Comment by cess11

The 5k batching is done when inserting the jobs into the database. It's not like they exert some special control over the performance of the database engine, and this isn't what they're trying to measure in the article.

They spend some time explaining how to tune the job runners to double the 17k jobs/s. The article is kind of old, Elixir 1.14 was a while ago, and it is basically a write-up on how they managed a bit of performance increase by using new features of this language version.