15.16.2.1. Starting a Transaction from a start_stmt() Call
The first function call that can start a transaction is the
start_stmt()
function.
The following example shows how a storage engine could
register a transaction:
int my_handler::start_stmt(THD *thd, thr_lock_type lock_type)
{
int error= 0;
my_txn *txn= (my_txn *) thd->ha_data[my_handler_hton.slot];
if (txn == NULL)
{
thd->ha_data[my_handler_hton.slot]= txn= new my_txn;
}
if (txn->stmt == NULL && !(error= txn->tx_begin()))
{
txn->stmt= txn->new_savepoint();
trans_register_ha(thd, FALSE, &my_handler_hton);
}
return error;
}
THD is the current client connection. It
holds state relevant data for the current client, such as
identity, network connection and other per-connection data.
thd->ha_data[my_handler_hton.slot] is a
pointer in thd to the connection-specific
data of this storage engine. In this example we use it to
store the transaction context.
An additional example of implementing
start_stmt() can be found in
ha_innodb.cc.
