Re: Use %u to print user mapping's umid and userid

On 2016/05/11 18:03, Ashutosh Bapat wrote:
> On Wed, May 11, 2016 at 1:34 PM, Etsuro Fujita
> <fujita.etsuro@lab.ntt.co.jp <mailto:fujita.etsuro@lab.ntt.co.jp>> wrote:

>     On 2016/05/11 16:49, Ashutosh Bapat wrote:
>
>         The patch is calculating user mapping when it's readily available
>         through RelOptInfo::fdw_private. That incurs a catalog lookup
>         unnecessarily. Instead, can we add new function makeOid, oidVal
>         on the
>         lines of makeInteger and intVal to store and retrieve an OID
>         resp. and
>         also corresponding print function? It might be helpful in future.

>     That might be an idea, but is the overhead in that re-calculation so
>     large?

> 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?

Best regards,
Etsuro Fujita