# 조립된 경로에서 갱신과 원장 기록 사이에 있는 것
    // Still refreshed after execute, but the refresh is no longer what protects the run: the
    // heartbeat inside the context is. This one only proves the lease survived to the end, before
    // anything is written to the ledger under it.
    lock.refresh(template.maxTime());
    if (!migration.postcondition().isSatisfied(context, result)) {
      throw MongoOperationRejectedException.of(
          "migration.postcondition",
          "migration "
              + migration.id()
  ...
    result.resumePoint().ifPresent(checkpoint -> ledger.saveCheckpoint(checkpoint, lock.fence()));
    if (result.status() == MongoMigrationResult.Status.COMPLETED && !context.dryRun()) {
      ledger.recordApplied(
          migration.id(), migration.checksum(), context.operator(), clock.instant(), lock.fence());
    }

#   완료를 만드는 팩토리는 체크포인트를 남기지 않는다
  /** The migration finished. */
  public static MongoMigrationResult completed(long processedCount) {
    return new MongoMigrationResult(Status.COMPLETED, processedCount, null, "");
  }

  /** The migration made progress and stored a checkpoint to resume from. */
  public static MongoMigrationResult incomplete(
      long processedCount, MongoMigrationCheckpoint checkpoint) {
    return new MongoMigrationResult(
        Status.INCOMPLETE, processedCount, Objects.requireNonNull(checkpoint, "checkpoint"), "");
  }

#   그 갱신이 던지는 것
    if (stillOwned != 1) {
      held = false;
      throw new IllegalStateException(
          "the migration lease was lost before it could be refreshed; another runner may have "
              + "taken it after this one appeared to stall");
    }
#   같은 인터페이스의 다른 잠금 구현이 같은 상황에 던지는 것
  public void refresh(Duration extension) {
    Objects.requireNonNull(extension, "extension");
    if (!held.get()) {
      throw MongoOperationRejectedException.of(
          "migration.lock", "the migration lease has been released and cannot be extended");
    }
    extend.accept(extension);

# 다른 원장 구현은 펜스 인자를 쓰지 않는다
      long fence) {
    recorded.put(
        Objects.requireNonNull(migrationId, "migrationId"),
        new AppliedMigration(migrationId, checksum, operator, appliedAt));
  }

# recordApplied 를 부르는 시험 전수
MongoMigrationRunnerTest.java:23:    ledger.recordApplied(
MongoMigrationRunnerTest.java:40:    ledger.recordApplied(
MongoMigrationLaneTest.java:130:    ledger.recordApplied(
MongoMigrationLaneTest.java:227:    ledger.recordApplied(id, new MongoMigrationChecksum("abc"), "operator", FIXED.instant(), 1L);
MongoMigrationLaneTest.java:231:                ledger.recordApplied(
#   그중 실서버에서 두 번 부르는 시험이 단언하는 것
            () ->
                ledger.recordApplied(
                    id, new MongoMigrationChecksum("abc"), "operator", FIXED.instant(), 1L))
        .as("the unique index, not the read-then-write check, is what makes this impossible")
        .isInstanceOf(RuntimeException.class);

# 고유 색인을 만드는 메서드를 부르는 곳 전수
test/java/dev/caskeleton/adapter/outbound/mongo/migration/MongoMigrationLaneTest.java
main/java/dev/caskeleton/adapter/outbound/mongo/migration/MongoCollectionMigrationLedger.java