How do I… Stress test MySQL with mysqlslap?
One of the interesting new tools in MySQL 5.1.4 is mysqlslap, a load emulator that lets you see how well a particular query set or table engine performs under high-load conditions.
A query that consumes too many database resources may be the result of designing tables incorrectly, choosing the wrong table type, or creating an inefficient query. When a query eats up a lot of database resources, it can negatively affect other application components. By using mysqlslap to stress test a server in a non-public environment, you will discover these errors sooner, allowing you to you avoid a database meltdown once your application goes live.
This tutorial shows how you can use mysqlslap to run stress tests involving multiple clients, custom queries, different table engines, and much more.Basic usage
This simple (and unrealistic) example uses mysqlslap to test server performance assuming only one client connection:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql Benchmark Average number of seconds to run all queries: 0.006 seconds Minimum number of seconds to run all queries: 0.006 seconds Maximum number of seconds to run all queries: 0.006 seconds Number of clients running queries: 1 Average number of queries per client: 0
The —auto-generate-sql switch tells mysqlslap to automatically generate and execute SQL statements, monitor how fast MySQL performs this task, and display the result. The results indicate that MySQL took 0.006 seconds to execute the SQL statements.
The —auto-generate-sql switch creates a table, executes an INSERT query and saves dummy data to it, executes a SELECT query to retrieve the dummy data, and then drops the table. You can see behind-the-scenes action by adding the -v switch to the mysqlslap command line (adding extra ‘v’s increases the verbosity level):
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql -vv DROP SCHEMA IF EXISTS `mysqlslap`; CREATE SCHEMA `mysqlslap`; CREATE SCHEMA `mysqlslap`; CREATE TABLE `t1` (intcol1 INT(32),charcol1 VARCHAR(128)); INSERT INTO t1 VALUES (1804289383,'mxvtvmC9127qJNm06sGB8R92q2j7vTiiITRDGXM9ZLzkdekbWtmXKwZ2qG1llkRw5m9DHOFilEREk3q7oce8O3BEJC0woJsm6uzFAEynLH2xCsw1KQ1lT4zg9rdxBL'); SELECT intcol1,charcol1 FROM t1; Benchmark Average number of seconds to run all queries: 0.007 seconds Minimum number of seconds to run all queries: 0.007 seconds Maximum number of seconds to run all queries: 0.007 seconds Number of clients running queries: 1 Average number of queries per client: 0 DROP SCHEMA IF EXISTS `mysqlslap`;
It’s unlikely that you’ll have only a single client connecting to the MySQL server at any given time, so you’ll typically also need the —concurrency switch, which lets you simulate multiple simultaneous client connections, like this:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 Benchmark Average number of seconds to run all queries: 0.698 seconds Minimum number of seconds to run all queries: 0.698 seconds Maximum number of seconds to run all queries: 0.698 seconds Number of clients running queries: 100 Average number of queries per client: 0
MySQL performance drops pretty significantly (from 0.007 seconds to 0.698 seconds) when it has to deal with 100 clients instead of just one.
See what happens if you increase the number of concurrent connections even more:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=300 Benchmark Average number of seconds to run all queries: 47.515 seconds Minimum number of seconds to run all queries: 47.515 seconds Maximum number of seconds to run all queries: 47.515 seconds Number of clients running queries: 300 Average number of queries per client: 0
Note: As you increase the number of concurrent connections, you might encounter a « Too many connections » error. You need to adjust MySQL’s ‘max_connections’ variable, which controls the maximum number of concurrent connections allowed by the server.
Running tests more than once
You can force mysqlslap to run a particular test more than once by adding the —iterations switch to the command line. This example runs the same test five times and prints a composite result:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —iterations=5 Benchmark Average number of seconds to run all queries: 0.714 seconds Minimum number of seconds to run all queries: 0.682 seconds Maximum number of seconds to run all queries: 0.753 seconds Number of clients running queries: 100 Average number of queries per client: 0
Specifying the total number of queries
It’s possible to force each « client » to run a specific number of queries by adding the —number-of-queries switch to the mysqlslap command line. When mysqlslap encounters this switch, it divides the corresponding value by the number of concurrent connections and uses the result to decide how many queries each client should run.
For example, with settings of 500 total queries and five concurrent clients, mysqlslap will run 500/5 = 100 queries per client. Take a look at an example:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-of-queries=10000 Benchmark Average number of seconds to run all queries: 0.694 seconds Minimum number of seconds to run all queries: 0.694 seconds Maximum number of seconds to run all queries: 0.694 seconds Number of clients running queries: 100 Average number of queries per client: 100
Using larger tables
The default behavior of mysqlslap when using the —auto-generate-sql switch is to create a two-column table with one integer column and one character column. If this isn’t representative of the kind of tables you typically use, you can adjust these settings to include more integer and/or character columns, with the —number-char-cols and —number-int-cols switches. Here are examples:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-of-queries=1000 —number-char-cols=4 —number-int-cols=7 Benchmark Average number of seconds to run all queries: 1.290 seconds Minimum number of seconds to run all queries: 1.290 seconds Maximum number of seconds to run all queries: 1.290 seconds Number of clients running queries: 100 Average number of queries per client: 100 shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-char-cols=4 Benchmark Average number of seconds to run all queries: 0.968 seconds Minimum number of seconds to run all queries: 0.968 seconds Maximum number of seconds to run all queries: 0.968 seconds Number of clients running queries: 100 Average number of queries per client: 0 shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-int-cols=5 Benchmark Average number of seconds to run all queries: 1.076 seconds Minimum number of seconds to run all queries: 1.076 seconds Maximum number of seconds to run all queries: 1.076 seconds Number of clients running queries: 100 Average number of queries per client: 0
Using custom queries
While the —auto-generate-sql option is fine for general load testing, you may want to test the performance of a specific query on a database that already exists. In these situations, you can bypass the —auto-generate-sql switch and instead tell mysqlslap to use your own custom query with the —query switch. Here’s the next example:
shell> /usr/local/mysql/bin/mysqlslap —user=john —create-schema=world —query="SELECT City.Name, City.District FROM City, Country WHERE City.CountryCode = Country.Code AND Country.Code = 'IND';" —concurrency=100 —iterations=5 Benchmark Average number of seconds to run all queries: 2.886 seconds Minimum number of seconds to run all queries: 2.137 seconds Maximum number of seconds to run all queries: 4.125 seconds Number of clients running queries: 100 Average number of queries per client: 1
It’s helpful to use mysqlslap in this manner when you need to analyze the effect of a change in your database structure or indexing because it allows you to immediately grasp the impact of, say, an additional index on overall performance. To illustrate, look what happens to the time needed to run the previous query when an index is added to the City table:
mysql> CREATE INDEX idx_ccode ON City(CountryCode); Query OK, 4079 rows affected (1.06 sec) Records: 4079 Duplicates: 0 Warnings: 0 mysql> exit Bye shell> /usr/local/mysql/bin/mysqlslap —user=john —create-schema=world —query="SELECT City.Name, City.District FROM City, Country WHERE City.CountryCode = Country.Code AND Country.Code = 'IND';" —concurrency=100 —iterations=5 Benchmark Average number of seconds to run all queries: 1.682 seconds Minimum number of seconds to run all queries: 1.396 seconds Maximum number of seconds to run all queries: 2.109 seconds Number of clients running queries: 100 Average number of queries per client: 1
You can tell mysqlslap to create a custom table for your load testing by using the —create command-line switch with a CREATE TABLE command.
Comparing table engines
A cool feature of mysqlslap is the ability to specify the table engine used in the test. This provides database designers with an easy way to compare the performance of different table types under different load conditions. The —engine switch accepts any of MySQL’s supported table types and creates test tables using the corresponding storage engine. Here’s an example of how it could be used:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-of-queries=700 —engine=innodb Benchmark Running for engine innodb Average number of seconds to run all queries: 1.240 seconds Minimum number of seconds to run all queries: 1.240 seconds Maximum number of seconds to run all queries: 1.240 seconds Number of clients running queries: 100 Average number of queries per client: 7 shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-of-queries=700 —engine=myisam Benchmark Running for engine myisam Average number of seconds to run all queries: 0.676 seconds Minimum number of seconds to run all queries: 0.676 seconds Maximum number of seconds to run all queries: 0.676 seconds Number of clients running queries: 100 Average number of queries per client: 7 shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-of-queries=700 —engine=memory Benchmark Running for engine memory Average number of seconds to run all queries: 0.602 seconds Minimum number of seconds to run all queries: 0.602 seconds Maximum number of seconds to run all queries: 0.602 seconds Number of clients running queries: 100 Average number of queries per client: 7
Saving reports
You might wish to save a mysqlslap report so you can compare it to a previous or future test run; you may also want to use the report as a reference when you’re configuring new systems.
The easiest way to save a mysqlslap report is to pipe the output of a mysqlslap run to a file, as below:
shell> /usr/local/mysql/bin/mysqlslap —user=john —auto-generate-sql —concurrency=100 —number-of-queries=1000 —number-char-cols=4 —number-int-cols=7 >> /tmp/output.log
You can force mysqlslap to generate reports in CSV format; this is often useful if you need to import the data into a spreadsheet or database to build graphical reports from it. To do this, add the —csv switch to your mysqlslap command line and specify the output filename as an argument to this switch. Here’s an example:
shell> /usr/local/mysql/bin/mysqlslap —csv=/tmp/output.csv —user=john —auto-generate-sql —concurrency=100 —number-of-queries=1000 —number-char-cols=4 —number-int-cols=7
Here’s what the CSV file would contain if you peeked inside it:
shell> cat /tmp/output.csv,query,1.070,1.070,1.070,100,10
Trying mysqlslap
The mysqlslap utility makes it possible to benchmark and compare MySQL performance on different hardware, as well as accurately quantify the effect of a change in database design. Try mysqlslap out for yourself and see how well your database server behaves under pressure from thousands of client connections.