boolean isOldestExistingOplog(long id) {
    synchronized (getOplogIdToOplog()) {
      for (long otherId : getOplogIdToOplog().keySet()) {
        if (id > otherId) {
          return false;
        }
      }

      // since the inactiveOplogs map is an LRU we need to check each one
      for (long otherId : inactiveOplogs.keySet()) {
        if (id > otherId) {
          return false;
        }
      }
    }

    return true;
  }
Return true if id is less than all the ids in the oplogIdToOplog map. Since the oldest one is
in the LINKED hash map is first we only need to compare ourselves to it.
geode-core/src/main/java/org/apache/geode/internal/cache/PersistentOplogSet.java