The Ultimate Guide to High Availability with MariaDB

Query Response Time Plugin

The query_response_time plugin creates the QUERY_RESPONSE_TIME table in the INFORMATION_SCHEMA database. The plugin also adds the SHOW QUERY_RESPONSE_TIME and FLUSH QUERY_RESPONSE_TIME* statements.

The slow query log provides exact information about queries that take a long time to execute. However, sometimes there are a large number of queries that each take a very short amount of time to execute. This feature provides a tool for analyzing that information by counting and displaying the number of queries according to the the length of time they took to execute.

This feature is based on Percona's Response Time Distribution.

Contents

  1. Installing the Plugin
  2. Uninstalling the Plugin
  3. Response Time Distribution
  4. Using the Plugin
    1. Using the Information Schema Table
    2. Using the SHOW Statement
    3. Flushing Plugin Data
  5. Versions
  6. System Variables
    1. query_response_time_flush
    2. query_response_time_range_base
    3. query_response_time_exec_time_debug
    4. query_response_time_session_stats
    5. query_response_time_stats
  7. Options
    1. query_response_time
    2. query_response_time_audit

Installing the Plugin

This shared library actually consists of a number of different plugins. Prior to MariaDB 11.5:

  • QUERY_RESPONSE_TIME - An INFORMATION_SCHEMA plugin that exposes statistics.
  • QUERY_RESPONSE_TIME_AUDIT - audit plugin, collects statistics.

Both plugins need to be installed to get meaningful statistics.

From MariaDB 11.5, there are the following additional plugins:

  • QUERY_RESPONSE_TIME_READ
  • QUERY_RESPONSE_TIME_READ_WRITE
  • QUERY_RESPONSE_TIME_WRITE

Although the plugin's shared library is distributed with MariaDB by default, the plugins are not actually installed by MariaDB by default. There are two methods that can be used to install the plugins with MariaDB.

The first method can be used to install the plugin library without restarting the server. You can install the plugins dynamically by executing INSTALL SONAME or INSTALL PLUGIN. For example:

INSTALL SONAME 'query_response_time';

The second method can be used to tell the server to load the plugin library when it starts up. The plugins can be installed this way by providing the --plugin-load or the --plugin-load-add options. This can be specified as a command-line argument to mysqld or it can be specified in a relevant server option group in an option file. For example:

[mariadb]
...
plugin_load_add = query_response_time

Note that in both cases you have to activate data collection by changing the query_response_time_stats setting to ON, it is OFF by default even when the plugin library is loaded.

You can change the setting at runtime with

SET GLOBAL query_response_time_stats=ON;

or in the options file after the plugin has been loaded:

[mariadb]
...
plugin_load_add = query_response_time
query_response_time_stats=ON;

Uninstalling the Plugin

You can uninstall the plugin dynamically by executing UNINSTALL SONAME or UNINSTALL PLUGIN. For example:

UNINSTALL SONAME 'query_response_time';

If you installed the plugin by providing the --plugin-load or the --plugin-load-add options in a relevant server option group in an option file, then those options should be removed to prevent the plugin from being loaded the next time the server is restarted.

Response Time Distribution

The user can define time intervals that divide the range 0 to positive infinity into smaller intervals and then collect the number of commands whose execution times fall into each of those intervals.

Each interval is described as:

(range_base ^ n; range_base ^ (n+1)]

The range_base is some positive number (see Limitations). The interval is defined as the difference between two nearby powers of the range base.

For example, if the range base=10, we have the following intervals:

(0; 10 ^ -6], (10 ^ -6; 10 ^ -5], (10 ^ -5; 10 ^ -4], ..., 
  (10 ^ -1; 10 ^1], (10^1; 10^2]...(10^7; positive infinity]

or

(0; 0.000001], (0.000001; 0.000010], (0.000010; 0.000100], ..., 
  (0.100000; 1.0]; (1.0; 10.0]...(1000000; positive infinity]

For each interval, a count is made of the queries with execution times that fell into that interval.

You can select the range of the intervals by changing the range base. For example, for base range=2 we have the following intervals:

(0; 2 ^ -19], (2 ^ -19; 2 ^ -18], (2 ^ -18; 2 ^ -17], ..., 
  (2 ^ -1; 2 ^1], (2 ^ 1; 2 ^ 2]...(2 ^ 25; positive infinity]

or

(0; 0.000001], (0.000001, 0.000003], ..., 
  (0.25; 0.5], (0.5; 2], (2; 4]...(8388608; positive infinity]

Small numbers look strange (i.e., don’t look like powers of 2), because we lose precision on division when the ranges are calculated at runtime. In the resulting table, you look at the high boundary of the range.

For example, you may see:

SELECT * FROM INFORMATION_SCHEMA.QUERY_RESPONSE_TIME;
+----------------+-------+----------------+
| TIME           | COUNT | TOTAL          |
+----------------+-------+----------------+
|       0.000001 |     0 |       0.000000 |
|       0.000010 |    17 |       0.000094 |
|       0.000100 |  4301         0.236555 |
|       0.001000 |  1499 |       0.824450 |
|       0.010000 | 14851 |      81.680502 |
|       0.100000 |  8066 |     443.635693 |
|       1.000000 |     0 |       0.000000 |
|      10.000000 |     0 |       0.000000 |
|     100.000000 |     1 |      55.937094 |
|    1000.000000 |     0 |       0.000000 |
|   10000.000000 |     0 |       0.000000 |
|  100000.000000 |     0 |       0.000000 |
| 1000000.000000 |     0 |       0.000000 |
| TOO LONG       |     0 | TOO LONG       |
+----------------+-------+----------------+

This means there were:

* 17 queries with 0.000001 < query execution time < = 0.000010 seconds; total execution time of the 17 queries = 0.000094 seconds

* 4301 queries with 0.000010 < query execution time < = 0.000100 seconds; total execution time of the 4301 queries = 0.236555 seconds

* 1499 queries with 0.000100 < query execution time < = 0.001000 seconds; total execution time of the 1499 queries = 0.824450 seconds

* 14851 queries with 0.001000 < query execution time < = 0.010000 seconds; total execution time of the 14851 queries = 81.680502 seconds

* 8066 queries with 0.010000 < query execution time < = 0.100000 seconds; total execution time of the 8066 queries = 443.635693 seconds

* 1 query with 10.000000 < query execution time < = 100.0000 seconds; total execution time of the 1 query = 55.937094 seconds

Using the Plugin

Using the Information Schema Table

You can get the distribution by querying the the QUERY_RESPONSE_TIME table in the INFORMATION_SCHEMA database. For example:

SELECT * FROM INFORMATION_SCHEMA.QUERY_RESPONSE_TIME;

You can also write more complex queries. For example:

SELECT c.count, c.time,
(SELECT SUM(a.count) FROM INFORMATION_SCHEMA.QUERY_RESPONSE_TIME as a 
   WHERE a.count != 0) as query_count,
(SELECT COUNT(*)     FROM INFORMATION_SCHEMA.QUERY_RESPONSE_TIME as b 
  WHERE b.count != 0) as not_zero_region_count,
(SELECT COUNT(*)     FROM INFORMATION_SCHEMA.QUERY_RESPONSE_TIME) as region_count
FROM INFORMATION_SCHEMA.QUERY_RESPONSE_TIME as c 
  WHERE c.count > 0;

Note: If query_response_time_stats is set to ON, then the execution times for these two SELECT queries will also be collected.

Using the SHOW Statement

As an alternative to the QUERY_RESPONSE_TIME table in the INFORMATION_SCHEMA database, you can also use the SHOW QUERY_RESPONSE_TIME statement. For example:

SHOW QUERY_RESPONSE_TIME;

Flushing Plugin Data

Flushing the plugin data does two things:

Plugin data can be flushed with the FLUSH QUERY_RESPONSE_TIME statement. For example:

FLUSH QUERY_RESPONSE_TIME;

Setting the query_response_time_flush system variable has the same effect. For example:

SET GLOBAL query_response_time_flush=1;

From MariaDB 11.5, it is possible to specify flushing read and/or write statements with the FLUSH QUERY_RESPONSE_TIME_READ, FLUSH QUERY_RESPONSE_TIME_WRITE and FLUSH QUERY_RESPONSE_TIME_READ_WRITE statements.

Versions

VersionStatusIntroduced
1.0StableMariaDB 10.1.13
1.0GammaMariaDB 10.0.10
1.0AlphaMariaDB 10.0.4

System Variables

query_response_time_flush

  • Description: Updating this variable flushes the statistics and re-reads query_response_time_range_base.
  • Commandline: None
  • Scope: Global
  • Dynamic: Yes
  • Data Type: boolean
  • Default Value: OFF

query_response_time_range_base

  • Description: Select base of log for QUERY_RESPONSE_TIME ranges. WARNING: variable change takes affect only after flush.
  • Commandline: --query-response-time-range-base=#
  • Scope: Global
  • Dynamic: Yes
  • Data Type: numeric
  • Default Value: 10
  • Range: 2 to 1000

query_response_time_exec_time_debug

  • Description: Pretend queries take this many microseconds. When 0 (the default) use the actual execution time.
    • This system variable is only available when the plugin is a debug build.
  • Scope: Global
  • Dynamic: Yes
  • Data Type: numeric
  • Default Value: 0
  • Range: 0 to 31536000

query_response_time_session_stats

  • Description: Controls query response time statistics collection for the current session: ON - enable, OFF - disable, GLOBAL (default) - use query_response_time_stats value.
  • Commandline: query-response-time-session-stats=val]
  • Scope: Global, Session
  • Dynamic: Yes
  • Data Type: enum
  • Default Value: GLOBAL
  • Valid Values: GLOBAL, ON, OFF
  • Introduced: MariaDB 11.5

query_response_time_stats

  • Description: Enable or disable query response time statistics collecting.
  • Commandline: query-response-time-stats[={0|1}]
  • Scope: Global
  • Dynamic: Yes
  • Data Type: boolean
  • Default Value: OFF

Options

query_response_time

  • Description: Controls how the server should treat the plugin when the server starts up.
    • Valid values are:
      • OFF - Disables the plugin without removing it from the mysql.plugins table.
      • ON - Enables the plugin. If the plugin cannot be initialized, then the server will still continue starting up, but the plugin will be disabled.
      • FORCE - Enables the plugin. If the plugin cannot be initialized, then the server will fail to start with an error.
      • FORCE_PLUS_PERMANENT - Enables the plugin. If the plugin cannot be initialized, then the server will fail to start with an error. In addition, the plugin cannot be uninstalled with UNINSTALL SONAME or UNINSTALL PLUGIN while the server is running.
    • See Plugin Overview: Configuring Plugin Activation at Server Startup for more information.
  • Commandline: --query-response-time=value
  • Data Type: enumerated
  • Default Value: ON
  • Valid Values: OFF, ON, FORCE, FORCE_PLUS_PERMANENT

query_response_time_audit

  • Description: Controls how the server should treat the plugin when the server starts up.
    • Valid values are:
      • OFF - Disables the plugin without removing it from the mysql.plugins table.
      • ON - Enables the plugin. If the plugin cannot be initialized, then the server will still continue starting up, but the plugin will be disabled.
      • FORCE - Enables the plugin. If the plugin cannot be initialized, then the server will fail to start with an error.
      • FORCE_PLUS_PERMANENT - Enables the plugin. If the plugin cannot be initialized, then the server will fail to start with an error. In addition, the plugin cannot be uninstalled with UNINSTALL SONAME or UNINSTALL PLUGIN while the server is running.
    • See Plugin Overview: Configuring Plugin Activation at Server Startup for more information.
  • Commandline: --query-response-time-audit=value
  • Data Type: enumerated
  • Default Value: ON
  • Valid Values: OFF, ON, FORCE, FORCE_PLUS_PERMANENT

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