https://medium.com/@rajagopals/activerecord-on-mysql-iterating-over-large-tables-with-conditions-453bd8761c8b . In a high volume analytics system, tables with millions of records are quite common and iterating over the full table or a subset of these tables becomes often necessary  — whether it’s to perform computations, run a migration, or create parallelized background jobs on the records. It becomes important to write efficient code for iterations because there is often an order of magnitude difference between a good and not-so-good approac