Hiya,
I've been having trouble running vacuumdb -a and pg_dumpall
concurrently because they run through the databases in a different
order (so dumpall was getting stuck behind vacuum's lock, and my
firewall was rather unhelpfully closing the idle connection). I can't
see a good reason for them to
Um, whaddya mean "dumpall was getting stuck behind vacuum's lock"?
A plain vacuum doesn't take any locks that would block pg_dump.
Dammit, just looked and the setup I originally encountered the problem
on and tracked it down to the vacuum process, and it is indeed set up
to perform a full vacuum