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The error log contains a record of mysqld startup and shutdown times. It also contains diagnostic messages such as errors, warnings, and notes that occur during server startup and shutdown, and while the server is running. For example, if mysqld notices that a table needs to be automatically checked or repaired, it writes a message to the error log. Depending on error log configuration, error messages may also populate the Performance Schema error_log table, to provide an SQL interface to the log and enable its contents to be queried. If the error log grows abnormally or if the administrators notice a sudden/abnormal increase in the count of errors/warnings logged in the error log, the performance of the target database server instance may go in for a toss. To ensure smooth functioning of the database server, administrators need to periodically check for the errors/warnings logged in the error log and initiate pre-emptive measures to fix them. For this purpose, administrators can use the MySQLErrLogTesttest.

This test periodically monitors the error log of the target database server and reports the count of errors and warnings logged in the error log. This test also reports the total file size of the error log and the growth rate of the log file. Use the detailed diagnostics of this test to figure out when exactly were the errors/warnings noticed and what was the cause of such errors/warnings.

Outputs of the test : One set of results for the target database server instance being monitored.

Measurement	Description	Measurement Unit	Interpretation
Error_count	Indicates the number errors logged in the error log.	Number	The detailed diagnosis of this measure lists the Error time, Warning Time and the Message relevant to the error.
Warning_count	Indicates the number of warnings logged in the error log.	Number	The detailed diagnosis of this measure lists the Error time, Warning Time and the Message relevant to the warning.
File_size	Indicates the current size of the error log.	MB
Growth_rate	IndIndicates the rate at which the error log file had grown during the last measurement period.	MB/sec	A high value for this measure or a consistent increase in its value indicates that the error log is rapidly growing and may end up occupying too much space on the disk.