[Building Sakai] mysql redundant statements (SQL_SELECT_LIMIT)
Lance Speelmon
lance at rsmart.com
Fri Apr 20 07:25:55 PDT 2012
Sounds like it could be this [1]:
1342 if (this.hasLimitClause) {
1343 rowLimit = this.maxRows;
1344 } else {
1345 if (this.maxRows <= 0) {
1346 executeSimpleNonQuery(locallyScopedConn,
1347 "SET OPTION SQL_SELECT_LIMIT=DEFAULT");
[1] http://www.docjar.com/html/api/com/mysql/jdbc/PreparedStatement.java.html
Maybe setting maxRows to a sufficiently high number might prevent it?
On Apr 20, 2012, at 5:19 AM, Stephen Marquard wrote:
> 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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