[dev] shares performance hit (was Re: disable shares)

[duck]

On Tue, 2008-06-10 at 14:23 +0200, Didi Rieder wrote:
> Well now (2 PM) there are about 1,000 active user sessions, mysql is  
> running with 10-20 threads. mytop shows that almost all the vislible  
> queries shares queries. I the moment when the machine produced the  
> slow queries hundreds of threads were running. I also noticed that I  
> have to increase the max number of allowed open files.

With this amount of data and traffic you should not increase the number
of open files. As this is a symptom of missconfig. First enlarge
the tmp_table_size. Myql server creates internal temporary tables while
processing queries. If an in-memory temporary table exceeds the limit,
MySQL automatically converts it to an on-disk MyISAM table. This must be
avoided as mush as possible. With all your ram this should not be a
problem. By default is 32MB. Bring it up to 200M.Then force mysql to
have more threads by default (let say thread_cache_size = 50). So in
average you always have a thread fee waiting for a new connection. 


Duck