Re: asynchronous and vectorized execution

On Wed, May 11, 2016 at 3:52 AM, Andres Freund <andres@anarazel.de> wrote:
> On 2016-05-11 03:20:12 +0300, Ants Aasma wrote:
>> On Tue, May 10, 2016 at 7:56 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> > On Mon, May 9, 2016 at 8:34 PM, David Rowley
>> > <david.rowley@2ndquadrant.com> wrote:
>> > I don't have any at the moment, but I'm not keen on hundreds of new
>> > vector functions that can all have bugs or behavior differences versus
>> > the unvectorized versions of the same code.  That's a substantial tax
>> > on future development.  I think it's important to understand what
>> > sorts of queries we are targeting here.  KaiGai's GPU-acceleration
>> > stuff does great on queries with complex WHERE clauses, but most
>> > people don't care not only because it's out-of-core but because who
>> > actually looks for the records where (a + b) % c > (d + e) * f / g?
>> > This seems like it has the same issue.  If we can speed up common
>> > queries people are actually likely to run, OK, that's interesting.
>>
>> I have seen pretty complex expressions in the projection and
>> aggregation. Couple dozen SUM(CASE WHEN a THEN b*c ELSE MIN(d,e)*f
>> END) type of expressions. In critical places had to replace them with
>> a C coded function that processed a row at a time to avoid the
>> executor dispatch overhead.
>
> I've seen that as well, but Was it the actual fmgr indirection causing
> the overhead, or was it ExecQual/ExecMakeFunctionResultNoSets et al?

I don't remember what the exact profile looked like, but IIRC it was
mostly Exec* stuff with advance_aggregates also up there.

Regards,
Ants Aasma