This is based on Jeff's most excellent work to identify why
non-recursive listing under postgreskv was phenomenally slow. It turns
out PostgreSQL's query planner was actually using two sequential scans
of the pathdata table to do its job. It's unclear for how long that has
been happening, but obviously it won't scale any further.
The main change is propagating bucket association with pathnames through
the CTE so that the query planner lets itself use the pathdata index on
(bucket, fullpath) for the skipping-forward part.
Jeff also had some changes to the range ends to keep NULL from being
used- I believe with the intent of making sure the query planner was
able to use the pathdata index. My tests on postgres 9.6 and 11
indicate that those changes don't make any appreciable difference in
performance or query plan, so I'm going to leave them off for now to
avoid a careful audit of the semantic differences.
There is a test included here, which only serves to check that the new
version of the function is indeed active. To actually ensure that no
sequential scans are being used in the query plan anymore, our tests
would need to be run against a test db with lots of data already loaded
in it, and that isn't feasible for now.
Change-Id: Iffe9a1f411c54a2f742a4abb8f2df0c64fd662cb
d5963d81d0