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Re: MySqlPlugin
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Re: MySqlPlugin

  • Subject: Re: MySqlPlugin
  • From: Mark Gowdy <email@hidden>
  • Date: Fri, 07 Mar 2014 18:29:47 +0000
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@hidden> 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@hidden> 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

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Robin Smith
Engineering Team Leader  BEng (Hons) MBCS

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References: 
 >MySqlPlugin (From: Robin Smith <email@hidden>)
 >Re: MySqlPlugin (From: Jesse Tayler <email@hidden>)
 >Re: MySqlPlugin (From: Robin Smith <email@hidden>)

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