Database Server Logs¶
Galera Cluster provides the same database server logging features available to MySQL, MariaDB and Percona XtraDB, depending on which you use. By default, it writes errors to a <hostname>.err file in the data directory. You can change this in the my.cnf configuration file using the log_error option, or by using the --log-error parameter.
Log Parameters
Galera Cluster provides parameters and wsrep options that allow you to enable error logging on events that are specific to the replication process. If you have a script monitoring the logs, these entires can give you information on conflicts occurring in the replication process.
wsrep_log_conflicts: This parameter enables conflict logging for error logs. An example would be when two nodes attempt to write to the same row of the same table at the same time.
cert.log_conflicts: This wsrep Provider option enables logging of information on certification failures during replication.
wsrep_debug: This parameter enables debugging information for the database server logs.
Warning
In addition to useful debugging information, this parameter also causes the database server to print authentication information, (i.e., passwords) to the error logs. Don’t enable it in production environments as it’s a security vulnerability.
You can enable these through the my.cnf configuration file. The excerpt below is an example of these options and how they are enabled:
# wsrep Log Options
wsrep_log_conflicts=ON
wsrep_provider_options="cert.log_conflicts=ON"
wsrep_debug=ON
Additional Log Files
Whenever a node fails to apply an event on a slave node, the database server creates a special binary log file of the event in the data directory. The naming convention the node uses for the filename is GRA_*.log.
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