java-topology/defects/clickhouse/unit/ClickHouseReplaceTransformerAlgorithm.java

package unit;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Unit test for CWE-407 defect in ClickHouse ReplaceColumnTransformerNode::findReplacementExpression.
 *
 * Defect: replacements_names is a std::vector<std::string>. findReplacementExpression() does
 * std::find (O(n)) over it. It is called inside a double loop:
 *   for each column (C) → for each transformer (T) → findReplacementExpression() → O(R)
 * Total: O(C * T * R). For wide-table queries with compound REPLACE lists this is measurable.
 *
 * Fix: add std::unordered_map<std::string, size_t> replacements_index alongside replacements_names.
 * findReplacementExpression() becomes O(1) via map lookup.
 *
 * This test models slow (list scan) vs fast (map lookup) and asserts
 * slow ops > fast ops * 10x at N=200 replacements, 500 column lookups.
 */
public class ClickHouseReplaceTransformerAlgorithm {

    // -----------------------------------------------------------------------
    // slow(): models std::find scan over Names (vector<string>).
    // Returns total comparison ops.
    // -----------------------------------------------------------------------
    static Result slow(int numReplacements, int numLookups) {
        List<String> names = new ArrayList<>();
        for (int i = 0; i < numReplacements; i++) {
            names.add("col_" + i);
        }

        long ops = 0;
        // Simulate findReplacementExpression called numLookups times,
        // always looking for the last element (worst case).
        String target = "col_" + (numReplacements - 1);
        for (int q = 0; q < numLookups; q++) {
            for (int j = 0; j < names.size(); j++) {
                ops++;
                if (names.get(j).equals(target)) {
                    break;
                }
            }
        }
        return new Result(ops);
    }

    // -----------------------------------------------------------------------
    // fast(): models unordered_map<string, size_t> lookup → O(1).
    // Returns total lookup ops (1 per call).
    // -----------------------------------------------------------------------
    static Result fast(int numReplacements, int numLookups) {
        Map<String, Integer> index = new HashMap<>();
        for (int i = 0; i < numReplacements; i++) {
            index.put("col_" + i, i);
        }

        long ops = 0;
        String target = "col_" + (numReplacements - 1);
        for (int q = 0; q < numLookups; q++) {
            ops++; // O(1) hash lookup
            @SuppressWarnings("unused")
            Integer idx = index.get(target);
        }
        return new Result(ops);
    }

    // -----------------------------------------------------------------------
    static class Result {
        final long ops;
        Result(long ops) { this.ops = ops; }
    }

    // -----------------------------------------------------------------------
    public static void main(String[] args) {
        int N = 200;
        int lookups = 500;
        int NX = 10;

        Result s = slow(N, lookups);
        Result f = fast(N, lookups);

        System.out.printf("slow ops=%d  fast ops=%d  ratio=%.1fx%n",
                s.ops, f.ops, (double) s.ops / f.ops);

        if (s.ops <= f.ops * NX) {
            System.out.printf("FAIL: expected slow(%d) > fast(%d) * %d%n", s.ops, f.ops, NX);
            System.exit(1);
        }

        System.out.printf("1/1 PASS  (slow=%d >> fast=%d, N=%d lookups=%d)%n",
                s.ops, f.ops, N, lookups);
    }
}