> The SQL spec does not say anything on this respect (that I can find).
> It only talks of "FOR UPDATE" and "FOR READ ONLY". However, because the
> FK code uses SPI to do the locking, we definitely have to expose the
> funcionality through SQL. So I think we need a new clause, which I
> propose to be "FOR SHARE".
MySQL uses LOCK IN SHARE MODE:
http://dev.mysql.com/doc/mysql/en/InnoDB_locking_reads.html