Space-wise, it's cheaper to create a new table and select data into it, rather than using the built-in cluster function in postgres.

While cluster would perform exactly the operation we want, it's massively costly.

And while pg_repack can do on-line clustering, it requires a unique constraint on the table, which is something you usually don't have for measurements. ( Putting one across all fields could work, but that'd just cause a pita)