Is MySQL X faster than MySQL Y? – Ask queryprofiler

When trying out new software there are many other questions you may ask and one of those is going to be the one above. The answer requires you to have built your software to capture and record low level database metrics and often the focus of application developers is slightly different: they focus on how fast the application runs, but do not pay direct attention to the speed of each MySQL query they generate, at least under normal circumstances. So often they are not necessarily able to answer the question.

I have been evaluating MySQL 5.7 for some time, but only since its change to GA status has the focus has switched to check for any remaining issues and also to determine if in the systems I use performance is better or worse than MySQL 5.6.  The answers here are very application and load specific and I wanted a tool to help me answer that question more easily.

Since MySQL 5.6, the performance_schema database has had a table performance_schema.events_statements_summary_by_digest which shows collected metrics on normalised versions of queries. This allows you to see which queries are busiest and gives you some metrics on those queries such as minimum, maximum and average query times.

I used this information and built queryprofiler to allow me to collect these metrics in parallel from one or more servers and thus allow me to compare the behaviour of these servers against each other. This allows me to answer the question that had been nagging me for some time in a completely generic way.  It should also work on MariaDB 10.0 and later though I have not had time to try that out yet.

queryprofiler works slightly differently to just querying P_S once. It takes several collections of the data, computes deltas between each collection thus allowing you to know things like the number of queries per second which events_statements_summary_by_digest does not tell you. (There is no information in performance_schema telling you when the collections start. That is something I miss and would like to see fixed in MySQL 5.8 if possible.)

The other difference of course is that P_S gives you information on one server. If you collect the information at the same time from more than one server with a similar load then the numbers you get out should be very similar and that is what queryprofiler does.

How do you use queryprofiler?  Provide it with one or more Go-style MySQL DSNs to connect to the servers and optionally tell it how many times to collect data from the servers (default: 10) and at what interval (default: every second) and it will run and give you the results, telling you the top queries seen (by elapsed time of the query) and the metrics for each server (queries per second, average query latency and how much these values vary).

A couple of examples of the output can be found here:

Hopefully you will find this tool useful.  Feedback and patches to improve it are most welcome.

Published by

Simon J Mudd

Born in England, I now live in Spain, but spent a few years living in the Netherlands. I previously worked in banking (financial markets) both in IT and as a broker, but IT has always had a stronger influence. Now working at as a Senior Database Administrator. Other interests include photography, and travel. Simon is married, with two children and lives in Madrid.

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