code: public void registerExecutor(
        String appId,
        String execId,
        ExecutorShuffleInfo executorInfo) {
      AppExecId fullId = new AppExecId(appId, execId);
      logger.info("Registered executor {} with {}", fullId, executorInfo);
      if (!knownManagers.contains(executorInfo.shuffleManager)) {
        throw new UnsupportedOperationException(
          "Unsupported shuffle manager of executor: " + executorInfo);
      }
      try {
        if (db != null) {
          byte[] key = dbAppExecKey(fullId);
          byte[] value = mapper.writeValueAsString(executorInfo).getBytes(StandardCharsets.UTF_8);
          db.put(key, value);
        }
      } catch (Exception e) {
        logger.error("Error saving registered executors", e);
      }
      executors.put(fullId, executorInfo);
    }
docs: Registers a new Executor with all the configuration we need to find its shuffle files.