> And I am climbing out of the rabbit hole that is Postgres' CLUSTER keyword :) Really funky, looks like it's a one-time operation that isn't persisted?

Correct. If you're in a situation that needs it, you'll need to run it at some interval. I have it running once a week on one of our databases.

Also, postgres uses this to solve a problem that clustered indexes on other databases don't solve - a clustered index isn't necessarily on an index you care about for querying. It still has to go back to the table data to get fields not in that index, which could have a random-access performance penalty if you're getting a lot of rows. Postgres's CLUSTER changes the order of the table data to match an index, which allows a sequential read on the disk, avoiding that performance penalty.

This is one of the situations where people complain the postgres query planner is doing the wrong thing and they want hints to tell it to use the index, but the query planner is actually protecting them from a huge random-disk-access performance penalty they don't realize they'd hit if they did that. The right thing to do is either use CLUSTER or, if they're on an SSD or the data can all fit in memory, change the random-access-penalty config value so the query planner no longer takes this into account.