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.
Beginning with MySQL 8.0.34/8.1.0, the automatic reconnection
feature is deprecated. The related
MYSQL_OPT_RECONNECT option is still
available and functional in MySQL 5.7 but will return a
deprecation warning as of MySQL 8.0.34/8.1.0 to the standard
error output if your application calls the
mysql_options() function with
the option, even when setting it to false.
Expect automatic reconnection functionality to be removed in a future version of MySQL.
Auto-reconnect is disabled by default.
Some client programs might provide the capability of controlling
automatic reconnection. For example, mysql
reconnects by default, but the
option can be used to suppress this behavior.
If an automatic reconnection does occur (for example, as a
result of calling
there is no explicit indication of it. To check for
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.
Reconnection affects the connection-related state as follows:
Rolls back any active transactions and resets autocommit mode.
Releases all table locks.
Closes (and drops) all
Reinitializes session system variables to the values of the corresponding global system variables, including system variables that are set implicitly by statements such as
Loses user-defined variable settings.
Releases prepared statements.
Resets the value of
Releases locks acquired with
Loses the association of the client with the Performance Schema
threadstable row that determines connection thread instrumentation. If the client reconnects after a disconnect, the session is associated with a new row in the
threadstable and the thread monitoring state may be different. See The threads Table.
If reconnection occurs, any SQL statement specified by calling
mysql_options() with the
MYSQL_INIT_COMMAND option is re-executed.
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