Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> writes:
> On 2016/05/11 18:03, Ashutosh Bapat wrote:
>> A call to GetForeignTable would incur a catalog lookup which means a
>> catalog table/index scan if corresponding entry is not in the cache.
>> This is followed by GetUserMapping() which is another catalog access.
>> That's bound to be expensive than an makeOid(), oidVal() call.
> Right, but such lookups have been incurred at the planning time (ie,
> build_simple_rel), and corresponding entries would be in the cache. So,
> the overhead in that recalculation at the execution time would be not
> that large in practice. No?
It's a mistake to assume that execution immediately follows planning.
Having said that, I wonder whether you should be thinking less about
performance and more about correctness. Is a user mapping lookup done
at plan time still valid at execution, and if so what ensures that?
regards, tom lane