Re: Deprecating Hash Indexes

On 15 October 2012 18:07, Robert Haas <robertmhaas@gmail.com> wrote:
> On Mon, Oct 15, 2012 at 12:59 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>>> I don't think I'd go so far as to say that we should
>>> imply that they'll be removed in a future release.  Given how deeply
>>> intertwined they are with the planner, I doubt that that will happen;
>>> and I think there is enough interest in the technology that it's
>>> likely to eventually be fixed.
>>
>> Hash indexes aren't used in the planner. Hash joins use completely
>> separate code.
>
> It's not really completely separate, because to do a hash join we have
> to find a hash function for the relevant data types, and IIUC we do
> that by looking up the default hash opclass for the datatype and
> finding its first support function.  Of course, if we were to remove
> the hash AM, then you couldn't define a hash opclass against it.

Presumably it defaults to hash_any() but I get the picture.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services