Greg Stark <gsstark(at)mit(dot)edu> writes:
> You say it's "*very* busy" is it possible there are hundreds or thousands of
> tuples in there that are uncommitted or committed after this query starts?
More specifically, I bet there's a huge number of completely empty
pages, which would be read by a seqscan but not an indexscan. VACUUM
FULL should fix it nicely, but it's odd that autovacuum isn't keeping
a lid on the file size. Maybe with so few live rows, it's confused into
thinking it doesn't need to vacuum the table often?
regards, tom lane