I was looking into a MySQL performance issue with one of my teammates when I ran into this odd little quirk.
Older versions of MySQL come with a set of sample configuration files (
my-huge.cnf) suitable for systems with varying resources and workloads.
my-huge.cnf files set a value for the
thread_concurrency variable and suggest, “Try number of CPU’s*2 for thread_concurrency.” Since we were working on a 4-core system, setting a value of 8 seemed like a good idea.
Except, as it turns out, it’s basically worthless.
thread_concurrency only works on old versions of Solaris and does nothing at all on other OSes. Which makes one wonder why it’s included in the sample configuration files…