5.4.2.8 Error Log Message Format

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Each error log sink (writer) component has a characteristic output format it uses to write messages to its destination, but other factors may influence the content of the messages:

The information available to the log writer. If a log filter component executed prior to execution of the writer component removes a log event attribute, that attribute is not available for writing. For information about log filtering, see Section 5.4.2.3, “Types of Error Log Filtering”.
System variables may affect log writers. See System Variables That Affect Error Log Format.

For all log writers, the ID included in error log messages is that of the thread within mysqld responsible for writing the message. This indicates which part of the server produced the message, and is consistent with general query log and slow query log messages, which include the connection thread ID.

Output Format for log_sink_internal

This log writer produces the traditional error log output. It writes messages using this format:

timestamp thread_id [priority] [err_code] [subsystem] message

The [ and ] square bracket characters are literal characters in the message format. They do not indicate that fields are optional.

The [err_code] and [subsystem] fields were added in MySQL 8.0. They will be missing from logs generated by older servers. Log parsers can treat these fields as parts of the message text that will be present only for logs written by servers recent enough to include them. Parsers must treat the err_code part of [err_code] indicators as a string value.

Examples:

2018-03-22T12:35:47.538083Z 0 [Note] [MY-012487] [InnoDB] InnoDB: DDL log recovery : begin
2018-03-22T12:35:47.550565Z 0 [Warning] [MY-010068] [Server] CA certificate /var/mysql/sslinfo/cacert.pem is self signed.
2018-03-22T12:35:47.669397Z 4 [Note] [MY-010051] [Server] Event Scheduler: scheduler thread started with id 4
2018-03-22T12:35:47.550939Z 0 [Note] [MY-010253] [Server] IPv6 is available.

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Output Format for log_sink_json

The JSON-format log writer produces messages as JSON objects that contain key-value pairs. For example:

{ "prio": 3, "err_code": 10051, "subsystem": "Server",
  "source_file": "event_scheduler.cc", "function": "run",
  "msg": "Event Scheduler: scheduler thread started with id 4",
  "time": "2018-03-22T12:35:47.669397Z", "thread": 4,
  "err_symbol": "ER_SCHEDULER_STARTED", "SQL_state": "HY000",
  "label": "Note" }

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Output Format for log_sink_syseventlog

The system log writer produces output that conforms to the system log format used on the local platform.

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Output Format for Early-Startup Logging

The server generates some error log messages before startup options have been processed, and thus before it knows error log settings such as the log_error_verbosity and log_timestamps values, and which log components are to be used. The server handles error log messages that are generated early in the startup process as follows:

Prior to MySQL 8.0.14, the server generates messages with the default timestamp, format, and verbosity level, and buffers them. After the startup options are processed and the error log configuration is known, the server flushes the buffered messages. Because these early messages use the default log configuration, they may differ from what is specified by the startup options. Also, the early messages are not flushed to log writers other than the default. For example, logging to the JSON writer does not include these early messages because they are not in JSON format.
As of MySQL 8.0.14, the server buffers log events rather than formatted log messages. This enables it to retroactively apply configuration settings to those events after the settings are known, with the result that flushed messages use the configured settings, not the defaults. Also, messages are flushed to all configured writers, not just the default writer.
If a fatal error occurs before log configuration is known and the server must exit, the server so they are not lost. If no fatal error occurs but startup is excessively slow prior to processing startup options, the server periodically formats and flushes buffered messages using the logging defaults so as not to appear unresponsive. Although these behaviors are similar to pre-8.0.14 behavior in that the defaults are used, they are preferable to losing messages when exceptional conditions occur.

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System Variables That Affect Error Log Format

The log_timestamps system variable controls the time zone of timestamps in messages written to the error log (as well as to general query log and slow query log files). Permitted values are UTC (the default) and SYSTEM (local system time zone).

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Document created the 26/06/2006, last modified the 26/10/2018
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References

Manuel MySQL : https://dev.mysql.com/

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