[atombender]

This is a while back, and we've since re-engineered it a bit, but we had database shards processing 400-500 rows/sec, maybe more. Vacuum was not able to keep up even with more aggressive autovacuum settings. (To be fair, the write activity wasn't only to the queue table.)

We were able to show that the dead tuples caused Postgres to use the wrong query plan because it misjudged the amount of real rows. We reported this problem on the Postgres mailing list, and it seemed like this was a known problem and that there was interest in making the planner more dead-tuple-aware.