It appears to be an intentional change, made in scope of MDEV-4981. Assigning to sanja to double-check that it was really thought through, and if so, get the documentation be updated accordingly.
Would love to get this double-checked as well, a lot of tools to measure query stats depend heavily on the Com_select and Qcache_hits values, this also means people using tools such as Munin, or Graphite will need to make very MariaDB specific code, since else you'll get graphs like this:
It would be nice if we can use most MySQL plugins for monitoring, since MariaDB is advertised as "An enhanced, drop-in replacement for MySQL". Then we should also be able to measure data/statistics the same way, but with additional features. I believe you can achieve the same data you want in MDEV-4981 by combining some numbers from the Com_* and Qcache_* variables.
Oleksandr Byelkin will you look into this?
Of course I will (when come its time)
The case is looks simple, but there is non-simple question why it was changed which needs time to figure out.
Any news about this?
OK, it is bug in the documentation. the work was done according to https://mariadb.atlassian.net/browse/MDEV-4981.
Docs will be fixed soon.
@sanja / Oleksandr - so there won't be done anything regarding this issue? It still doesn't count correctly.
A Com_select should never get incremented if you also have a Qcache_hit
Thank you a lot! I've fixed the documentation.
It's not documentation, but it actually counts wrong in the internals. Try launch mytop, or mysqltuner, or anything that calculates your query hit ratio, you'll never get above 50% because MariaDB increments Com_select on a query cache hit.
Looking at MySQL it doesn't do this, which makes completely sense, it breaks every graph made for MySQL (and MariaDB since it's a drop-in replacement).
Oleksandr,
https://screenshots.lucasrolff.com/2016_02_07_k4k0gl3pojf0h70.png
As you can see - according to the graph I'm doing 994.67 queries per second - what I actually do on the server is 557 queries per second.
Here's a screenshot from when we switched to MariaDB - our queries didn't increase, but since MariaDB increments Com_select when it shouldn't it results in graphs that are wrong:
https://screenshots.lucasrolff.com/2016_02_07_2vxrdrebh9zi198.png
Please reopen this.
Just to make it clear. in 5.5 behaviour changed and you should not add QC hits. And we are really sorry for the mess in the documentation but we have just fixed it.
So if you upgraded to 5.5 and up you should calculate statistics in other way.
We use munin official mysql plugins - these calculate correctly in MySQL (both version 5.1, 5.5, 5.6) but in MariaDB counts incorrectly.
MySQL 5.5+ does not increase Com_select when Qcache_hits gets incremented.
You probably have to complain to the plugin producer.
Sorry, but mariadb has different set of statistics in general and in this particular place also.