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12ec16d11c
The path we wish to reparameterize is not a standalone object: in particular, it implicitly references baserestrictinfo clauses in the associated RelOptInfo, and if it's a SampleScan path then there is also the TableSampleClause in the RTE to worry about. Both of those could contain lateral references to the join partner relation, which would need to be modified to refer to its child. Since we aren't doing that, affected queries can give wrong answers, or odd failures such as "variable not found in subplan target list", or executor crashes. But we can't just summarily modify those expressions, because they are shared with other paths for the rel. We'd break things if we modify them and then end up using some non-partitioned-join path. In HEAD, we plan to fix this by postponing reparameterization until create_plan(), when we know that those other paths are no longer of interest, and then adjusting those expressions along with the ones in the path itself. That seems like too big a change for stable branches however. In the back branches, let's just detect whether any troublesome lateral references actually exist in those expressions, and fail reparameterization if so. This will result in not performing a partitioned join in such cases. Given the lack of field complaints, nobody's likely to miss the optimization. Report and patch by Richard Guo. Apply to 12-16 only, since the intended fix for HEAD looks quite different. We're not quite ready to push the HEAD fix, but with back-branch releases coming up soon, it seems wise to get this stopgap fix in place there. Discussion: https://postgr.es/m/CAMbWs496+N=UAjOc=rcD3P7B6oJe4rZw08e_TZRUsWbPxZW3Tw@mail.gmail.com |
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