private OperationQuota getQuota(String userName) {
    QuotaLimiter userLimiter = throttleQuotaLimit.getUserLimiter(userName);
    if (userLimiter != null) {
      return new DefaultOperationQuota(userLimiter);
    }
    return NoopOperationQuota.get();
  }
Returns the quota for an operation.

@param userName login user
@return the {@link OperationQuota}
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/rescon/quotas/DataNodeThrottleQuotaManager.java