Re: PATCH: index-only scans with partial indexes

Hello!

On 09/30/2015 10:29 AM, Kyotaro HORIGUCHI wrote:

> By the way your comment for indexrinfos is as following,
>
>> * 'indexrinfos' is a list of RestrictInfo nodes from the query's WHERE
>> * or JOIN conditions, excluding those implied by the index predicate
>> * (if the index is not partial, the list includes all restriction clauses).
>
> But the v4 patch instead leaves it empty for non-partial
> indexes:) I prefer to follow this comment because looking the
> condition (index->indpred != NIL) for such purpose in
> build_index_paths is somewhat uneasy for me. But I don't insist
> on that if you choose to avoid useless memory and clock
> consumption to construct a list which is not so meaningful for
> non-partial indexes (it is almost all cases).

Good point. I think we may simply point indexrinfos to the existing list 
of restrictions in that case - we don't need to copy it. So no 
additional memory / CPU consumption, and it should make the code working 
with it a bit simpler.

>
> The following comment in match_clause_to_index does not need to be a
> 'XXX' comment. What made you to feel to do so? (I rather feel that it
> is not necessary at all.)

I agree that it may not be really necessary. I added the comment because 
initially I've made the check inside the for loop and then spent some 
time investigating why it's not working as expected.

>
>> * XXX We must do this before trying to match the index to index
>> *     columns, because the index predicates may use columns not
>> *     used in the index itself.
>
> Anyway some description on rclauses should be added in the
> comment for match_clause_to_index, instead of the comments
> currently added *within* the function.

OK, will do.


kind regards

-- 
Tomas Vondra                   http://www.2ndQuadrant.com/
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