UNDF: UNDF-2026-000000543

starrocks-0001: MaterializedViewRewriter.getTableToRelationid — List.contains in column-ref loop → O(N×T)

Classification

Severity: HIGH
CWE: CWE-407 (Algorithmic Complexity — Inefficient Algorithmic Complexity)
Component: fe/fe-core/src/main/java/com/starrocks/sql/optimizer/rule/transformation/materialization/MaterializedViewRewriter.java
Method: getTableToRelationid()

Defect

getTableToRelationid() iterates over every column-ref-to-table mapping in the ColumnRefFactory (up to N entries for wide schemas) and calls tableList.contains(entry.getValue()) where tableList is the List<Table> parameter.

private Map<Table, Set<Integer>> getTableToRelationid(
        OptExpression optExpression, ColumnRefFactory refFactory, List<Table> tableList) {
    ...
    for (Map.Entry<ColumnRefOperator, Table> entry : refFactory.getColumnRefToTable().entrySet()) {
        if (!tableList.contains(entry.getValue())) {   // <-- O(T) List.contains
            continue;
        }
        ...
    }
}

List.contains() is O(T) where T is the number of tables. The loop runs N times (one per column ref). Total: O(N × T).

The method is called twice per MV rewrite candidate — once for the query expression and once for the MV expression (lines 2645 and 2656). MV rewrite is attempted for every applicable MV on every query, so in workloads with many columns and multiple MVs this compounds quickly.

A production StarRocks deployment with 500 column refs and 20 candidate tables performs 10 000 list-scans per call, repeated for every MV candidate at query-compilation time.

Root Cause

The caller (rewrite()/generateRelationIdMap()) has List<Table> queryTables / mvTables which are passed directly to getTableToRelationid. The lists are never converted to sets before the call.

Fix

Convert tableList to a HashSet once before the loop. Each .contains() becomes O(1).

// Before:
if (!tableList.contains(entry.getValue())) {   // O(T) per iteration

// After:
Set<Table> tableSet = new HashSet<>(tableList); // O(T) once, before loop
...
if (!tableSet.contains(entry.getValue())) {     // O(1) per iteration

Alternatively, change the parameter type from List<Table> to Set<Table> and update callers to pass new HashSet<>(queryTables) / new HashSet<>(mvTables).

Complexity

Before	After
O(N × T) per call	O(N + T) per call

With N=500 column refs, T=20 tables: Before = 10 000 comparisons. After = 520. ~19× reduction. Called twice per MV candidate; with 10 MVs = 200 000 → 10 400 comparisons total.

Patch

--- a/fe/fe-core/src/main/java/com/starrocks/sql/optimizer/rule/transformation/materialization/MaterializedViewRewriter.java
+++ b/fe/fe-core/src/main/java/com/starrocks/sql/optimizer/rule/transformation/materialization/MaterializedViewRewriter.java
@@ -2777,9 +2777,11 @@ public class MaterializedViewRewriter {
     private Map<Table, Set<Integer>> getTableToRelationid(
             OptExpression optExpression, ColumnRefFactory refFactory, List<Table> tableList) {
         Map<Table, Set<Integer>> tableToRelationId = Maps.newHashMap();
         Set<ColumnRefOperator> validColumnRefs = MvUtils.collectScanColumn(optExpression);
+        // Convert to HashSet once — avoids O(T) List.contains per column-ref iteration
+        Set<Table> tableSet = new HashSet<>(tableList);
         for (Map.Entry<ColumnRefOperator, Table> entry : refFactory.getColumnRefToTable().entrySet()) {
-            if (!tableList.contains(entry.getValue())) {
+            if (!tableSet.contains(entry.getValue())) {
                 continue;
             }

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