On 01/19/2017 04:09 AM, Ashutosh Bapat wrote:
On Thu, Jan 19, 2017 at 12:02 AM, Robert Haas <robertmh...@gmail.com> wrote:
On Tue, Jan 17, 2017 at 11:33 PM, Ashutosh Bapat
Also, the point is naming that kind of function as aggtransmultifn
would mean that it's always supposed to multiply, which isn't true for
all aggregates.
TransValue * integer = newTransValue is well-defined for any
aggregate. It's the result of aggregating that TransValue with itself
a number of times defined by the integer. And that might well be
significantly faster than using aggcombinefn many times. On the other
hand, how many queries just sit there are re-aggregate the same
TransValues over and over again? I am having trouble wrapping my head
around that part of this.
Not all aggregates have TransValue * integer = newTransValue
behaviour. Example is array_agg() or string_agg() has "TransValue
concatenated integer time" behaviour. Or an aggregate "multiplying"
values across rows will have TransValue (raised to) integer behaviour.
Labelling all of those as "multi" doesn't look good.
All aggregates that have (or can have) a combine function have it,
because in the worst case you can simply implement it by calling the
combine function repeatedly.
Also, if you treat the combine function as "+" then the "multiply"
function is exactly what "*" is expected to do. So I find the naming
quite appropriate, actually.
But I think naming of the function is not the most important aspect of
the patch, I believe. In the worst case, we can do s/multi/whatever/
sometime later.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
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