从性能上说，不会有任何影响。
http://dev.mysql.com/doc/refman/5.6/en/innodb-consistent-read.html

Consistent read is the default mode in which InnoDB processes SELECT statements in READ COMMITTED and REPEATABLE READ isolation levels. A consistent read does not set any locks on the tables it accesses, and therefore other sessions are free to modify those tables at the same time a consistent read is being performed on the table.

InnoDB的缺省隔离级别是REPEATABLE READ，Consistent non-blocking read是缺省模式。也就是说select不会被update block住。这被称为mvcc。