Mysql status variables caveats

While setting up Zenoss and reading Mysql documentation about status variables I learned:

  • All select_* variables ("Select statistics" graph in Zenoss) are actually about joins, not (all) selects. This also explains why there is no clear relation to com_select (which shows the amount of selects). ("Command statistics:selects" graph in Zenoss)
  • Com_select does not denote all incoming select commands. If you have a hit on your query cache, com_select is not incremented. So I thought we were doing less qps while in fact we were just getting more cache hits. Qcache_hits gets incremented on cache hits (but is not monitored by Zenoss)