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5.5.3 Error Log Components

This section describes the characteristics of individual error log components. For general information about configuring error logging, see Section 5.4.2, “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 named in the log_error_services system variable value.

  • 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.

The server executes filters and sinks in the log_error_services value in the order they are named. The rightmost component should therefore be a sink. If the rightmost component is a filter, any changes it has on events have no effect on output.

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 to load and unload the component with the INSTALL COMPONENT and UNINSTALL COMPONENT statements.

  • 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.

Error Log Filter 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

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

The log_filter_dragnet Component

Error Log Sink 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 fault of the log_error system variable, determined as described in Section, “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 with INSTALL COMPONENT before use.

  • Multiple uses permitted: No.

  • Output destination: Writes to the default error log destination.

The log_sink_json Component
  • Purpose: Implements JSON-format error logging. See Section, “Error Logging in JSON Format”.

  • URN: file://component_log_sink_json

  • Multiple uses permitted: Yes.

  • Output destination: The JSON log writer 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 JSON writer 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 JSON writer writes to the console. If log_json_writer is named multiple times in the log_error_services value, they all write to the console, which is likely not useful.

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, “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.

The log_sink_test Component
  • Purpose: Intended for internal use in writing test cases. Not intended for production use.

  • URN: file://component_log_sink_test

  • Multiple uses permitted: Yes.

  • Output destination: Writes to the default error log destination.