Webinar replay: MySQL Query Tuning Trilogy: Query tuning process and tools

Copyright 2016 Severalnines AB

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Your host & some logistics

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About Severalnines and ClusterControl


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What we do

Manage Scale

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Customers


MySQL Query Tuning - Process & Tools

August 30, 2016

Krzysztof Książek

Severalnines

[email protected]

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mailto:[email protected]


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Agenda

! Query tuning process

! Build

! Collect

! Analyze

! Tune

! Test

! Tools

! tcpdump

! pt-query-digest


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The process


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The process! A short guide to query performance review:

! Build test environment

! Collect your data

! Process your data

! Analyze your data

! Tune SQL and schemas

! Test changes

! Apply changes on production systems


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The process - build test environment

! You need a deterministic, test environment to make sure you can measure the impact of the changes

! Environment should mirror production as close as possible, to make it more relevant

! Hardware makes a difference, especially I/O - you’ll see different performance if your I/O subsystem is slow

! Dataset makes even more significant difference - you should test your new queries against production dataset

! If you need to obfuscate your data, your results may be different than on production systems


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The process - build test environment

! The best way to build a test system is to grab a backup of your production systems

! Restore it on a host which matches hardware configuration of the production

! You are all set

! Ideally, you have such QA/staging/dev environment up and running all the time and use it to test your new code and SQL

! If not, build it at least couple times per year to run such a review

! If you are using ClusterControl and Galera Cluster, take advantage of the cloning feature


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The process - collect your data

! Native method - slow query log

! Collects the most important data about the query:


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! It can collect even more data on Percona Server and MariaDB:

! Even more data with log_slow_verbosity='full,profiling_use_getrusage,profiling'


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The process - collect your data! Another method - tcpdump

! Capture TCP traffic containing MySQL queries

! Gives limited information about the query:

! Query execution time

! Query size

! Main advantage - not necessary to execute it on the MySQL host - this reduces the impact

! Proxy

! Application host


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The process - analyze your data

! Thousands of lines in the log - can’t parse it manually

! You can build your own tool to aggregate data from slow query log

! Or you can use industry standard - pt-query-digest:

! wget http://percona.com/get/pt-query-digest && chmod u+x ./pt-query-digest

! Run pt-query-digest against slow query log or tcpdump

! But not on the database host - it can be CPU and memory intensive

! It’ll provide you with a summary of the traffic along with detailed information about each and every query

http://percona.com/get/pt-query-digest


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The process - tune SQL and schemas

! Use EXPLAIN to check the query execution plan

! Rewrite queries to your liking

! Test new indexes, remove obsolete ones

! Make sure the new query execution plan works better

! Leverage Performance Schema for deep dive into where query execution time goes


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The process - apply changes on production systems

! Make sure you know what impact your changes will have

! If you run detailed tests in the test environment, you should be good

! Execute your changes

! Directly

! Using pt-online-schema-change

! Make sure you monitor the system after the change

! Have a rollback plan

! A list of ALTERs which will revert your changes can be really handy when things go awry

! Make sure you monitor how things unravel for at least couple of days - some processes may be executed on a weekly basis (or even less often)


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The tools


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The tools - tcpdump

! Collects a snapshot of the TCP traffic

! When you capture MySQL traffic, it contains enough data to calculate:

! Query execution time

! Query size

! Not much of details but enough to pinpoint slow queries

! You can always check details later, via EXPLAIN

! tcpdump -s 65535 -x -nn -q -tttt -i any port 3306 > mysql.tcp.txt

! Run it on the MySQL host

! Run it on the application server

! Run it on the proxy node

! Great flexibility - you can easily avoid most of the overhead caused by the tool


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The tools - pt-query-digest

! Amazing tool which is designed to aggregate data located in slow query log

! It can work with (among others) slow log and tcpdump output

! Presents the data in a very nice way

! Summary of all of the queries

! Each query presented in a detailed way (if there’s enough data for it, that is)

! EXPLAIN ready for copy&paste

! Report can be modified to user’s liking

! Sort queries by numerous attributes

! Aggregate queries differently

! Ability to store data in the database helps to build a solid review process

! You can also compare old query performance data with current one - to confirm performance has not changed


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! pt-query-digest --limit=100% /var/lib/mysql/slow.log > ptqd1.out

! Report starts with a summary:

! How many queries?

! How many distinct queries?


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! Large amount of summarized data

! Helps to understand query patterns

! Helps to understandhow workload has changed


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! Queries in the report are sorted - by default, by total query execution time.

! Each query has a Query ID assigned - a hash of the query digest


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! Extensive information about every query. Extra data for Percona Server and MariaDB.


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! Detailed InnoDB stats:

! All the data: I/O operations, lock waits, pages accessed


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! Query histogram

! EXPLAIN

! SHOW commands


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! Data from tcpdump can’t be as detailed as from slow log

! It still can be used to generate important statistics

! You can always analyze such querymanually later


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The tools - ClusterControl Query Monitor

! ClusterControl provides a continuous view into query performance

! Query Monitor presents query performance data based on Performance Schema (preferred) or slow query log (if Performance Schema is not available)

! May not be suitable for a “grand” review, but will help significantly on a day-to-day basis

! Query Histogram section lists queries with variable execution time - something definitely worth looking into


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Thank You!! Blog posts covering query tuning process:

! http://severalnines.com/blog/become-mysql-dba-blog-series-query-tuning-process

! http://severalnines.com/blog/become-mysql-dba-blog-series-analyzing-your-sql-workload-using-pt-query-digest

! http://severalnines.com/blog/become-mysql-dba-blog-series-deep-dive-sql-workload-analysis-using-pt-query-digest

! Register for the next part of our trilogy:

! http://severalnines.com/upcoming-webinars

! Install ClusterControl:

! http://severalnines.com/getting-started

! Contact: [email protected]

http://severalnines.com/blog/become-mysql-dba-blog-series-query-tuning-process

http://severalnines.com/blog/become-mysql-dba-blog-series-analyzing-your-sql-workload-using-pt-query-digest

http://severalnines.com/blog/become-mysql-dba-blog-series-deep-dive-sql-workload-analysis-using-pt-query-digest

http://severalnines.com/upcoming-webinars

http://severalnines.com/getting-started

mailto:[email protected]

Webinar replay: MySQL Query Tuning Trilogy: Query tuning process and tools

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