MySQL 慢查询排查：时间到底花在哪里

import java.util.*;

public class Main {
  record Span(String kind, long start, long end) {}
  record Report(Map<String, Long> byKind, long covered, long unknown) {}
  static long union(List<Span> spans) {
    if (spans.isEmpty()) return 0;
    List<Span> sorted = new ArrayList<>(spans);
    sorted.sort(Comparator.comparingLong(Span::start).thenComparingLong(Span::end));
    long left = sorted.get(0).start(), right = sorted.get(0).end(), total = 0;
    for (int i = 1; i < sorted.size(); i++) {
      Span s = sorted.get(i);
      if (s.start() <= right) right = Math.max(right, s.end()); // 重叠或相邻可合并
      else {
        total += right - left; // 仅结算互不重叠的完整区间
        left = s.start(); right = s.end();
      }
    }
    return total + right - left;
  }
  static Report analyze(long duration, List<Span> spans) {
    if (duration < 0) throw new IllegalArgumentException("duration");
    Map<String, List<Span>> groups = new TreeMap<>();
    for (Span s : spans) {
      if (s.kind() == null || s.start() < 0 || s.end() < s.start() || s.end() > duration)
        throw new IllegalArgumentException("span"); // 拒绝错误时钟与越界输入
      groups.computeIfAbsent(s.kind(), k -> new ArrayList<>()).add(s);
    }
    Map<String, Long> totals = new TreeMap<>();
    groups.forEach((kind, group) -> totals.put(kind, union(group)));
    long covered = union(spans); // 类别之间可能重叠，必须单独算全量并集
    return new Report(Map.copyOf(totals), covered, duration - covered);
  }
  static void check(boolean ok) { if (!ok) throw new AssertionError(); }
  static void bad(Runnable action) {
    try { action.run(); } catch (IllegalArgumentException expected) { return; }
    throw new AssertionError("expected invalid input");
  }
  public static void main(String[] args) {
    Report r = analyze(100, List.of(new Span("SQL",20,60),
        new Span("SQL",40,80), new Span("POOL",0,20)));
    check(r.byKind().get("SQL") == 60 && r.covered() == 80 && r.unknown() == 20);
    check(analyze(10, List.of()).unknown() == 10);
    r = analyze(10, List.of(new Span("A",0,10), new Span("B",2,8)));
    check(r.covered() == 10 && r.byKind().get("B") == 6);
    check(analyze(10, List.of(new Span("A",5,5))).covered() == 0);
    check(analyze(10, List.of(new Span("A",5,10), new Span("A",0,5))).covered() == 10);
    bad(() -> analyze(10, List.of(new Span("A",0,11))));
    bad(() -> analyze(10, List.of(new Span("A",8,3))));
    System.out.println("7 interval attribution checks passed");
  }
}