OSC_DEBUG_DB_EXPLAIN constant, added in version 2.3, run an
EXPLAIN query for each select query and logs the result to a file called explain_queries.log queries. It should be used only during the development of OSClass, themes or plugins to see the performance of the queries. Remember, if Apache doesn't have write permissions, you may need to create the file first and set the appropriate permissions (i.e. use 666).