Grails MongoDB乐观锁定更新所有记录

Question

我有一个每日计划的grails作业，它会根据上次日期的更改来更新用户的属性。它就像这样

try {
        // Daily job for updating user orders
        DateTime yesterday = new DateTime().withZone(DateTimeZone.getDefault()).withTimeAtStartOfDay().minusDays(1)
        userService.updateStatsForAllUsers(yesterday)
    }
    catch (Exception e) {
        println e.getCause()
    }

UserService

void updateStatsForAllUsers(DateTime date) {
    List<User> customers = User.list()
    List<Order> orders = null
    customers.each { customer ->
        orders = customer.orders?.findAll{it.status.equals("DELIVERED")}?.sort{it?.dateCreated}
        if (orders?.size() > 0) {
            customer.firstOrderDate = orders?.first()?.dateCreated
            customer.lastOrderDate = orders?.last()?.dateCreated
            customer.totalOrders = orders.size()
            customer.save(flush: true)
        }
    }
}

我们有一个大约50k的用户群，这个作业总是会在用户保存时抛出一个OptimisticLockingException。我们如何处理这个问题，有没有办法使用grails mongo进行这样的批量更新。