Analyze MySQL Performance
When asked to analyze the performance of a MySQL or MariaDB server, there are two main tasks
(tuning and slowlog) I like to start with.
The groundwork for them can be done by the customer.
The deliverables:
⚈ Short list of settings (VARIABLES) to change in my.cnf.
⚈ Recommendations for speeding up the 'worst' queries.
⚈ (possibly) Schema or Architectural recommendations.
In doing these tasks, I get a feel for what the system is doing, thereby jumpstarting any further involvement with the customer's site.
The tuning is usually a one-time task, but may be rerun as the
data grows and/or major changes are made to the application.
The Slowlog analysis should be rerun periodically.
Tuning
Please provide
⚈ How much RAM in the server
⚈ SHOW VARIABLES; -- the tunables
⚈ SHOW GLOBAL STATUS; -- various metrics
⚈ (If sys is installed) SELECT * FROM sys.metrics;
Please take GLOBAL STATUS after the server has been running at least 24 hours.
(Otherwise things like 'cold cache' invalidate some of the findings.)
The SHOWs need to be in machine readable format.
Privacy: There is nothing very sensitive in the SHOWs.
However, if you are especially paranoid, you could mask out any ip addresses and host names.
Nothing significant will be lost from the analysis.
With those, I will use an automated script compute about 200 formulas and check for reasonable values.
Usually about 20 are flagged as 'suspect'.
Then I review them the results and clean up things.
The bottom line is a few concrete recommendations for
⚈ Changing a few variables.
⚈ (maybe) Converting away from MyISAM. (I have tips on the task, if you have not yet done such.)
⚈ (maybe) Turn off the Query cache. (Perhaps under 5% of Production systems benefit from the QC.)
⚈ (probably) Turning on and analyzing the slowlog (below).
If you choose to post online, see a free tool such as
⚈ justpaste.it
⚈ pastebin
Slow queries and Slowlog
MySQL and MariaDB optionally create a "slowlog" file or table.
Setup:
⚈ Set long_query_time = 1 -- Preferrable in my.cnf We may change that threshold up or down later, but this is a reasonable start.
⚈ Set up the slowlog to be captured to FILE.
⚈ Turn on (the details of this vary with the Version)
⚈ Wait at least 24 hours.
Writing slow_log to file -- this is preferred, since there are tools for condensing such:
log_output = FILE
slow_query_log = ON
slow_query_log_file = (fullpath to some file)
long_query_time = 1
log_slow_admin_statements = ON
log_queries_not_using_indexes = OFF
Notes:
⚈ log_output can be TABLE to write to mysql.slow_log, or FILE,TABLE to write both
⚈ slow_query_log_file has a default; is not needed for TABLE
⚈ long_query_time is a float, and can be as low as 0, but that gets verbose; default is a 'useless' 10
⚈ log_slow_admin_statements tend to be slow but infrequent
⚈ log_queries_not_using_indexes is mostly clutter; simply worry about those that are slow
⚈ If running on a Replica, consider using log_slow_slave_statements
⚈ Beginning with 8.0.14, also have log_slow_extra = ON
Other options (version dependent; incomplete):
log_slow_rate_limit=100
log_slow_rate_type=query
log_slow_verbosity=full
slow_query_log_always_write_time=1
slow_query_log_use_global_control=all
innodb_monitor_enable=all
userstat=1
Gather results for me (preferrably using FILE):
⚈ Digest the results using either of these:
pt-query-digest
mysqldumpslow -s t
⚈ Grab the first few (perhaps 5) queries. They will be sorted by (frequency * avg-time), which is the most useful.
⚈ Provide SHOW CREATE TABLE -- for each table
⚈ Provide EXPLAIN SELECT ... -- for each query
Analyze Results:
Usually (not always), I can then provide a concrete suggestion on speeding up each query:
⚈ Add a particular index (often 'composite')
⚈ Reformulate the query (a simple case is not hiding an indexed column in a function; more complex involves adding/removing subqueries)
⚈ Recommend schema change
⚈ Possibly even an architectural change (EAV is a common problem)
Where to get pt-query-digest
pt-query-digest
Download the "Percona toolkit".
If you are using a cloud service, you may not be able to get to the slowlog file. See if there is a UI that provides a way to download it. It may also provide a way to set up the slowlog paramterers.
Windows
The Percona toolkit does "not" work on Windows. But it seems that the only limitation with the slowlog is "end-of-line". Change CRLF to LF throughout the slowlog; then pt-query-digest should work.
Some common recommendations:
Many-to-Many mapping schema
Speeding up wp_postmeta
explode-implode problem of JOIN + GROUP BY
Pagination via OFFSET - instead "remember where you left off"
More tips are found in the links below.
Posted June, 2017;
Slowlog: Sep, 2017
Partition Maintenance (DROP+REORG) for time series (includes list of PARTITION uses)
Big DELETEs - how to optimize -- and other chunking advice, plus a use for PARTITIONing
Chunking lengthy DELETE/UPDATE/etc.
Data Warehouse techniques:
Data Warehouse Overview
Summary Tables
High speed ingestion
Bulk Normalization
Schema and code design for large Sensor database
Entity-Attribute-Value (EAV) -- a common, poorly performing, design pattern; plus an alternative
Lat/Lng search to Find the nearest 10 pizza parlors
Lat/Long representation choices
Pagination, not with OFFSET, LIMIT
Techniques on efficiently finding a random row (On beyond ORDER BY RAND())
GUID/UUID Performance (type 1 only)
IP Range Table Performance -- or other disjoint ranges
Alter of a Huge table -- Mostly obviated by 5.6
Efficient List of Latest 10 news articles
Build and execute a Pivot SELECT (showing rows as columns)
(Groupwise Max): Efficiently find largest row(s) for each group
Other Tips, Tuning, Debugging, Optimizations, etc...
Rick's RoTs (Rules of Thumb -- lots of tips)
Datatypes and building a good schema
Memory Allocation (caching, etc)
Character Set and Collation problem solver
Trouble with UTF-8
If you want case folding, but accent sensitivity, please file a request at https://bugs.mysql.com .
Python tips,
PHP tips,
other language tips
utf8 Collations
utf8mb4 Collations on 8.0
Converting from MyISAM to InnoDB -- includes differences between them
Compound INDEXes plus other insights into the mysteries of INDEXing
Cookbook for Creating Indexes
Many-to-many mapping table
Handler counts
wp_postmeta
UNION+OFFSET
MySQL Limits -- built-in hard limits
767-byte INDEX limit
Galera, tips on converting to (Percona XtraDB Cluster, MariaDB 10, or manually installed)
5.7's Query Rewrite -- perhaps 5.7's best perf gain, at least for this forum's users
Analyze MySQL Performance
Analyze VARIABLEs and GLOBAL STATUS
Analyze SlowLog
My slides from conferences
MiniFest 2021 - Rick James & Daniel Black - Answering on Stack Overflow(+comments) - MariaDB Frontlines
Percona Live 4/2017 - Rick's RoTs (Rules of Thumb) - MySQL/MariaDB
Percona Live 4/2017 - Index Cookbook - MySQL/MariaDB
Percona Live 9/2015 - PARTITIONing - MySQL/MariaDB
Contact me via LinkedIn; be sure to include a brief teaser in the Invite request:
