On Thu, Jun 22, 2017 at 11:12 AM, Amit Langote
<Langote_Amit_f8@lab.ntt.co.jp> wrote:
> On 2017/06/22 10:01, Michael Paquier wrote:
>> #3 implies that the index AM logic is implemented in the table
>> AM. Not saying that it is not useful, but it does not feel natural to
>> have the planner request for a sequential scan, just to have the table
>> AM secretly do some kind of index/skipping scan.
>
> I had read a relevant comment on a pluggable storage thread awhile back
> [1]. In short, the comment was that the planner should be able to get
> some intelligence, via some API, from the heap storage implementation
> about the latter's access cost characteristics. The storage should
> provide accurate-enough cost information to the planner when such a
> request is made by, say, cost_seqscan(), so that the planner can make
> appropriate choice. If two tables containing the same number of rows (and
> the same size in bytes, perhaps) use different storage implementations,
> then, planner's cost parameters remaining same, cost_seqscan() will end up
> calculating different costs for the two tables. Perhaps, SeqScan would be
> chosen for one table but not the another based on that.
Yeah, I agree that the costing part needs some clear attention and
thoughts, and the gains are absolutely huge with the correct
interface. That could be done in a later step though.
--
Michael