On Sun, May 27, 2018 at 5:10 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Instrumenting the test case suggests that getQuadrant pretty much always
> returns 1, resulting in a worst-case unbalanced SPGiST tree. I think this
> is related to the fact that the test case inserts the values in increasing
> order, so that new values are always greater than existing values in the
> index.
I suspected the same. It reminded me of the weird behavior that the
Postgres qsort() sometimes exhibits.
> SPGiST is unable to rebalance its tree on the fly, so it's pretty
> well screwed in this situation. It does finish eventually, but in about
> 50x longer than GiST. I imagine the index's query performance would be
> equally awful.
Can you think of some way of side-stepping the issue? It's unfortunate
that SP-GiST is potentially so sensitive to input order.
--
Peter Geoghegan
