We are lately experiencing very strange locks on PostgreSQL 11.7 when we process ETL tasks using our programs in Go 1.13.8 using standard libraries sql and pq.
ETL task has to rename tables but PostgreSQL shows that this simple operation waits for Lock on relation and select from PG wiki (https://wiki.postgresql.org/wiki/Lock_Monitoring) which should show blocking process shows that command "alter table .... rename to ...." is blocked by process "COPY .... to stdout" but from completely different table.
And from time to time even selects from some tables seem to by blocked by copy commands running on other tables. This is shown by the same select from PG wiki for blocking queries.
All this stuff runs from golang programs. So maybe problem is not on PostgreSQL but in golang libraries?