Eternal DataFileRead on partition seeks after upgrade? Or in general..

Hi all.

I have a table that is partitioned by month. It contains rows of plays per
a game, with about 800k rows per game, and maybe about 350 games per month.
Its PK is a game identifier, a play identifier, and the game's date as that
is partition key.

It's a lot of data, I think.

Before upgrading to 13, it used to be a reasonable amount of time to pull
records based on multiple game identifiers (even if it was a few
million rows).

Since upgrading to 13, it seems it is endlessly waiting on DataFileRead to
query this table, and things take hours.

I'm wondering what I can do: is the bottleneck truly the disk I/O (it
wasn't really a disk issue before).

I did run vacuumdb --analyze-only after upgrade, but if doing anything
else: re-indexing the PK, etc, might help these queries seek the proper
partition more quickly (guessing that is what is happening with
the DataFileRead), I'd be eager to learn.

Thank you.

--
Wells Oliver
wells(dot)oliver(at)gmail(dot)com <wellsoliver(at)gmail(dot)com>