Re: Question about RUM-index

On Wed, Jun 15, 2016 at 3:56 AM, Andreas Joseph Krogh <andreas(at)visena(dot)com>
wrote:

> Hi.
>
> First; Is this the correct forum to ask questions about the Postgres Pro's
> new RUM-index?
>
> If not, please point me to the right forum.
>

I think that https://github.com/postgrespro/rum/issues might be the best
forum.

>
> Note that GIN does almost what I want, except use the index when sorting
> by "sent"-timestamp.
>
> So I wonder if RUM can do any better?
> What I don't understand is how to have "folder_id" as part of the
> RUM-index so that I can search in *an array* of folders using the index,
> *AND* have the whole result sorted by "sent"-timestamp also using the
> RUM-index.
>

I think you would have to implement an operator for integers for RUM much
like btree_gin does for GIN. Sorry don't know how to do that, except to
say look in the RUM code to see how it does it for time-stamps.

>
> In the (limited) documentation sorting using timestamp is done like this:
>
> ORDER BY sent <-> '2000-01-01'::TIMESTAMP
>
> which I don't understand; Why must one specify a value here, and how does
> that value affect the result?
>

This is essentially identical to ORDER BY ABS(sent -
'2000-01-01'::TIMESTAMP); except it can use the index.

So maybe pick a constant outside the range of possible values, and use that
as one argument to <->.

Cheers,

Jeff