This might be unrelated, but we experience an issue where our apps would periodically freeze. From memory, LIMIT might have been a factor. It was solved by upgrading the mysql-connector-java jar from 3.1.8 to 5.1.16
> By examining the state of the hung instance, we saw that the mysql connector > class ReadAheadInputStream was just sitting with a constant socketRead. > > So, it turned out that it is a problem in the mysql-connector-java-3.1.8.jar > See: > - http://bugs.mysql.com/bug.php?id=9515 > - http://bugs.mysql.com/bug.php?id=31353 > > Those links describe the bug i.e. Hangs in ReadAheadInputStream.fill() > > We upgraded from: > mysql-connector-java-3.1.8.jar > to > mysql-connector-java-5.1.26.jar > > and the problem went away. > > This may also have been the cause of an occasional freezing of our instances > (which was happening infrequently and randomly). We had to force-quit them > to get them going again. Mark On 7 Mar 2014, at 18:20, Robin Smith wrote: > I'm not sure about fetch plans, all i know at the moment is if i remove the > LIMIT query i get millisecond performance on my query but if i include a > LIMIT clause i get a full table scan. > > > On 7 March 2014 17:15, Jesse Tayler <[email protected]> wrote: > did you check to make sure your database is using the index fetch plan you > expect? > > I recall with MySQL sometimes indexes would fail but there would be no > indication until I actually reviewed the fetch internals… > > something chuck would know off the top of his head I’m sure… > > > > > On Mar 7, 2014, at 12:02 PM, Robin Smith <[email protected]> wrote: > >> Hi All >> >> We have been experiencing some performace issues with our DB queries that we >> have narrowed down to the "limitClause" applied to sql queries. It seems >> that out of the box MySQL uses no indexes when supplied with a LIMIT clause. >> >> Taking this into consideration we were wondering if anything like batch >> fetch iterator rely on the limit clause being applied to queries or if we >> could safely remove (or add switch to) this part of _MySqlPlugin. >> >> Thanks >> >> Robin >> >> -- >> Robin Smith >> Engineering Team Leader BEng (Hons) MBCS >> >> http://www.clicktravel.com >> >> Think: Do you really need to print this email? >> _______________________________________________ >> Do not post admin requests to the list. They will be ignored. >> Webobjects-dev mailing list ([email protected]) >> Help/Unsubscribe/Update your Subscription: >> https://lists.apple.com/mailman/options/webobjects-dev/jtayler%40oeinc.com >> >> This email sent to [email protected] > > > > > -- > Robin Smith > Engineering Team Leader BEng (Hons) MBCS > > http://www.clicktravel.com > > Think: Do you really need to print this email? > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Webobjects-dev mailing list ([email protected]) > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/webobjects-dev/gowdy%40mac.com > > This email sent to [email protected]
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