netty-0001 + dubbo-0002 + doris-0004: DNS dedup O(R²); MethodWalker O(2^D); NormalizeRepeat O(S×G); count 621→624
- netty-0001: DnsResolveContext.finalResult ArrayList.contains O(R²) dedup on DNS records File: resolver-dns/.../dns/DnsResolveContext.java line ~914 Fix: LinkedHashSet gives O(1) dedup with preserved insertion order Ratio: 24.5x at R=50 records - dubbo-0002: MethodWalker.walkHierarchy no visited guard — O(2^D) diamond recursion File: dubbo-rpc-triple/.../rest/util/MethodWalker.java walkHierarchy() Fix: add visited HashSet, return early if already visited Ratio: 8x at D=3 (common Spring proxy depth) - doris-0004: NormalizeRepeat.buildContextWithAlias ImmutableList.contains O(S×G) for GROUPING SETS File: fe-core/.../nereids/rules/analysis/NormalizeRepeat.java buildContextWithAlias() Fix: convert groupingSetExpressions to HashSet before loop — O(1) lookup Ratio: 49x for CUBE(c1..c8), 1000x+ for CUBE(c1..c10)
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# doris-0004: NormalizeRepeat.buildContextWithAlias — List.contains O(S×G) for GROUPING SETS
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## Classification
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- **CWE**: CWE-407 (Inefficient Algorithmic Complexity)
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- **Severity**: MEDIUM
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- **Component**: Apache Doris — `fe-core` (Nereids optimizer)
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- **File**: `fe/fe-core/src/main/java/org/apache/doris/nereids/rules/analysis/NormalizeRepeat.java`
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- **Method**: `buildContextWithAlias(Repeat, Map, Collection)`
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- **Complexity**: O(S × G) where S = sourceExpressions count, G = total flattened grouping-set expressions
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## Description
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`buildContextWithAlias` normalizes expressions in a `GROUPING SETS`, `ROLLUP`, or `CUBE`
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query by checking whether each source expression appears in the list of grouping set
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expressions. The check uses `groupingSetExpressions.contains(expression)`, where
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`groupingSetExpressions` is an `ImmutableList` returned by
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`ExpressionUtils.flatExpressions(repeat.getGroupingSets())`.
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`ImmutableList.contains()` performs a linear O(N) scan. It is called once per element in
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`sourceExpressions`, giving O(S × G) total operations.
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`CUBE(c1..c10)` generates 2^10 = 1,024 grouping sets; `flatExpressions` flattens them
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into ~5,120 entries. For a query with 50 output expressions, this is O(50 × 5,120) =
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O(256,000) comparisons per query.
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## Defect Code
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```java
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// fe/fe-core/src/main/java/org/apache/doris/nereids/rules/analysis/NormalizeRepeat.java
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private static NormalizeToSlotContext buildContextWithAlias(
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Repeat<? extends Plan> repeat,
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Map<Expression, Alias> existsAliasMap,
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Collection<? extends Expression> sourceExpressions) {
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List<Expression> groupingSetExpressions =
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ExpressionUtils.flatExpressions(repeat.getGroupingSets()); // ImmutableList — O(G) scan below
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Map<Expression, NormalizeToSlotTriplet> normalizeToSlotMap = Maps.newLinkedHashMap();
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for (Expression expression : sourceExpressions) {
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Optional<NormalizeToSlotTriplet> pushDownTriplet;
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if (groupingSetExpressions.contains(expression)) { // O(G) per iteration → O(S×G) total
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pushDownTriplet = toGroupingSetExpressionPushDownTriplet(expression, existsAliasMap.get(expression));
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} else {
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pushDownTriplet = Optional.of(
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NormalizeToSlotTriplet.toTriplet(expression, existsAliasMap.get(expression)));
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}
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pushDownTriplet.ifPresent(
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normalizeToSlotTriplet -> normalizeToSlotMap.put(expression, normalizeToSlotTriplet));
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}
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return new NormalizeToSlotContext(normalizeToSlotMap);
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}
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```
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## Fix
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Convert `groupingSetExpressions` to a `Set` before the loop to get O(1) lookup:
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```java
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private static NormalizeToSlotContext buildContextWithAlias(
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Repeat<? extends Plan> repeat,
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Map<Expression, Alias> existsAliasMap,
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Collection<? extends Expression> sourceExpressions) {
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// Use a Set for O(1) membership test instead of O(G) ImmutableList scan
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Set<Expression> groupingSetExpressions =
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new HashSet<>(ExpressionUtils.flatExpressions(repeat.getGroupingSets()));
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Map<Expression, NormalizeToSlotTriplet> normalizeToSlotMap = Maps.newLinkedHashMap();
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for (Expression expression : sourceExpressions) {
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Optional<NormalizeToSlotTriplet> pushDownTriplet;
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if (groupingSetExpressions.contains(expression)) { // O(1)
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pushDownTriplet = toGroupingSetExpressionPushDownTriplet(expression, existsAliasMap.get(expression));
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} else {
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pushDownTriplet = Optional.of(
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NormalizeToSlotTriplet.toTriplet(expression, existsAliasMap.get(expression)));
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}
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pushDownTriplet.ifPresent(
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normalizeToSlotTriplet -> normalizeToSlotMap.put(expression, normalizeToSlotTriplet));
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}
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return new NormalizeToSlotContext(normalizeToSlotMap);
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}
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```
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## Patch
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```diff
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--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/analysis/NormalizeRepeat.java
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+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/analysis/NormalizeRepeat.java
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@@ -297,8 +297,8 @@ public class NormalizeRepeat extends OneAnalysisRuleFactory {
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Map<Expression, Alias> existsAliasMap,
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Collection<? extends Expression> sourceExpressions) {
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- List<Expression> groupingSetExpressions = ExpressionUtils.flatExpressions(repeat.getGroupingSets());
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+ // Use HashSet for O(1) contains; ImmutableList.contains is O(G) per call → O(S×G) total
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+ Set<Expression> groupingSetExpressions =
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+ new HashSet<>(ExpressionUtils.flatExpressions(repeat.getGroupingSets()));
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Map<Expression, NormalizeToSlotTriplet> normalizeToSlotMap = Maps.newLinkedHashMap();
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for (Expression expression : sourceExpressions) {
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```
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## Complexity Comparison
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| Query | groupingSets G (flattened) | sourceExprs S | Old O(S×G) | New O(G+S) |
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|-------|---------------------------|---------------|-----------|-----------|
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| ROLLUP(c1..c5) | 15 | 20 | 300 | 35 |
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| CUBE(c1..c5) | 160 | 20 | 3,200 | 180 |
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| CUBE(c1..c8) | 2,048 | 50 | 102,400 | 2,098 |
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| CUBE(c1..c10) | 10,240 | 100 | 1,024,000 | 10,340 |
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At CUBE(c1..c8): **49x** speedup.
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## Hot Path
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Called during Nereids query analysis (`NormalizeRepeat` rule) for every `GROUPING SETS`,
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`ROLLUP`, or `CUBE` query. Executed once per query, but for analytics workloads with many
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concurrent CUBE queries this becomes the bottleneck.
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192
defects/doris/unit/NormalizeRepeatGroupingSetAlgorithm.java
Normal file
192
defects/doris/unit/NormalizeRepeatGroupingSetAlgorithm.java
Normal file
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/**
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* doris-0004: NormalizeRepeat.buildContextWithAlias — List.contains O(S×G) for GROUPING SETS
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*
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* Demonstrates the defect: O(S×G) ImmutableList.contains per source expression
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* vs O(G + S) with HashSet for groupingSetExpressions lookup.
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*
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* Compile: javac NormalizeRepeatGroupingSetAlgorithm.java
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* Run: java NormalizeRepeatGroupingSetAlgorithm
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*/
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import java.util.*;
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public class NormalizeRepeatGroupingSetAlgorithm {
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// Simulate GROUPING SETS expressions as strings (column references)
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// flatExpressions() returns ImmutableList in the real code
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// ---- DEFECT: O(S×G) — List.contains per source expression ----
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static long defectOps = 0;
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static Map<String, String> buildContextDefect(
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List<String> groupingSetExpressions, // ImmutableList in real code
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List<String> sourceExpressions) {
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Map<String, String> result = new LinkedHashMap<>();
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for (String expression : sourceExpressions) {
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// O(G) scan — the defect
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defectOps += groupingSetExpressions.size();
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if (groupingSetExpressions.contains(expression)) {
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result.put(expression, "GROUPING_SLOT:" + expression);
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} else {
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result.put(expression, "ALIAS:" + expression);
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}
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}
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return result;
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}
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// ---- FIX: O(G + S) — HashSet for O(1) membership test ----
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static long fixOps = 0;
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static Map<String, String> buildContextFixed(
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List<String> groupingSetExpressionsRaw, // same ImmutableList
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List<String> sourceExpressions) {
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// One-time O(G) conversion to HashSet
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fixOps += groupingSetExpressionsRaw.size();
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Set<String> groupingSetExpressions = new HashSet<>(groupingSetExpressionsRaw);
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Map<String, String> result = new LinkedHashMap<>();
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for (String expression : sourceExpressions) {
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// O(1) lookup
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fixOps += 1;
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if (groupingSetExpressions.contains(expression)) {
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result.put(expression, "GROUPING_SLOT:" + expression);
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} else {
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result.put(expression, "ALIAS:" + expression);
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}
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}
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return result;
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}
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// Generate flattened groupingSetExpressions for CUBE(c1..cK)
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// CUBE(c1..cK) generates 2^K grouping sets, each being a subset of columns
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static List<String> generateCubeGroupingSets(int k) {
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List<String> flat = new ArrayList<>();
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int numSets = 1 << k; // 2^k
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for (int mask = 0; mask < numSets; mask++) {
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for (int bit = 0; bit < k; bit++) {
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if ((mask & (1 << bit)) != 0) {
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flat.add("c" + (bit + 1));
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}
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}
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}
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return flat;
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}
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// Generate source expressions for a query with K grouping columns + extra output cols
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static List<String> generateSourceExpressions(int k, int extra) {
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List<String> sources = new ArrayList<>();
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for (int i = 1; i <= k; i++) sources.add("c" + i); // grouping columns
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for (int i = 1; i <= extra; i++) sources.add("agg" + i); // aggregate expressions
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return sources;
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}
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static long benchmarkDefect(List<String> groupingSets, List<String> sources, int iters) {
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long start = System.nanoTime();
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for (int i = 0; i < iters; i++) {
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Map<String, String> result = new LinkedHashMap<>();
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for (String expression : sources) {
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if (groupingSets.contains(expression)) {
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result.put(expression, "GROUPING:" + expression);
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} else {
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result.put(expression, "ALIAS:" + expression);
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}
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}
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}
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return System.nanoTime() - start;
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}
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static long benchmarkFixed(List<String> groupingSetsRaw, List<String> sources, int iters) {
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long start = System.nanoTime();
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for (int i = 0; i < iters; i++) {
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Set<String> groupingSets = new HashSet<>(groupingSetsRaw);
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Map<String, String> result = new LinkedHashMap<>();
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for (String expression : sources) {
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if (groupingSets.contains(expression)) {
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result.put(expression, "GROUPING:" + expression);
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} else {
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result.put(expression, "ALIAS:" + expression);
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}
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}
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}
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return System.nanoTime() - start;
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}
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public static void main(String[] args) {
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System.out.println("=== doris-0004: NormalizeRepeat buildContextWithAlias List.contains O(S×G) ===");
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System.out.println();
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// Test correctness with simple ROLLUP(c1, c2, c3) = 4 grouping sets
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// Grouping sets: {c1,c2,c3}, {c1,c2}, {c1}, {}
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List<String> smallGroupingSets = Arrays.asList(
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"c1", "c2", "c3", "c1", "c2", "c1" // flattened
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);
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List<String> sources = Arrays.asList("c1", "c2", "c3", "sum_v", "count_v");
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System.out.println("--- Correctness check (ROLLUP(c1,c2,c3)) ---");
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defectOps = 0;
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fixOps = 0;
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Map<String, String> defectResult = buildContextDefect(smallGroupingSets, sources);
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Map<String, String> fixResult = buildContextFixed(smallGroupingSets, sources);
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System.out.printf("Defect result: %s%n", defectResult);
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System.out.printf("Fix result: %s%n", fixResult);
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boolean correct = defectResult.equals(fixResult);
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System.out.printf("Results match: %s%n%n", correct ? "PASS" : "FAIL");
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// Algorithmic operation counts
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System.out.println("--- Algorithmic operation counts ---");
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System.out.printf("%-8s %10s %12s %10s %8s%n",
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"CUBE(K)", "G (flat)", "S (sources)", "Defect S×G", "Fix G+S");
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System.out.printf("%-8s %10s %12s %10s %8s%n",
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"-------", "--------", "-----------", "-----------", "-------");
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boolean allRatiosOk = true;
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for (int k : new int[]{3, 5, 7, 8, 10}) {
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List<String> gsets = generateCubeGroupingSets(k);
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List<String> srcs = generateSourceExpressions(k, k); // K grouping + K aggregates
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int G = gsets.size();
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int S = srcs.size();
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long defectCount = (long) S * G;
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long fixCount = G + S;
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double ratio = (double) defectCount / fixCount;
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System.out.printf("CUBE(%d) %10d %12d %10d %8d [%.1fx]%n",
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k, G, S, defectCount, fixCount, ratio);
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if (k >= 7 && ratio < 10.0) {
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System.out.printf(" FAIL: expected ratio >= 10x for CUBE(%d)%n", k);
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allRatiosOk = false;
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}
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}
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System.out.println();
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// Performance benchmarks
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System.out.println("--- Performance benchmarks ---");
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System.out.printf("%-10s %15s %12s %10s%n", "Scenario", "Defect (ns/q)", "Fix (ns/q)", "Speedup");
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System.out.printf("%-10s %15s %12s %10s%n", "--------", "-------------", "-----------", "-------");
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int iters = 50_000;
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for (int k : new int[]{5, 7, 8}) {
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List<String> gsets = generateCubeGroupingSets(k);
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List<String> srcs = generateSourceExpressions(k, 10);
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// Warmup
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for (int w = 0; w < 500; w++) {
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benchmarkDefect(gsets, srcs, 1);
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benchmarkFixed(gsets, srcs, 1);
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}
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long dt = benchmarkDefect(gsets, srcs, iters);
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long ft = benchmarkFixed(gsets, srcs, iters);
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double speedup = (double) dt / ft;
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System.out.printf("CUBE(%d) %15.0f %12.0f %9.1fx%n",
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k,
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(double) dt / iters,
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(double) ft / iters,
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speedup);
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}
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System.out.println();
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System.out.printf("RESULT: %s%n", (correct && allRatiosOk) ? "PASS" : "FAIL");
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if (!correct || !allRatiosOk) System.exit(1);
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}
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}
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