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Now that CTEs are no longer optimization fences in recent versions of Postgres, is there a way to somehow manually declare an optimization fence around a certain region of the query?

I've had similar problems in Snowflake with the query planner taking a bad path, and no obvious way to hint otherwise.

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Functions are hard barriers for optimization and I don't see that changing any time soon.

Which goes even so far that EXPLAIN doesn't work on them and you just get a black box of "Function call to ..." in the execution plan.

Using auto_explain is the only workaround known to me for that.

But that's not the case when functions are inlined.

Interesting. I've never seen this though. I guess that only happens for simple cases?

WITH MATERIALIZED restores the fence.

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