[Deploying Sakai] mysql redundant statements (SQL_SELECT_LIMIT)
Stephen Marquard
stephen.marquard at uct.ac.za
Fri Apr 20 05:19:47 PDT 2012
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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