Dear hackers,
Do you think there would be any use for an aggregate which returns an
array of the aggregated (usually simple) type? Has this already been
done by anyone? I looked at the source and noticed that for each
inserted item, the array utility functions perform a deep copy of the
entire array (plus a reallocation). Normally, this is no big deal, but
if executed in the query stage, it could be kind of slow.
What exactly have you looked at? In current cvs there is array_append and array_cat. There *was* array_accum, but that was yanked due to an objection that it was redundant with the other two.
There is a contrib (intagg) that avoids the deep copy by passing pointers as integers, but I don't think that would be accepted as a builtin solution. I've considered maybe using a hash table to register valid pointers, but have not thought too hard about it yet. In any case it won't happen for 7.4.
BTW, I tried array_accum() (which is not really much different than array_append()) with groups of about 10,000 elements and feeding the array into a plr final function for a mean calculation. It was for sure slow compared to a native AVG() aggregate, but it wasn't that bad either. I don't remember the specifics, but it would be easy enough to try it out for yourself.
I also noticed that null values inside is an item on the todo list. Is anybody
currently working on this?
No one is currently working on it that I'm aware of, but I was considering working on it for 7.5
Joe
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