7.5.3 Error Log Components

This section describes the characteristics of individual error log components. For general information about configuring error logging, see Section 7.4.2, “The Error Log”.

A log component can be a filter or a sink:

A filter processes log events, to add, remove, or modify event fields, or to delete events entirely. The resulting events pass to the next log component in the list of enabled components.
A sink is a destination (writer) 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. A sink may also write to the Performance Schema error_log table; see Section 29.12.22.2, “The error_log Table”. Events pass unmodified to the next log component in the list of enabled components (that is, although a sink formats events to produce output messages, it does not modify events as they pass internally to the next component).

The log_error_services system variable lists the enabled log components. Components not named in the list are disabled. log_error_services also implicitly loads error log components if they are not already loaded. For more information, see Section 7.4.2.1, “Error Log Configuration”.

The following sections describe individual log components, grouped by component type:

Component descriptions include these types of information:

The component name and intended purpose.
Whether the component is built in or must be loaded. For a loadable component, the description specifies the URN to use if explicitly loading or unloading the component with the INSTALL COMPONENT and UNINSTALL COMPONENT statements. Implicitly loading error log components requires only the component name. For more information, see Section 7.4.2.1, “Error Log Configuration”.
Whether the component can be listed multiple times in the log_error_services value.
For a sink component, the destination to which the component writes output.
For a sink component, whether it supports an interface to the Performance Schema error_log table.

Filter Error Log Components

Error log filter components implement filtering of error log events. If no filter component is enabled, no filtering occurs.

Any enabled filter component affects log events only for components listed later in the log_error_services value. In particular, for any log sink component listed in log_error_services earlier than any filter component, no log event filtering occurs.

The log_filter_internal Component

Purpose: Implements filtering based on log event priority and error code, in combination with the log_error_verbosity and log_error_suppression_list system variables. See Section 7.4.2.5, “Priority-Based Error Log Filtering (log_filter_internal)”.
URN: This component is built in and need not be loaded.
Multiple uses permitted: No.

If log_filter_internal is disabled, log_error_verbosity and log_error_suppression_list have no effect.

The log_filter_dragnet Component

Purpose: Implements filtering based on the rules defined by the dragnet.log_error_filter_rules system variable setting. See Section 7.4.2.6, “Rule-Based Error Log Filtering (log_filter_dragnet)”.
URN: file://component_log_filter_dragnet
Multiple uses permitted: No.

Sink Error Log Components

Error log sink components are writers that implement error log output. If no sink component is enabled, no log output occurs.

Some sink component descriptions refer to the default error log destination. This is the console or a file and is indicated by the value of the log_error system variable, determined as described in Section 7.4.2.2, “Default Error Log Destination Configuration”.

The log_sink_internal Component

Purpose: Implements traditional error log message output format.
URN: This component is built in and need not be loaded.
Multiple uses permitted: No.
Output destination: Writes to the default error log destination.
Performance Schema support: Writes to the error_log table. Provides a parser for reading error log files created by previous server instances.

The log_sink_json Component

Purpose: Implements JSON-format error logging. See Section 7.4.2.7, “Error Logging in JSON Format”.
URN: file://component_log_sink_json
Multiple uses permitted: Yes.
Output destination: This sink determines its output destination based on the default error log destination, which is given by the log_error system variable:
- If log_error names a file, the sink bases output file naming on that file name, plus a numbered .NN.json suffix, with NN starting at 00. For example, if log_error is file_name, successive instances of log_sink_json named in the log_error_services value write to file_name.00.json, file_name.01.json, and so forth.
- If log_error is stderr, the sink writes to the console. If log_sink_json is named multiple times in the log_error_services value, they all write to the console, which is likely not useful.
Performance Schema support: Writes to the error_log table. Provides a parser for reading error log files created by previous server instances.

The log_sink_syseventlog Component

Purpose: Implements error logging to the system log. This is the Event Log on Windows, and syslog on Unix and Unix-like systems. See Section 7.4.2.8, “Error Logging to the System Log”.
URN: file://component_log_sink_syseventlog
Multiple uses permitted: No.
Output destination: Writes to the system log. Does not use the default error log destination.
Performance Schema support: Does not write to the error_log table. Does not provide a parser for reading error log files created by previous server instances.

The log_sink_test Component

Purpose: Intended for internal use in writing test cases, not for production use.
URN: file://component_log_sink_test

Sink properties such as whether multiple uses are permitted and the output destination are not specified for log_sink_test because, as mentioned, it is for internal use. As such, its behavior is subject to change at any time.