planner: remove redundant branches in the OR list | tidb-test=pr/2470 #58962
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| Original file line number | Diff line number | Diff line change |
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@@ -186,6 +186,7 @@ func splitCNF(conditions []expression.Expression) []expression.Expression { | |
| func applyPredicateSimplification(sctx base.PlanContext, predicates []expression.Expression) []expression.Expression { | ||
| simplifiedPredicate := shortCircuitLogicalConstants(sctx, predicates) | ||
| simplifiedPredicate = mergeInAndNotEQLists(sctx, simplifiedPredicate) | ||
| removeRedundantORBranch(sctx, simplifiedPredicate) | ||
| pruneEmptyORBranches(sctx, simplifiedPredicate) | ||
| simplifiedPredicate = splitCNF(simplifiedPredicate) | ||
| return simplifiedPredicate | ||
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@@ -424,6 +425,51 @@ func shortCircuitLogicalConstants(sctx base.PlanContext, predicates []expression | |
| return finalResult | ||
| } | ||
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| // removeRedundantORBranch recursively iterates over a list of predicates, try to find OR lists and remove redundant in | ||
| // each OR list. | ||
| // It modifies the input slice in place. | ||
| func removeRedundantORBranch(sctx base.PlanContext, predicates []expression.Expression) { | ||
| for i, predicate := range predicates { | ||
| predicates[i] = recursiveRemoveRedundantORBranch(sctx, predicate) | ||
| } | ||
| } | ||
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| func recursiveRemoveRedundantORBranch(sctx base.PlanContext, predicate expression.Expression) expression.Expression { | ||
| _, tp := FindPredicateType(sctx, predicate) | ||
| if tp != orPredicate { | ||
|
There was a problem hiding this comment. This is a recursive function (indirectly through removeRedundantORBranch). If you intend to cover the And case (like the code in the function) then you just need a general logic for OR AND lists. There was a problem hiding this comment. I didn't intend to cover the AND case (since that's already covered by other existing logic), I want to handle OR lists nested in another AND list. |
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| return predicate | ||
| } | ||
| orFunc := predicate.(*expression.ScalarFunction) | ||
| orList := expression.SplitDNFItems(orFunc) | ||
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| dedupMap := make(map[string]struct{}, len(orList)) | ||
| newORList := make([]expression.Expression, 0, len(orList)) | ||
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| for _, orItem := range orList { | ||
| _, tp := FindPredicateType(sctx, orItem) | ||
| // 1. If it's an AND predicate, we recursively call removeRedundantORBranch() on it. | ||
| if tp == andPredicate { | ||
| andFunc := orItem.(*expression.ScalarFunction) | ||
| andList := expression.SplitCNFItems(andFunc) | ||
| removeRedundantORBranch(sctx, andList) | ||
| newORList = append(newORList, expression.ComposeCNFCondition(sctx.GetExprCtx(), andList...)) | ||
| } else { | ||
| // 2. Otherwise, we check if it's a duplicate predicate by checking HashCode(). | ||
| hashCode := string(orItem.HashCode()) | ||
| // 2-1. If it's not a duplicate, we need to keep this predicate. | ||
| if _, ok := dedupMap[hashCode]; !ok { | ||
| dedupMap[hashCode] = struct{}{} | ||
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There was a problem hiding this comment. Minor: the value of the map can be anything and may be just a simple constant like True. There was a problem hiding this comment. Technically, yes. But I think using |
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| newORList = append(newORList, orItem) | ||
| } else if expression.IsMutableEffectsExpr(orItem) { | ||
| // 2-2. If it's a duplicate, but it's nondeterministic or has side effects, we also need to keep it. | ||
| newORList = append(newORList, orItem) | ||
| } | ||
| // 2-3. Otherwise, we remove it. | ||
| } | ||
| } | ||
| return expression.ComposeDNFCondition(sctx.GetExprCtx(), newORList...) | ||
| } | ||
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| // Name implements base.LogicalOptRule.<1st> interface. | ||
| func (*PredicateSimplification) Name() string { | ||
| return "predicate_simplification" | ||
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Any reason of the order of the sub-rule?
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There are no strong reasons. Actually, after I put this new sub-rule in a different order, the new test cases don't have any changes.
I have several minor considerations though:
mergeInAndNotEQLists()simplifies the predicates by merging some of them, i.e., constructing some new expressions. Probably there will be new redundant expressions after that sub-rule, so put the new sub-rule after it might be a good idea.pruneEmptyORBranches()just removes useless OR branches, and should not produce new redundant expressions. So probably it's useless to put the new sub-rule after it.