> For the complete documentation index, see [llms.txt](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/messaging-troubleshooting/a-missing-event-among-billions-how-we-found-it-on-an-event-mesh/day-13-13-use-case-8-non-completed-receipt.md).
# Day 13/13 Use Case 8: Non-Completed Receipt
**The consumer is unable to complete the entire receiving process before a timeout occurs.**
One case we previously encountered was when the consumer was running on a VM with two CPU cores and 2GB RAM, and subscribed to a 30MB event message from the event broker. After more than an hour, the consumer could still not successfully receive the event message. Before we explain the root cause of this issue, let us first take a look at the communication logic between the client messaging library and event broker.
The client messaging library uses a single context thread to handle the event message and heartbeat transmission riding on the persistent connection.\
The client messaging library triggers the heartbeat message, and sends to the event broker every second the event broker connection is available. If the connection fails after 3 seconds and three retries (9 seconds in total), the library will terminate the connection and reconnect. Similarly, if the event broker does not receive the heartbeat and a timeout occurs, it will also disconnect the connection.
When the connection resumes, any pending unacknowledged event message will be redelivered to the client side. The client side will clean up the memory when it detects that the connection has been terminated, and will be ready to publish or subscribe to the new events.
The consumer in this case could not complete the whole subscription process due to the resource constraint, so it was caught in a loop. It would subscribe to the event, but before receiving the entire event, the connection would terminate.
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