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(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp <mailto:fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)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