Jeff Janes <jeff.janes@gmail.com> writes:
> I believe the rationale was so that an autovacuum would still look like it
> was needed, and get fired again the next naptime, so that it could continue
> with the truncation attempts. (Rather than waiting for 20% turnover in the
> table before trying again). I'm not convinced by this argument. If the
> DBA is desperate to get the space back, they can go do vacuum full.
Well, that's why I think the lock abandonment shouldn't apply to manual
plain vacuum. You shouldn't need to do a vacuum full for that; that'd
be a huge increase in the cost, not to mention that it'd transiently
require twice the disk space, hardly a good thing if you're short.
regards, tom lane