WL#10942: Logging services: force-print certain non-error messages to error log
Affects: Server-8.0 — Status: Complete — Priority: Medium
There has been a long-standing issue where messages sent through error logging had two particles, a severity and a textual message, and items were filtered on severity (e.g. using --log-error-verbosity). In other words, the severity when chosen at the time of message submission would control both the label ("error", "warning", "note") the message would be printed with AND whether the message would be printed at all (severity vs verbosity). This meant that with a low verbosity ("errors only"), important system messages that were not really errors ("starting", "ready, listening on port ...") had to be tagged as errors to make sure they would be shown, which would lead to some awkward, confusing message of the "error: success" form. Goal of this WL is to introduce a new severity and a label "System" for the system messages and prevent these system messages from discarding using the verbosity filtering.
Func-Req 1 Force-print messages must be written to the error log as [System] instead of [Error], [Warning], [Note] In the "classic" MySQL error log, we have been using labels of "Note", "Warning", and "ERROR". This will remain the case for all events except those listed; events that are "force-printed" will have their labels as "System". Func-Req 2 It should not be possible for the user or DBA to influence [System] and [Error] messages. I.e. they will be printed regardless of verbosity and cannot be suppressed. (Some can indirectly be influenced by SQL mode). Log messages with [Error] label are printed regardless of verbosity and cannot be suppressed now. Even log messages with [System] label will be printed regardless of verbosity and not allowed to suppress. Func-Req 3 [System] messages will be mapped to Linux Syslog and Windows Event log as we do for [Note] messages today. While using system facilities such as Linux SysLog, Windows EventLog and etc, we are limited by the supported severities. Hence the [System] label is mapped to the Note label in linux Syslog and Windows event log. Syslog: * https://en.wikipedia.org/wiki/Syslog Windows Event Log levels: * https://msdn.microsoft.com/en-us/library/office/ff604025(v=office.14).aspx
INTERFACES I-1 SQL syntax No change. I-2 INSTRUMENTATION No change. I-3 ERROR AND WARNINGS No change (but see I-10) I-4 UPGRADE No change. I-5 COMMERCIAL PLUGINS No change. I-6 REPLICATION Certain messages from the replication subsystem will be force-printed, and therefore will appear with variant labels (cf. I-10) in certain log types. (see below for list of messages) I-7 XPROTOCOL No change. I-8 PROTOCOLS No change. I-9 SECURITY No change. I-10 LOG FILES In log-writers that support custom labels, the labels of force-printed messages may appear with label "System". In the context of this WL, this will specifically be the case for the default log-sink, i.e. the traditional MySQL error log file. I-11 MYSQL CLIENTS No change. I-12 AUTH No change. I-13 GLOBALIZATION No change. I-14 CONFIGURATION No change. I-15 FILE FORMATS No change. I-16 PLUGINS/APIS Log-service API's label_from_prio() now shall leave decisions about using custom label "System" to individual log-sinks. This is a refinement only with respect to the new log-sinks added in version 8. (cf. I-10) I-17 MYSQL ADMIN/UTIL/OTHER PROGRAMS No change. I-18 STORAGE ENGINES No change. I-19 DATATYPES No change. MESSAGES The list of messages under consideration for force-printing at this time: ER_STARTING_AS ER_STARTUP ER_XA_STARTING_RECOVERY ER_XA_RECOVERY_DONE ER_NORMAL_SHUTDOWN ER_SHUTDOWN_COMPLETE ER_RPL_SLAVE_CONNECTED_TO_MASTER_REPLICATION_STARTED ER_RPL_SLAVE_CONNECTED_TO_MASTER_REPLICATION_RESUMED ER_SLAVE_CHANGE_MASTER_TO_EXECUTED ER_GTID_PURGED_WAS_CHANGED ER_GTID_EXECUTED_WAS_CHANGED ER_CHANGED_GTID_MODE ER_RPL_SLAVE_DUMP_THREAD_KILLED_BY_MASTER CONSIDERATIONS I - LABELS: NAMES While we can print whatever labels we please in our textual logs, we are limited to supported severities while using system facilities such as syslog, Windows EventLog, etc. It would therefore serve us well to print the messages in question with a label of "Note" or equivalent (e.g. "Information" in syslog/EventLog), rather than to use custom labels ("System") that will print correctly in some logs, but not in others. II - LABELS: Default log-sink. In the default log-sink, force-printed error messages gets the "System" label. New severity "SYSTEM_LEVEL" is introduced in "enum loglevel" for force-printed (or system) messages. III - CAVEATS This mechanism affects message filtering within the server context ("Verbosity is set to low, and this is a [System], but print it anyway!"), i.e. what gets forwarded to log-writer services. For file-writers, the assumption is usually that if we pass a log-event, at least some of its particles (e.g. the message string) are written to its log. Where we forward to OS subsystems though, the configuration of those subsystems also applies; if we "force-print" a error message, we can make sure it arrives in the syslog log-writer service which will pass it on to the OS' syslog facility. We can not however prevent a syslogging daemon configured to do so from throwing away all [Note]s (or logging them to a different destination than [Error]s are). This is a potentially docs- worthy caveat; it is not however a bug: suppose an environment where [Error]s raise an alarm in monitoring -- while "started and listening on port X" may be important, "print always" information, it's not worth waking the admin over. :) INTERFACE The old behaviour of the severity and the label being directly related is retained as a default, as suggested by the principle of the least surprise, by minimum invasive change, and by minimum typing required by other engineers. :)
- New severity (or error level) "SYSTEM_LEVEL" is added to the enum loglevel. - Severity of "SYSTEM_LEVEL" is higher than the "ERROR_LEVEL". - Use "SYSTEM_LEVEL" for the list of calls given in the WL ticket. - sinks can use the value returned by label_from_prio() ("System", "Error", "Warning", "Note") directly. - Sinks(e.g. Linux SysLog and Windows event log) which does not support custom labels "SYSTEM_LEVEL" is mapped to the "INFORMATION_LEVEL". - Behavior with respect to --log-error-verbosity remains the same. Error logs with severity greater than WARNING are always printed.
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