Re: No Index-Only Scan on Partial Index

On Tuesday, October 1, 2013, David E. Wheeler <david(at)justatheory(dot)com> wrote:
> On Oct 1, 2013, at 3:56 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>
>> I don't think it has anything to do with the conditional index -- it's
>> the functional based. For some reason postgres always wants to post
>> filter (note the filter step below):
>>
>> postgres=# create index on try(upper_inf(irange));
>> CREATE INDEX
>> Time: 12.001 ms
>> postgres=# explain select * from try where upper_inf(irange);
>> QUERY PLAN
>>
-------------------------------------------------------------------------------
>> Index Scan using try_upper_inf_idx on try (cost=0.00..9.25 rows=33
width=40)
>> Index Cond: (upper_inf(irange) = true)
>> Filter: upper_inf(irange)
>
> Hrm. I get a seq scan for that query:
>
> create index on try(upper_inf(irange));
> explain select * from try where upper_inf(irange);
> QUERY PLAN
> -----------------------------------------------------------
> Seq Scan on try (cost=0.00..1887.00 rows=33333 width=68)
> Filter: upper_inf(irange)
>
> True also if I just select the irange. Is the filter the issue, here?

Turn off seq scan...

merlin