… often confusing and result in “what does that mean?” questions: Handler_read_rnd Handler_read_rnd_next As I understand it, there is some historical context… was called the handler API, which is why the variables begin with Handler_. Handler_read_rnd counts the number of times the handler::rnd_pos() method is…

… affected (0.00 sec) mysql> show status like ‘Handler_read_rnd_next’ ; +———————–+——-+ | Variable_name | Value | +———————–+——-+ | Handler_read_rnd_next | 0 | +———————–+——-+ 1 row in set (0.00…> show status like ‘Handler_read_rnd_next’ ; +———————–+——-+ | Variable_name | Value | +———————–+——-+ | Handler_read_rnd_next | 4 | +———————–+——-+ 1 row in set (0.00 sec) Handler_read_rnd_next was not incremented…

… call to handler::extra_opt() with HA_EXTRA_CACHE enables the record cache, otherwise known as read buffer, and controlled by read_buffer… SELECT. Scanning the copy the second time does not increment Handler_read_rnd_next. However, scanning the original mysql.user does. So it… mystery that I do not understand, though, is how incrementing Handler_read_rnd_next is avoided on a MyISAM table without the query…

… user FROM user ORDER BY RAND() shows the following: | Handler_read_rnd | 5000 | | Handler_read_rnd_next | 10002 | | Handler_write | 5014 | So, essentially “scan 5000 rows, insert 5000 rows into temp table, sort them with a scan, read…