Thanks for the reply. There are two things I think I’ve been misunderstood:
1, the point is to do the rewrite without and before catalog access
2, I do want to push the join to the source and equally important pushing the where conditions there
Best regards, David
2014.02.13. dátummal, 21:22 időpontban Tom Lane <tgl@sss.pgh.pa.us> írta:
> David Beck <dbeck@starschema.net> writes:
>> I have table like data structures in the source system for the FDW I work on.
>> These tables are sometimes too big and the source system is able to filter and join them with limitations, thus it
isnot optimal to transfer the data to Postgres.
>> At the same time I want the users to think in terms of the original tables.
>
>> The idea is to rewrite the SQL queries like this:
>
>> “SELECT * FROM tableA a, tableB b WHERE a.id=b.id AND a.col1=1234 AND b.col2=987”
>
>> to:
>
>> “SELECT * FROM fdw_tableA_tableB ab WHERE ab.col1=1234 AND ab.col2=987”
>
> TBH this sounds like a spectacularly bad idea, especially in the place and
> way you propose to do it. You can't even do catalog access safely where
> you've put that hook, not to mention that there are many other places
> where queries can be submitted. But more generally, an FDW should not
> operate in the way you're describing.
>
> We do lack support for pushing joins to the foreign server, and that needs
> to be addressed; but we need to do it in the planner, not by kluging the
> query somewhere upstream of that.
>
> regards, tom lane
