Re: review: Non-recursive processing of AND/OR lists

On Mon, Jul 15, 2013 at 12:45 AM, Gurjeet Singh <gurjeet@singh.im> wrote:
> Agreed that there's overhead in allocating list items, but is it more
> overhead than pushing functions on the call stack? Not sure, so I leave it
> to others who understand such things better than I do.

If you think that a palloc can ever be cheaper that pushing a frame on
the callstack, you're wrong.  palloc is not some kind of an atomic
primitive.  It's implemented by the AllocSetAlloc function, and you're
going to have to push that function on the call stack, too, in order
to run it.

My main point here is that if the user writes a = 1 and b = 1 and c =
1 and d = 1, they're not going to end up with a bushy tree.  They're
going to end up with a tree that's only deep in one direction (left, I
guess) and that's the case we might want to consider optimizing.  To
obtain a bushy tree, they're going to have to write a  = 1 and (b = 1
and c = 1) and d = 1, or something like that, and I don't see why we
should stress out about that case.  It will be rare in practice.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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