Re: PassDownLimitBound for ForeignScan/CustomScan [take-2]

On Tue, Nov 8, 2016 at 6:54 AM, Jeevan Chalke
<jeevan(dot)chalke(at)enterprisedb(dot)com> wrote:
> 1. ps_numTuples is declared as long, however offset and count members in
> LimitState struct and bound member in SortState struct is int64. However
> long on 32 bit machine may be 32 bits and thus I think tuples_needed which
> is long may have overflow hazards as it may store int64 + int64. I think
> ps_numTuples should be int64.

I suggested long originally because that's what ExecutorRun() was
using at the time. It seems that it got changed to uint64 in
23a27b039d94ba359286694831eafe03cd970eef, so I guess we should
probably use uint64.

> 2. Robert suggested following in the previous discussion:
> "For example, suppose we add a new PlanState member "long
> numTuples" where 0 means that the number of tuples that will be needed
> is unknown (so that most node types need not initialize it), a
> positive value is an upper bound on the number of tuples that will be
> fetched, and -1 means that it is known for certain that we will need
> all of the tuples."
>
> We should have 0 for the default case so that we don't need to initialize it
> at most of the places. But I see many such changes in the patch. I think
> this is not possible here since 0 can be a legal user provided value which
> cannot be set as a default (default is all rows).
>
> However do you think, can we avoid that? Is there any other way so that we
> don't need every node having ps_numTuples to be set explicitly?

+1.

--
Robert Haas
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