ES|QL: Remove redundant sorts from execution plan #121156
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| pr: 121156 | ||
| summary: Remove redundant sorts from execution plan | ||
| area: ES|QL | ||
| type: bug | ||
| issues: [] |
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| /* | ||
| * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one | ||
| * or more contributor license agreements. Licensed under the Elastic License | ||
| * 2.0; you may not use this file except in compliance with the Elastic License | ||
| * 2.0. | ||
| */ | ||
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| package org.elasticsearch.xpack.esql.optimizer.rules.logical; | ||
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| import org.elasticsearch.xpack.esql.plan.logical.Aggregate; | ||
| import org.elasticsearch.xpack.esql.plan.logical.LogicalPlan; | ||
| import org.elasticsearch.xpack.esql.plan.logical.OrderBy; | ||
| import org.elasticsearch.xpack.esql.plan.logical.SortAware; | ||
| import org.elasticsearch.xpack.esql.plan.logical.TopN; | ||
| import org.elasticsearch.xpack.esql.plan.logical.UnaryPlan; | ||
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| import java.util.ArrayDeque; | ||
| import java.util.Deque; | ||
| import java.util.IdentityHashMap; | ||
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| /** | ||
| * SORT cannot be executed without a LIMIT, as ES|QL doesn't support unbounded sort (yet). | ||
| * <p> | ||
| * The planner tries to push down LIMIT and transform all the unbounded sorts into a TopN. | ||
| * In some cases it's not possible though, eg. | ||
| * <p> | ||
| * from test | sort x | lookup join lookup on x | sort y | ||
| * <p> | ||
| * from test | sort x | mv_expand x | sort y | ||
| * <p> | ||
| * "sort y" will become a TopN due to the addition of the default Limit, but "sort x" will remain unbounded, | ||
| * so the query could not be executed. | ||
| * <p> | ||
| * In most cases though, following commands can make the previous SORTs redundant, | ||
| * because it will re-sort previously sorted results (eg. if there is another SORT) | ||
| * or because the order will be scrambled by another command (eg. a STATS) | ||
| * <p> | ||
| * This rule finds and prunes redundant SORTs, attempting to make the plan executable. | ||
| */ | ||
| public class PruneRedundantOrderBy extends OptimizerRules.OptimizerRule<LogicalPlan> { | ||
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| @Override | ||
| protected LogicalPlan rule(LogicalPlan plan) { | ||
| if (plan instanceof OrderBy || plan instanceof TopN || plan instanceof Aggregate) { | ||
| IdentityHashMap<OrderBy, Void> redundant = findRedundantSort(((UnaryPlan) plan).child()); | ||
| if (redundant.isEmpty()) { | ||
| return plan; | ||
| } | ||
| return plan.transformDown(p -> { | ||
| if (redundant.containsKey(p)) { | ||
| return ((OrderBy) p).child(); | ||
| } | ||
| return p; | ||
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| }); | ||
| } else { | ||
| return plan; | ||
| } | ||
| } | ||
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| /** | ||
| * breadth-first recursion to find redundant SORTs in the children tree. | ||
| */ | ||
| private IdentityHashMap<OrderBy, Void> findRedundantSort(LogicalPlan plan) { | ||
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| IdentityHashMap<OrderBy, Void> result = new IdentityHashMap<>(); | ||
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| Deque<LogicalPlan> toCheck = new ArrayDeque<>(); | ||
| toCheck.push(plan); | ||
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| while (true) { | ||
| if (toCheck.isEmpty()) { | ||
| return result; | ||
| } | ||
| LogicalPlan p = toCheck.pop(); | ||
| if (p instanceof OrderBy ob) { | ||
| result.put(ob, null); | ||
| toCheck.push(ob.child()); | ||
| } else if (p instanceof SortAware sa && sa.dependsOnInputOrder() == false) { | ||
| for (LogicalPlan child : p.children()) { | ||
| toCheck.push(child); | ||
| } | ||
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| } | ||
| } | ||
| } | ||
| } | ||
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++ to the deletion, the rule was unfortunately incorrect.