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Commit5748f3a

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Improve predtest.c's internal docs, and enhance its functionality a bit.
Commitb08df9c left things rather poorly documented as far as theexact semantics of "clause_is_check" mode went. Also, that mode didnot really work correctly for predicate_refuted_by; although given thelack of specification as to what it should do, as well as the lackof any actual use-case, that's perhaps not surprising.Rename "clause_is_check" to "weak" proof mode, and provide specificationsfor what it should do. I defined weak refutation as meaning "truth of Aimplies non-truth of B", which makes it possible to use the mode in thepart of relation_excluded_by_constraints that checks for mutuallycontradictory WHERE clauses. Fix up several places that did things wrongfor that definition. (As far as I can see, these errors would only leadto failure-to-prove, not incorrect claims of proof, making them notserious bugs even aside from the fact that v10 contains no use of thismode. So there seems no need for back-patching.)In addition, teach predicate_refuted_by_recurse that it can usepredicate_implied_by_recurse after all when processing a strong NOT-clause,so long as it asks for the correct proof strength. This is an optimizationthat could have been included in commitb08df9c, but wasn't.Also, simplify and generalize the logic that checks for whether nullness ofthe argument of IS [NOT] NULL would force overall nullness of the predicateor clause. (This results in a change in the partition_prune test's output,as it is now able to prune an all-nulls partition that it did not recognizebefore.)In passing, in PartConstraintImpliedByRelConstraint, remove bogusconversion of the constraint list to explicit-AND form and then right backagain; that accomplished nothing except forcing a useless extra level ofrecursion inside predicate_implied_by.Discussion:https://postgr.es/m/5983.1520487191@sss.pgh.pa.us
1 parenta63c327 commit5748f3a

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8 files changed

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‎src/backend/commands/tablecmds.c

Lines changed: 13 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -13651,10 +13651,11 @@ ComputePartitionAttrs(Relation rel, List *partParams, AttrNumber *partattrs,
1365113651

1365213652
/*
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* PartConstraintImpliedByRelConstraint
13654-
*Does scanrel's existing constraints imply the partition constraint?
13654+
*Do scanrel's existing constraints imply the partition constraint?
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*
13656-
* Existing constraints includes its check constraints and column-level
13657-
* NOT NULL constraints and partConstraint describes the partition constraint.
13656+
* "Existing constraints" include its check constraints and column-level
13657+
* NOT NULL constraints. partConstraint describes the partition constraint,
13658+
* in implicit-AND form.
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*/
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bool
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PartConstraintImpliedByRelConstraint(Relationscanrel,
@@ -13724,10 +13725,15 @@ PartConstraintImpliedByRelConstraint(Relation scanrel,
1372413725
make_ands_implicit((Expr*)cexpr));
1372513726
}
1372613727

13727-
if (existConstraint!=NIL)
13728-
existConstraint=list_make1(make_ands_explicit(existConstraint));
13729-
13730-
/* And away we go ... */
13728+
/*
13729+
* Try to make the proof. Since we are comparing CHECK constraints, we
13730+
* need to use weak implication, i.e., we assume existConstraint is
13731+
* not-false and try to prove the same for partConstraint.
13732+
*
13733+
* Note that predicate_implied_by assumes its first argument is known
13734+
* immutable. That should always be true for partition constraints, so we
13735+
* don't test it here.
13736+
*/
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returnpredicate_implied_by(partConstraint,existConstraint, true);
1373213738
}
1373313739

‎src/backend/optimizer/util/plancat.c

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1421,7 +1421,11 @@ relation_excluded_by_constraints(PlannerInfo *root,
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safe_restrictions=lappend(safe_restrictions,rinfo->clause);
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}
14231423

1424-
if (predicate_refuted_by(safe_restrictions,safe_restrictions, false))
1424+
/*
1425+
* We can use weak refutation here, since we're comparing restriction
1426+
* clauses with restriction clauses.
1427+
*/
1428+
if (predicate_refuted_by(safe_restrictions,safe_restrictions, true))
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return true;
14261430

14271431
/*
@@ -1469,6 +1473,9 @@ relation_excluded_by_constraints(PlannerInfo *root,
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* an obvious optimization. Some of the clauses might be OR clauses that
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* have volatile and nonvolatile subclauses, and it's OK to make
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* deductions with the nonvolatile parts.
1476+
*
1477+
* We need strong refutation because we have to prove that the constraints
1478+
* would yield false, not just NULL.
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*/
14731480
if (predicate_refuted_by(safe_constraints,rel->baserestrictinfo, false))
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return true;

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