Re: [PATCH] Negative Transition Aggregate Functions (WIP)

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От David Rowley
Тема Re: [PATCH] Negative Transition Aggregate Functions (WIP)
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Msg-id CAApHDvpCbho2rE4jsAPRUh5hBpM8hA+PwhRqe=g58zpj-KGx7Q@mail.gmail.com
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Ответ на Re: [PATCH] Negative Transition Aggregate Functions (WIP)  (David Rowley <dgrowleyml@gmail.com>)
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On Sun, Jan 19, 2014 at 5:27 PM, David Rowley <dgrowleyml@gmail.com> wrote:

>> It's probably far more worth it for the bool and/or aggregates. We could just
>> keep track of the values aggregated and the count of values as "true" and return
>> true if those are the same in the case of "AND", then check the true count
>> is > 0 in the case of "OR". I'd feel more strongly to go and do that if I'd
>> actually ever used those aggregates for anything.

That, OTOH, would be worthwhile I think. I'll go do that, though probably
not today. I hope to get to it sometime tomorrow.

I've commited a patch to the github repo to do this.
but I'm not sure if we can keep it as I had to remove the sort op as I explained above. 


I think I'm going to have to revert the patch which implements the inverse transition function for bool_and and bool_or.
I tested on an instance of 9.3.2 and the following queries use index scans.

create table booltest (b boolean not null);
insert into booltest (b) select false from generate_series(1,20000) g(n);
insert into booltest (b) values(true);

create index booltest_b_idx ON booltest(b);
vacuum analyze booltest;

explain select bool_or(b) from booltest;
explain select bool_and(b) from booltest;

I'm guessing there is no way to have an internal state type on the aggregate and a sort operator on the aggregate.

I wonder if it is worth creating naive inverse transition functions similar to max()'s and min()'s inverse transition functions. I guess on average they've got about a 50% chance of being used and likely for some work loads it would be a win.

What's your thoughts?

Regards
David Rowley
 

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