Re: Accessing parameters of a prepared query inside an FDW

On Wednesday, February 14, 2024, Adam Fletcher <adamfblahblah(at)gmail(dot)com>
wrote:
>
>
> Is it possible to get the parameterized prepared query inside an FDW such
> that it can be prepared/bind'd/execute'd on the receiving end of the FDW?
>
> For example, if I `PREPARE stmt(int) AS SELECT * from fdwrapped_tbl where
> pk = $1;` then `execute stmt(1);` I want my FDW be aware that the query was
> prepared.
>

That isn’t how the separation of responsibilities works in PostgreSQL.
Execute is capable of producing a custom plan where instead of adding in
parameters and then planning around those unknowns the newly created plan
uses the supplied constants while planning.

I do suspect that if a generic plan is chosen you will see the expected
parse nodes and can thus build a generic access plan to your foreign server
accordingly.

You can control this for ease of testing via plan_cache_mode

https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-PLAN-CACHE-MODE

David J.