Re: The planner chooses seqscan+sort when there is an

am  03.05.2006, um 20:20:55 +0200 mailte Florian G. Pflug folgendes:
> >of the index scan ? The table is quite big, might be possible. I still
> >wonder why would be seqscan+sort faster than index scan... the sort will
> >for sure have to write to disk too given the size of the table...
>
> When using an indexscan, postgres will read the actual rows in index-order,
> rathen then in the order they appear on-disk.
> For 200 million rows this means doing at least 200 million
> disk seeks. Assuming that each seek takes just 1ms, thats
> still amount to 200.000 seconds.

Yepp, it is much cheaper to read the table seq and order later.


Andreas
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