I wrote:
> I think possibly the best answer is to revert 8ed3f11bb. We could
> think about some compromise solution like merging the projections
> only for aggregates without FILTER. But that would require two
> code paths through the relevant functions in nodeAgg.c, which would
> be a substantial maintenance burden; and the extra branches required
> means that this would be a net negative for performance in the
> simplest case with only one aggregate.
Hmm ... on closer inspection, the only performance-critical place
where this matters is advance_aggregates, and that already has a check
for whether the particular aggregate has a filter. So we could do
something like
/* Skip anything FILTERed out */
if (filter)
{
// existing code to eval/check filter expr
+
+ /* Now it's safe to evaluate this agg's arguments */
+ slot = ExecProject(pertrans->argproj);
}
+ else
+ slot = aggstate->evalslot;
which seems like a pretty minimal extra cost for the normal case
with no filter.
Let me see what I can make of that ...
regards, tom lane
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