Hi
MONyog’s counter Percentage of full table scans in the Index Usage monitor returns the percentage of the rows accessed via full table scan, the formula for which is as follows:
(Handler_read_rnd_next + Handler_read_rnd) / (Handler_read_rnd_next + Handler_read_rnd + Handler_read_first + Handler_read_next + Handler_read_key + Handler_read_prev)
These values can be obtained from the MySQL server using a simple SHOW GLOBAL STATUS LIKE “%handler%” query. MONyog only reflects the information retrieved from the handler status variables. If you are using MySQL version 5.6.14 or greater then you can enable Custom SQL Object(CSO) in MONyog which will query the performance_schema database to monitor the full table scan. For more details on this please visit: http://www.markleith.co.uk/2012/07/04/mysql-performance-schema-statement-digests/.
The Monitors that you see in MONyog cannot give you such information. They give the values from Status Variables that do not fetch such information. For a full table scan and the relevant query details you can view the Query Analyser. The queries that may cause a problem or may trigger an alert situation would be slow queries, and that can be seen in the query analyser.
Same goes for the details of the table_cache. It is what the status variable opened_tables fetch. There is no option in MySQL to provide you the details of the opened tables. It also depends on the number of max_connections at a time.
Regards
Kartik
