Yann Michel <yann-postgresql(at)spline(dot)de> writes:
> Well, now that I'm thinking about, what you've written I think this is
> exactly the point. I think, that there is a VACUUM waiting for the dump
> to finish whereas the INSERTS are waiting for the VACUUM to finish.
Only if it's a VACUUM FULL ... plain VACUUM neither blocks INSERT nor is
blocked by pg_dump.
The short answer may be "don't use VACUUM FULL" (at least not for
routine automatic vacuums).
regards, tom lane