Allow self-joining of Polars lazyframes#466
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evertlammerts merged 1 commit intoMay 19, 2026
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Fixes #452
This makes sure that Polars' CSE wraps the lazyframe in a
CACHE[...]in its plan. This way, the lazyframe will only be consumed once.We've seen this reported more often. The issue with joining a streaming result against itself is that a result can only be consumed once. One workaround is using multiple connections, but this only works if duckdb comes up with a query plan where a result is not referenced against itself.
As it turns out, Polars allows I/O plugins to register with
is_pure, and Polars will de-duplicate them. Afaict, there's not really any downside. I don't see why anybody would want to treat a streaming result as not-pure, or what that would mean. I guess we'll see if that assumption will pass the test of time.