[Deploying Sakai] mysql redundant statements (SQL_SELECT_LIMIT)

[Stephen Marquard]

Hi all,

I wonder if anyone has come across unusual behaviour with mysql and
this statement:

SET OPTION SQL_SELECT_LIMIT=DEFAULT

If we enable query logging on a test server, there are thousands of
these, mostly redundant in about a 10:1 ratio to real queries. For
example this will get issued over and over again for one connection
(e.g. 1675 below):

                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1678 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1677 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT
                 1675 Query     SET OPTION SQL_SELECT_LIMIT=DEFAULT

The source of this is the mysql connector-j and I've seen the same
behaviour on the latest version (5.1.19) and an older version (5.0.8) so
it doesn't seem to be a recent change. It could be a consequence of some
other change in Sakai or Hibernate though.

We think this is a contributing factor to some performance issues, so
are keen to resolve it.

Regards
Stephen


Stephen Marquard, Acting Director 
Centre for Educational Technology, University of Cape Town
http://www.cet.uct.ac.za
Email/IM/XMPP: stephen.marquard at uct.ac.za 
Phone: +27-21-650-5037 Cell: +27-83-500-5290 
 





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