Re: Index scan vs indexonly scan method

> The background on index-only scans:
>
> https://wiki.postgresql.org/wiki/What%27s_new_in_PostgreSQL_9.2#Index-only_scans
>
>
> In either case(index, index-only) the index has to be scanned. The
> difference is where the data is pulled from. In the index-only scan
> the query still needs to consult the visibility map to determine
> whether the tuple pointed to by the index entry is visible. I would
> say that in the limit 1 case the planner determines it is just as easy
> to check and pull the data from the actual tuple as to to check the
> visibility map. In the limit 100 case it becomes more cost effective
> to use the visibility map and pull data directly from the index data.
>
>
Thank you for your answer

Enrico


--
That's one small step for man; one giant leap for mankind

Enrico Pirozzi
Tel.  +39 0861 1855771 - Mob.+39 328 4164437 - Fax  +39 0861 1850310
http://www.pgtraining.com <http://www.pgtraining.com-> -
info@pgtraining.com
www.enricopirozzi.info - info@enricopirozzi.info
PEC: enrico.pirozzi@pec.it
Skype sscotty71 - Gtalk sscotty71@gmail.com