Re: Hash Indexes

On Fri, Sep 30, 2016 at 7:47 AM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> My only firm position is that it wouldn't be very hard to investigate
> hash-over-btree to Andres' satisfaction, say, so, why not? I'm
> surprised that this has caused consternation -- ISTM that Andres'
> suggestion is *perfectly* reasonable. It doesn't appear to be an
> objection to anything in particular.

I would just be very disappointed if, after the amount of work that
Amit and others have put into this project, the code gets rejected
because somebody thinks a different project would have been more worth
doing. As Tom said upthread: $$But to kick the hash AM as such to the
curb is to say
"sorry, there will never be O(1) index lookups in Postgres".$$ I
think that's correct and a sufficiently-good reason to pursue this
work, regardless of the merits (or lack of merits) of hash-over-btree.
The fact that we have hash indexes already and cannot remove them
because too much other code depends on hash opclasses is also, in my
opinion, a sufficiently good reason to pursue improving them. I don't
think the project needs the additional justification of outperforming
a hash-over-btree in order to exist, even if such a comparison could
be done fairly, which I suspect is harder than you're crediting.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company