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069d0ff022
If we intend to generate a Memoize node on top of a path, we need cache keys of some sort. Currently we search for the cache keys in the parameterized clauses of the path as well as the lateral_vars of its parent. However, it turns out that this is not sufficient because there might be lateral references derived from PlaceHolderVars, which we fail to take into consideration. This oversight can cause us to miss opportunities to utilize the Memoize node. Moreover, in some plans, failing to recognize all the cache keys could result in performance regressions. This is because without identifying all the cache keys, we would need to purge the entire cache every time we get a new outer tuple during execution. This patch fixes this issue by extracting lateral Vars from within PlaceHolderVars and subsequently including them in the cache keys. In passing, this patch also includes a comment clarifying that Memoize nodes are currently not added on top of join relation paths. This explains why this patch only considers PlaceHolderVars that are due to be evaluated at baserels. Author: Richard Guo Reviewed-by: Tom Lane, David Rowley, Andrei Lepikhov Discussion: https://postgr.es/m/CAMbWs48jLxn0pAPZpJ50EThZ569Xrw+=4Ac3QvkpQvNszbeoNg@mail.gmail.com