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Finding random subsets

Suppose you have a large set of records and you need to process them in random batches over longer period of time. By "random batches" I mean subsets, containing random elements from the full set. The solution we've found working good for us is based on the following steps:
  1. Load unprocessed record ids into memory;
  2. Periodically extract a random batch of ids;
  3. Process extracted records and persist them as processed.
The tricky part of the process is step 2). How do you efficiently find random subset of a big set? It turns out there is a ready-made algorithm for this - https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle. Following is the JavaScript implementation, which proved to be useful in the context of the aforementioned task:

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