Re: Additional improvements to extended statistics

On Mon, Mar 09, 2020 at 01:01:57AM +0100, Tomas Vondra wrote:
>On Sun, Mar 08, 2020 at 07:17:10PM +0000, Dean Rasheed wrote:
>>On Fri, 6 Mar 2020 at 12:58, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
>>>
>>>Here is a rebased version of this patch series. I've polished the first
>>>two parts a bit - estimation of OR clauses and (Var op Var) clauses.
>>>
>>
>>Hi,
>>
>>I've been looking over the first patch (OR list support). It mostly
>>looks reasonable to me, except there's a problem with the way
>>statext_mcv_clauselist_selectivity() combines multiple stat_sel values
>>into the final result -- in the OR case, it needs to start with sel =
>>0, and then apply the OR formula to factor in each new estimate. I.e.,
>>this isn't right for an OR list:
>>
>>       /* Factor the estimate from this MCV to the oveall estimate. */
>>       sel *= stat_sel;
>>
>>(Oh and there's a typo in that comment: s/oveall/overall/).
>>
>>For example, with the regression test data, this isn't estimated well:
>>
>> SELECT * FROM mcv_lists_multi WHERE a = 0 OR b = 0 OR c = 0 OR d = 0;
>>
>>Similarly, if no extended stats can be applied it needs to return 0
>>not 1, for example this query on the test data:
>>
>> SELECT * FROM mcv_lists WHERE a = 1 OR a = 2 OR d IS NOT NULL;
>>
>
>Ah, right. Thanks for noticing this. Attaches is an updated patch series
>with parts 0002 and 0003 adding tests demonstrating the issue and then
>fixing it (both shall be merged to 0001).
>

One day I won't forget to actually attach the files ...


regards

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