LG-8060 | Fetch from Redis in batches

[n1zyy]

changelog: Internal, Attempts API, Fetch from Redis in batches

🎫 Ticket

LG-8060

🛠 Summary of changes

This story was initially for a series of changes to the background job. Ultimately, none gave a performance improvement, except that reading in batches could be slightly faster, depending on batch size.

But, @zachmargolis pointed out that, because Redis is single-threaded, it's much kinder to Redis to read in batches rather than one gigantic hgetall. That's the big win; the performance improvement is very marginal.

I initially coded this to call hscan inside a loop, introduced a lulzy infinite loop where we ran until counter == 0 when counter was actually returned as a string, and then realized while looking at the source that hscan_each already did what I wanted. I have progressively whittled this down to just a few lines.

Note that this will fetch from Redis in batches, but it still builds everything up in one big array before returning it. We may some day want to accept a block to allow us to operate on batches. Today is not that day, though -- the existing EnvelopeEncryptor code expects that we have the whole payload in memory.

[n1zyy]

This is never passed in, but I'm leaving it to allow tinkering in rails c, unless rubocop yells.

[Rwolfe-Nava]

Looks good to me! Excited for this change!