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

On Wed, Mar 16, 2016 at 6:53 AM, Andreas Joseph Krogh <andreas@visena.com> wrote:

På onsdag 16. mars 2016 kl. 14:37:27, skrev Tom Lane <tgl@sss.pgh.pa.us>:

Andreas Joseph Krogh <andreas@visena.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.

Cheers,

Jeff