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Displaying posts with tag: optimizer_switch (reset)
"I'm Winston Wolf, I solve problems."

My (few) readers are probably somewhat tired of boring topics of metadata locks and gdb breakpoints that I discuss a lot this year, so for this weekend I decided to concentrate on something less technical but still important to me - the way I prefer to follow while providing support for MySQL.

Before I continue, it's time to add the explicit disclaimer: the views on how support engineer should work expressed below are mine alone and not those of my current (or any previous) employer. Specific case I describe may be entirely fictional and has nothing to do with any real life customer. I love thy customers in reality... …

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Back on disk temporary tables

We already blog a lot on temporary tables on disk, how this could be bad for your workload and should be avoid.  Each temporary table will open a file descriptor,  external kernel call and by nature a well know file system slow operation.

We can point this benchmark simulating a working mail server


Monitoring of such queries can be trace via the status of

created_tmp_disk_tables 
Evidence of what is happening watching many Aria or MyISAM tables created on disk :

/usr/sbin/lsof  | grep "mysql" | grep "#"
mysqld     1855     mysql 1658u      REG                8,1       8192    1505932 …

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Showing entries 1 to 2