In MySQL 8.0, error logging uses the MySQL component architecture described at Section 5.5, “MySQL Components”. The error log subsystem consists of components that perform log event filtering and writing, as well as a system variable that configures which components to enable to achieve the desired logging result.
This section discusses how to select components for error logging. For instructions specific to log filters, see Section 18.104.22.168, “Types of Error Log Filtering”. For instructions specific to the JSON and system log sinks, see Section 22.214.171.124, “Error Logging in JSON Format”, and Section 126.96.36.199, “Error Logging to the System Log”. For additional details about all available log components, see Section 5.5.3, “Error Log Components”.
Component-based error logging offers these features:
Log events can be filtered by filter components to affect the information available for writing.
Log events are output by sink (writer) components. Multiple sink components can be enabled, to write error log output to multiple destinations.
Built-in filter and sink components combine to implement the default error log format.
A loadable sink enables logging in JSON format.
A loadable sink enables logging to the system log.
System variables control which log components to enable and how each component operates.
variable controls which log components to enable for error
logging. The variable may contain a list with 0, 1, or many
elements. In the latter case, elements may be delimited by
semicolon or (as of MySQL 8.0.12) comma, optionally followed by
space. A given setting cannot use both semicolon and comma
separators. Component order is significant because the server
executes components in the order listed.
has this value:
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
log_sink_internal sink component,
both of which are built in. 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 final component in the
cannot be a filter. This is an error because any changes it
has on events would have no effect on output:
mysql> SET GLOBAL log_error_services = 'log_filter_internal'; ERROR 1231 (42000): Variable 'log_error_services' can't be set to the value of 'log_filter_internal'
To correct the problem, include a sink at the end of the value:
mysql> SET GLOBAL log_error_services = 'log_filter_internal; log_sink_internal'; Query OK, 0 rows affected (0.00 sec)
The combination of
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
The output destination is determined by the
--log-erroroption (and, on Windows,
--console). These determine whether to write error messages to the console or a file and, if to a file, the error log file name. See Section 188.8.131.52, “Default Error Log Destination Configuration”.
log_error_suppression_listsystem variables affect which types of log events
log_filter_internalpermits or suppresses. See Section 184.108.40.206, “Priority-Based Error Log Filtering (log_filter_internal)”.
To change the set of log components used for error logging, load
components as necessary, perform any component-specific
configuration, and modify the
Adding or removing log components is subject to these
To add a log component to the list of enabled components:
Load the component using
INSTALL COMPONENT(unless it is built in or already loaded).
If the component exposes any system variables that must be set for component initialization to succeed, assign those variables appropriate values.
Enable the component by listing it in the
For a component to be permitted in the
log_error_servicesvalue, it must be known. A component is known if it is built in, or if it is loadable and has been loaded using
INSTALL COMPONENT. Attempts to name an unknown component at server startup cause
log_error_servicesto be set to its default value. Attempts to name an unknown component at runtime produce an error and the
log_error_servicesvalue remains unchanged.
For example, to use the system log sink
log_sink_syseventlog) instead of the default
log_sink_internal), first load the sink
component, then modify the
INSTALL COMPONENT 'file://component_log_sink_syseventlog'; SET GLOBAL log_error_services = 'log_filter_internal; log_sink_syseventlog';
The URN to use for loading a log component with
INSTALL COMPONENT is the
component name prefixed with
file://component_. For example, for the
log_sink_syseventlog component, the
corresponding URN is
It is possible to configure multiple log sinks, which enables
sending output to multiple destinations. To enable the system
log sink in addition to (rather than instead of) the default
sink, set the
log_error_services value like
SET GLOBAL log_error_services = 'log_filter_internal; log_sink_internal; log_sink_syseventlog';
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_syseventlog';
To configure a log component to be enabled at each server startup, use this procedure:
If the component is loadable, load it at runtime using
INSTALL COMPONENT. Loading the component registers it in the
mysql.componentsystem table so that the server loads it automatically for subsequent startups.
log_error_servicesvalue at startup to include the component name. Set the value either in the server
my.cnffile, or use
SET PERSIST, which sets the value for the running MySQL instance and also saves the value to be used for subsequent server restarts; see Section 220.127.116.11, “SET Syntax for Variable Assignment”. A value set in
my.cnftakes effect at the next restart. A value set using
SET PERSISTtakes effect immediately, and for subsequent restarts.
Suppose that you want to configure, for every server startup,
use of the JSON log sink (
addition to the built-in log filter and sink
log_sink_internal). First load the JSON sink
if it is not loaded:
INSTALL COMPONENT 'file://component_log_sink_json';
take effect at server startup. You can set it in
[mysqld] log_error_services='log_filter_internal; log_sink_internal; log_sink_json'
Or you can set it using
SET PERSIST log_error_services = 'log_filter_internal; log_sink_internal; log_sink_json';
log_filter_internal; log_sink_1; log_sink_2
In this case, log events pass to the built-in filter, then to the first sink, then to the second sink. Both sinks receive the filtered log events.
Compare that to this
log_sink_1; log_filter_internal; log_sink_2
In this case, log events pass to the first sink, then to the built-in filter, then to the second sink. The first sink receives unfiltered events. The second sink receives filtered events. You might configure error logging this way if you want one log that contains messages for all log events, and another log that contains messages only for a subset of log events.
If the 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
log_sink_json sinks support
this capability. See
Section 18.104.22.168, “The error_log Table”.