在delivery_attempt超过max_delivery_attempts之后，将PubSub转发到死信主题的消息

Question

我的订户看起来像这样：

from google.cloud import pubsub_v1
from google.cloud.pubsub_v1.types import DeadLetterPolicy

dead_letter_policy = DeadLetterPolicy(
    dead_letter_topic='dead_letter_topic',
    max_delivery_attempts=5,
)

topic_path = subscriber.topic_path(PROJECT, TOPIC)
subscriber.create_subscription(sub_path, topic_path, dead_letter_policy=dead_letter_policy)

subscriber = pubsub_v1.SubscriberClient()
subscription_path  = subscriber.subscription_path(PROJECT, SUBSCRIPTION)

def callback(message):
    print("Received message: {}".format(message))
    print('Attempted:', message.delivery_attempt, 'times')
    data = message.data.decode('utf-8')
    data_d = json.loads(data)
    if data_d["name"] == "some_file.json":
        message.nack()
    else:
        message.ack()

收到的消息看起来像这样：

Received message: Message {
  data: b'{\n  "kind": "storage#object",\n  "id": "...'
  attributes: {
    "bucketId": "sample_bucket",
    ...
  }
}
Attempted: 12 times

显然，它尝试了5次以上，为什么我仍然可以从PubSub主题中提取此消息？这是订阅信息：

ackDeadlineSeconds: 10
deadLetterPolicy:
  deadLetterTopic: projects/someproject/topics/dead_letter
  maxDeliveryAttempts: 5
expirationPolicy:
  ttl: 2678400s
messageRetentionDuration: 604800s
name: projects/someproject/subscriptions/new_sub
pushConfig: {}
topic: projects/someproject/topics/pubsub_sample

Answer 1