Re: Odd system-column handling in postgres_fdw join pushdown patch

On 2016/03/23 13:44, Ashutosh Bapat wrote:

An FDW can choose not to use those functions, so I don't see a
connection between scan list having simple Vars and existence of those
functions (actually a single one). But having those function would
minimize the code that each FDW has to write, in case they want those
functions. E.g. we have to translate Var::varno to tableoid in case
that's requested by pulling RTE and then getting oid out from there. If
that functionality is available in the core, 1. the code is not
duplicated 2. every FDW will get the same tableoid. Similarly for the
other columns.

OK.  Then, I'd like to propose a function that would create interger Lists of indexes of tableoids, xids and cids plus

an OID List of these tableoids,

in a given fdw_scan_tlist, on the assumption that each expression in the fdw_scan_tlist is a simple Var. 

I'd also like to propose another function that would fill system columns using these Lists when creating a scan tuple.