That doesn't indicate an error. You need to provide more details what made you consider things wedged...
Andres
Thank you very much for the reply. We typically see no visible replication delay over 5 minutes ever. Today we saw a delay of over 3 hours, and no obvious increase in workload either on the provider or the subscriber. I also did not see the LSN advancing whatsoever in terms of applying changes.
I first checked for long-running transactions on the master but there was nothing too unusual except an ANALYZE which I promptly killed, but with no improvement to the situation.
I found the messages above using strace after canceling the subscription and finding that the process was taking extremely long to cancel. There are 2.1 million files in pg_replslot which I don't think is normal? Any ideas as to where I should be looking or what could cause this?