Re: Accessing parameters of a prepared query inside an FDW - Mailing list pgsql-general

From Adam Fletcher
Subject Re: Accessing parameters of a prepared query inside an FDW
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Msg-id CAMfJBeCgWRjWcXYf7cgSZA88RxxtTqxgY1r_wr0wjnzg3UYMyA@mail.gmail.com
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In response to Re: Accessing parameters of a prepared query inside an FDW  ("David G. Johnston" <david.g.johnston@gmail.com>)
List pgsql-general


On Wed, Feb 14, 2024 at 7:43 PM David G. Johnston <david.g.johnston@gmail.com> wrote:
On Wednesday, February 14, 2024, Adam Fletcher <adamfblahblah@gmail.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



Thanks David, this solved my problem - here’s the reasons I asked: 
https://github.com/EnterpriseDB/mysql_fdw/pull/293 - this adds parameter forwarding to the MySQL FDW. 

Thanks again!

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