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Re: Accessing parameters of a prepared query inside an FDW

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On Wednesday, February 14, 2024, Adam Fletcher <adamfblahblah@xxxxxxxxx> 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.


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