Re: RFC: planner statistics in 7.2

At 21:14 19/04/01 -0400, Tom Lane wrote:
>Philip Warner <pjw(at)rhyme(dot)com(dot)au> writes:
>> I'm not sure you want to know how well sorted it is in general, but you do
>> want to know the expected cost in IOs of reading all records from a given
>> index node, so you can more accurately estimate indexscan costs. AFAICS it
>> does not require that the entire table be sorted. So checking the pointers
>> on the index nodes gives an idea of clustering.
>
>But you don't really need to look at the index (if it even exists
>at the time you do the ANALYZE). The extent to which the data is
>ordered in the table is a property of the table, not the index.

But the value (and cost) of using a specific index in an indexscan depends
on that index (or am I missing something?).

----------------------------------------------------------------
Philip Warner | __---_____
Albatross Consulting Pty. Ltd. |----/ - \
(A.B.N. 75 008 659 498) | /(@) ______---_
Tel: (+61) 0500 83 82 81 | _________ \
Fax: (+61) 0500 83 82 82 | ___________ |
Http://www.rhyme.com.au | / \|
| --________--
PGP key available upon request, | /
and from pgp5.ai.mit.edu:11371 |/