[flukus]

So this won't help when you have something like a deleted flag and need to join on data that could be in either partition?

[mioelnir]

Yes and no. It won't help in the sense that the query planner can not identify the affected partitions. But it can help if the database supports parallel index scans, since instead of one big index, it has to scan n smaller indexes which can be done concurrently.