This function is useful in replication for controlling primary/replica synchronization. It blocks until the replica has read and applied all updates up to the specified position (
log_name,log_pos) in the primary log. The return value is the number of log events the replica had to wait for to advance to the specified position. The function returns NULL if
the replica SQL thread is not started, the replica's primary information is not
initialized, the arguments are incorrect, or an error occurs. It returns -1 if
the timeout has been exceeded. If the replica SQL thread stops while
MASTER_POS_WAIT() is waiting, the function returns NULL. If
the replica 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.