Re: Searching GIN-index (FTS) and sort by timestamp-column

On Sat, Mar 19, 2016 at 5:44 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> On Wed, Mar 16, 2016 at 6:53 AM, Andreas Joseph Krogh <andreas(at)visena(dot)com>
> wrote:
>
>> På onsdag 16. mars 2016 kl. 14:37:27, skrev Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>>
>> Andreas Joseph Krogh <andreas(at)visena(dot)com> writes:
>> > 1. Why isnt' folder_id part of the index-cond?
>>
>> Because a GIN index is useless for sorting.
>>
>> > 2. Is there a way to make it use the (same) index to sort by
>> > received_timestamp?
>>
>> No.
>>
>> > 3. Using a GIN-index, is there a way to use the index at all for
>> sorting?
>>
>> No.
>>
>> > 4. It doesn't seem like ts_rank uses the index for sorting either.
>>
>> Same reason.
>>
>> regards, tom lane
>>
>>
>> So it's basically impossible to use FTS/GIN with sorting on large
>> datasets?
>> Are there any plans to improve this situation?
>>
>
> I don't see why it would not be possible to create a new execution node
> type that does an index scan to obtain order (or just to satisfy an
> equality or range expression), and takes a bitmap (as produced by the
> FTS/GIN) to apply as a filter. But, I don't know of anyone planning on
> doing that.
>

Please, find bitmap filtering patch, which we developed several months ago,
but failed to find good use case :( Teodor is here now, so he could answer
the questions.

>
> Cheers,
>
> Jeff
>