This function is useful in replication for controlling master/slave synchronization. It blocks until the slave has read and applied all updates up to the specified position (
log_name,log_pos) in the master log. The return value is the number of log events the slave had to wait for to advance to the specified position. The function returns NULL if
the slave SQL thread is not started, the slave's master information is not
initialized, the arguments are incorrect, or an error occurs. It returns -1 if
the timeout has been exceeded. If the slave SQL thread stops while
MASTER_POS_WAIT() is waiting, the function returns NULL. If
the slave is past the specified position, the function returns immediately.
timeout value is specified,
timeout seconds have elapsed.
timeout must be greater than 0; a
zero or negative
timeout means no
Statements using the MASTER_POS_WAIT() function are not safe for replication.