Re: BUG #14932: SELECT DISTINCT val FROM table gets stuck in an infinite loop

On 29 January 2018 at 19:11, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> One other point here is that it's not really clear to me what a randomly
> varying IV is supposed to accomplish.  Surely we're not intending that
> it prevents somebody from crafting a data set that causes bad hash
> performance.

I actually think that is a real live issue that we will be forced to
deal with one day. And I think that day is coming soon.

It's not hard to imagine a user of a web site intentionally naming
their objects such that they all hash to the same value. Probably most
systems the worst case is a query that takes a few seconds or even
tens of seconds but if you get lucky you could run a server out of
memory.

I'm actually thinking we should replace all the hashes with
https://en.wikipedia.org/wiki/SipHash with a randomly generated key.

-- 
greg