Disallow DuckDB execution inside functions #764
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pg_duckdb changes result types of queries at the planning stage. This is needed for pg_duckdb to function correctly. However, Postgres code is sometimes not written with this in mind. One such case is sql functions, as reported in #749. There it causes a crash, because Postgres expects a different type to be returned by the function than what is actually returned. As far as I can tell there is no easy way of fixing this, apart from changing Postgres to learn how to deal with this. I'll open issue/patch to Postgres for this at some point in the near future. For now, we simply start disallowing all DuckDB execution inside functions. That is quite a shame because using DuckDB execution in functions works fine in many other cases. Sadly, I cannot think of a way to only disallow the crashing cases. Since a very important part of pg_duckdb 1.0 is stability, it seems better to err on the side of caution and disable this feature for now and stabilize it in a future release.
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Y--
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May 7, 2025
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Co-authored-by: Y. <y.lemaout@gmail.com>
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JelteF
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Aug 15, 2025
DuckDB execution inside functions was disallowed in #764 for good reason However, some users depend on running analytics with pg_duckdb inside functions Given that (1) the problematic cases are rare, and (2) pg_duckdb is mostly used for read queries, failures are limited to crashing the current session and can be recovered by restarting the session without data loss. This change introduces an unsafe GUC to restore this capability for users who need it
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pg_duckdb changes result types of queries at the planning stage. This is needed for pg_duckdb to function correctly. However, Postgres code is sometimes not written with this in mind. One such case is sql functions, as reported in #749. There it causes a crash, because Postgres expects a different type to be returned by the function than what is actually returned.
As far as I can tell there is no easy way of fixing this, apart from changing Postgres to learn how to deal with this. I'll open issue/patch to Postgres for this at some point in the near future.
For now, we simply start disallowing all DuckDB execution inside functions. That is quite a shame because using DuckDB execution in functions works fine in many other cases. Sadly, I cannot think of a way to only disallow the crashing cases. Since a very important part of pg_duckdb 1.0 is stability, it seems better to err on the side of caution and disable this feature for now and stabilize it in a future release.
Fixes #749