Re: Question about RUM-index

På torsdag 16. juni 2016 kl. 00:50:45, skrev Jeff Janes <jeff(dot)janes(at)gmail(dot)com
<mailto:jeff(dot)janes(at)gmail(dot)com>>:
On Wed, Jun 15, 2016 at 3:56 AM, Andreas Joseph Krogh <andreas(at)visena(dot)com
<mailto: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
<https://github.com/postgrespro/rum/issues> might be the best forum.

 
Oleg and friends; Should we use GitHub-issues as forum (one issue per
question/thread?), pgsql-general or something else?
 
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 <->.

 
This should be unnecessary and hidden from the user. Maybe some "ORDER BY
rum_timestamp(sent)" or something could abstract away stuff to make it much
clearer to the user?

-- Andreas Joseph Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
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