behavior

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

If it is important for your application to know that the connection has been dropped (so that it can exit or take action to adjust for the loss of state information), be sure that auto-reconnect is disabled. To ensure this, call mysql_options() with the MYSQL_OPT_RECONNECT option:

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

Auto-reconnect was enabled by default until MySQL 5.0.3, and disabled by default thereafter. The MYSQL_OPT_RECONNECT option is available as of MySQL 5.0.13.

If the connection has gone down, the effect of mysql_ping() depends on the auto-reconnect state. If auto-reconnect is enabled, mysql_ping() performs a reconnect. Otherwise, it returns an error.

Some client programs might provide the capability of controlling automatic reconnection. For example, mysql reconnects by default, but the --skip-reconnect option can be used to suppress this behavior.

If an automatic reconnection does occur (for example, as a result of calling mysql_ping()), there is no explicit indication of it. To check for reconnection, call mysql_thread_id() to get the original connection identifier before calling mysql_ping(), then call mysql_thread_id() again to see whether the identifier changed.

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 on the server side and your application will not be notified.

The connection-related state is affected as follows:

If the connection drops, it is possible that the session associated with the connection on the server side will still be running if the server has not yet detected that the client is no longer connected. In this case, any locks held by the original connection still belong to that session, so you may want to kill it by calling mysql_kill().