Vacuum improvement

Hi all,

I'm thinking that there is an improvement to vacuum which could be made
for 7.4. VACUUM FULLing large, heavily updated tables is a pain. There's
very little an application can do to minimise dead-tuples, particularly if
the table is randomly updated. Wouldn't it be beneficial if VACUUM could
have a parameter which specified how much of the table is vacuumed. That
is, you could specify:

VACUUM FULL test 20 precent;

Yes, terrible syntax but regardless: this would mean that we could
spread the vacuum out and not, possibly, be backing up queues. ANALYZE
could be modified, if necessary.

Thoughts?

Gavin