GCloud Pub/Sub推送订阅：能否配置限制最大未处理消息数？

Absolutely! You can restrict the maximum number of unprocessed messages for a Cloud Pub/Sub push subscription, and this directly aligns with the slow-start mechanism you referenced.

How it works with slow-start #

借助慢启动机制，Google Cloud Pub/Sub初始每次发送一条消息，每次成功投递后数量翻倍，直至达到最大并发未处理消息数。

The slow-start mechanism ramps up the number of concurrent messages sent to your endpoint starting from 1, doubling after each successful acknowledgment—this ramp-up stops once it hits the maximum unprocessed messages limit you configure.

Configuration methods #

You can set this limit through multiple approaches:

• gcloud command-line tool:
  Use the update command to adjust the maximum outstanding messages for an existing subscription:

  gcloud pubsub subscriptions update YOUR_SUBSCRIPTION_ID --max-outstanding-messages=YOUR_DESIRED_LIMIT
  

  Replace YOUR_SUBSCRIPTION_ID with your subscription's name and YOUR_DESIRED_LIMIT with the number of unprocessed messages you want to cap at (e.g., 100).

• Pub/Sub API:
  When creating or updating a subscription, set the maxOutstandingMessages field in the pushConfig section. You can also use maxOutstandingBytes if you prefer to limit based on message size instead of count.

• Google Cloud Console:
  Navigate to your Pub/Sub subscription, click Edit subscription, scroll to the Push delivery settings section, and find the Maximum outstanding messages field to input your desired limit.

Key notes #

• Once the number of unacknowledged messages reaches your configured limit, Pub/Sub will pause pushing new messages to your endpoint until you acknowledge some messages, freeing up capacity.
• This limit applies per subscription, so you can tailor it to match your endpoint's processing capabilities.

内容的提问来源于stack exchange，提问作者Kevin Abbott