Hi Zhenglong, I noticed that the [Windows CI job on CFBot](https://github.com/postgres/postgres-cfbot/actions/runs/41330725300/job/124920407235) failed with “The hosted runner lost communication with the server.”
I suggest checking the failure and, if it appears to be a runner issue, and requeuing the tests from the CommitFest page. Regards, Ziming ________________________________________ From: Keyerror Smart <[email protected]> Sent: Monday, October 12, 2026 13:44 To: Ziming Zhang Cc: PostgreSQL Hackers Subject: Re: [PATCH] Combine qual-based and NOT NULL proofs when reducing outer joins > I reviewed v1 of this patch. The approach looks sound to me. > > state->nullable_rels records whether a relation can be null-extended > within the subtree in general. If find_nonnullable_rels(all_quals) > proves that the relation cannot be an all-NULL row among the rows of > interest, then it must represent a real base-table row there, so its > table-level NOT NULL constraints can be used again. Hi Ziming, Thanks for taking the time to review and test this, and sorry for the slow reply -- I was away for a few weeks. Your summary is exactly the argument: nullable_rels answers "could this rel ever be null-extended in the subtree?", while find_nonnullable_rels over the collected quals answers the narrower question "could it be null-extended in a row that survives these quals?". Only the second question matters for the Vars we are trying to prove non-null, so the NOT NULL constraints can be trusted again for rels where the answer is no. > I tested the patch with an --enable-debug --enable-cassert build. The > core regression tests passed, and git diff --check reports no problems. > > I also compared patched and unpatched builds with a few additional > cases. The strict cases were reduced to Anti Join with unchanged > results, while a non-strict condition that allowed a lower > null-extended row to pass correctly retained the outer join. I also > checked the FULL JOIN case and did not find a result difference. Glad the non-strict and FULL JOIN cases held up on your side as well; those were the ones I was least sure I had covered. I just re-checked v1 against current master (36a56229765) and it still applies cleanly, so I am not posting a new version for now. Richard's recent changes in this area (ad4b80b6f49 and e28cf96e935) are both already included in the base I tested on. Thanks again, Zhenglong Li Ziming Zhang <[email protected]<mailto:[email protected]>> 于2026年9月21日周一 00:16写道： Hi Zhenglong, I reviewed v1 of this patch. The approach looks sound to me. state->nullable_rels records whether a relation can be null-extended within the subtree in general. If find_nonnullable_rels(all_quals) proves that the relation cannot be an all-NULL row among the rows of interest, then it must represent a real base-table row there, so its table-level NOT NULL constraints can be used again. The new proof only considers the quals already collected by forced_null_var_is_nonnullable(), so it does not appear to weaken the existing safety rules for outer-join reduction. I tested the patch with an --enable-debug --enable-cassert build. The core regression tests passed, and git diff --check reports no problems. I also compared patched and unpatched builds with a few additional cases. The strict cases were reduced to Anti Join with unchanged results, while a non-strict condition that allowed a lower null-extended row to pass correctly retained the outer join. I also checked the FULL JOIN case and did not find a result difference. I did not find any correctness or implementation issues. The patch looks good to me. Regards, Ziming ________________________________________ From: Keyerror Smart <[email protected]<mailto:[email protected]>> Sent: Tuesday, September 8, 2026 17:46 To: PostgreSQL Hackers Subject: [PATCH] Combine qual-based and NOT NULL proofs when reducing outer joins Hi hackers, reduce_outer_joins() can convert a LEFT or FULL join to an anti-join when an upper qual forces a Var from the nullable side to be NULL while that Var is provably non-null in every row of interest. There are two proof methods: quals that hold for all such rows (the subtree's safe quals, plus the join's own ON quals in the LEFT case) can prove specific Vars non-null, and a NOT NULL table constraint can prove a Var non-null unless its rel can be nulled by lower-level outer joins within the subtree. Previously the two methods did not combine: once a rel was found nullable within the subtree, its NOT NULL constraints were ignored outright. But if the collected quals are strict for the rel, it cannot have been null-extended in any row of interest, so its NOT NULL constraints do apply to those rows after all. Compute find_nonnullable_rels() over the quals forced_null_var_is_nonnullable() already collects, and have forced_null_var_is_attnotnull() trust NOT NULL constraints of rels so proven. For example, with Q.ts declared NOT NULL, this query's outer join can now be reduced to an anti-join: the upper ON clause Q.f = 1 is strict for Q, so Q cannot be null-extended in any matching row, leaving the upper join's own null-extension as the only way to satisfy the WHERE clause. SELECT * FROM R LEFT JOIN (S LEFT JOIN Q ON S.c = Q.e) ON R.a = S.c AND Q.f = 1 WHERE Q.ts IS NULL; The same reasoning applies at a FULL join, where safe quals within one input can prove a rel non-extended in every row that input emits. Patch atrtached. Regards, Zhenglong Li
