Memoization

Memoization is a way to make code run faster by saving
previously computed results. Instead of needing to recompute the value of an
expression, a memoized computation first looks for the value in a cache of pre-
computed values. (caching)

Mathematics for Computer Science

I recommend free online reference:
Mathematics for Computer Science

Bandwith Meter

Here is link for CNET bandwith meter Bandwidth Meter Online Speed Test

restart Drush cron

DELETE FROM variable WHERE name="cron_semaphore";
DELETE FROM variable WHERE name = "cron_last"
drush cc all