The log_error_services system variable controls which loadable log components to load, and which log components to enable for error logging. By default, log_error_services has the value shown here:

mysql> SELECT @@GLOBAL.log_error_services;
+----------------------------------------+
| @@GLOBAL.log_error_services            |
+----------------------------------------+
| log_filter_internal; log_sink_internal |
+----------------------------------------+

That value indicates that log events first pass through the log_filter_internal filter component, then through the log_sink_internal sink component, both of which are built-in components. A filter modifies log events seen by components named later in the log_error_services value. A sink is a destination for log events. Typically, a sink processes log events into log messages that have a particular format and writes these messages to its associated output, such as a file or the system log.

The combination of log_filter_internal and log_sink_internal implements the default error log filtering and output behavior. The action of these components is affected by other server options and system variables:

When configuring log_error_services, be aware of the following characteristics:

Error log configuration involves loading and enabling error log components as necessary and performing component-specific configuration.

There are two error log configuration methods, implicit and explicit. It is recommended that one configuration method is selected and used exclusively. Using both methods can result in warnings at startup. For more information, see Troubleshooting Configuration Issues.

This procedure describes how to load and enable error logging components implicitly using log_error_services. For a discussion of error log configuration methods, see Error Log Configuration Methods.

To load and enable error logging components implicitly:

To disable a log component, remove it from the log_error_services value. Also remove any associated component variables settings that you have defined.

This procedure describes how to load and enable error logging components explicitly by loading components using INSTALL COMPONENT and then enabling using log_error_services. For a discussion of error log configuration methods, see Error Log Configuration Methods.

To load and enable error logging components explicitly:

To disable a log component, remove it from the log_error_services value. Then, if the component is loadable and you also want to unload it, use UNINSTALL COMPONENT. Also remove any associated component variables settings that you have defined.

Attempts to use UNINSTALL COMPONENT to unload a loadable component that is still named in the log_error_services value produce an error.

If you have previously loaded error log components explicitly using INSTALL COMPONENT and want to switch to an implicit configuration, as described in Implicit Error Log Configuration, the following steps are recommended:

If you need to revert from an implicit configuration to an explicit configuration, perform the following steps:

Log components listed in the log_error_services value at startup are loaded implicitly early in the MySQL Server startup sequence. If the log component was loaded previously using INSTALL COMPONENT, the server attempts to load the component again later in the startup sequence, which produces the warning Cannot load component from specified URN: 'file://component_component_name'.

You can check for this warning in the error log or by querying the Performance Schema error_log table using the following query:

SELECT error_code, data
  FROM performance_schema.error_log
 WHERE data LIKE "%'file://component_%"
   AND error_code="MY-013129" AND data LIKE "%MY-003529%";

To prevent this warning, follow the instructions in Changing the Error Log Configuration Method to adjust your error log configuration. Either an implicit or explicit error log configuration should be used, but not both.

A similar error occurs when attempting to explicitly load a component that was implicitly loaded at startup. For example, if log_error_services lists the JSON log sink component, that component is implicitly loaded at startup. Attempting to explicitly load the same component later returns this error:

mysql> INSTALL COMPONENT 'file://component_log_sink_json';
ERROR 3529 (HY000): Cannot load component from specified URN: 'file://component_log_sink_json'.

It is possible to configure multiple log sinks, which enables sending output to multiple destinations. To enable the JSON log sink in addition to (rather than instead of) the default sink, set the log_error_services value like this:

SET GLOBAL log_error_services = 'log_filter_internal; log_sink_internal; log_sink_json';

To revert to using only the default sink and unload the system log sink, execute these statements:

SET GLOBAL log_error_services = 'log_filter_internal; log_sink_internal;
UNINSTALL COMPONENT 'file://component_log_sink_json';

If enabled log components include a sink that provides Performance Schema support, events written to the error log are also written to the Performance Schema error_log table. This enables examining error log contents using SQL queries. Currently, the traditional-format log_sink_internal and JSON-format log_sink_json sinks support this capability. See Section 29.12.22.2, “The error_log Table”.