NatsNoReplyException when acknowledging a message with DoubleAck = true

[stanislav-maximenco]

Observed behavior

Hi,

We are encountering an intermittent issue when acknowledging messages using the DoubleAck = true option for messages consumed via FetchAsync. The issue arises unexpectedly after successfully consuming and acknowledging many messages, sometimes it is reproduceable under certain scenarios.

Before I provide further details and diagnostics, could you please clarify whether it is recommended to use the DoubleAck feature with our specific server and client versions? Are there any known compatibility or stability concerns related to this feature?

Thank you for your assistance!

Best regards

Expected behavior

AckAsync with DoubleAck = true should not throw a NatsNoReplyException

Server and client version

Server: 2.10.28
Client: 2.5.10

Host environment

No response

Steps to reproduce

No response

[mtmk]

Thank you for the report @stanislav-maximenco. NatsNoReplyException usually happens underload or sometimes during network problems depending on your environment. A lot of the JetSream operations are performed over request-reply messaging and NatsNoReplyException means reply did not arrive on time. In .NET applications this can also happen if the thread pool was too busy somehow at the point of this error happening and could not dispatch the reply soon enough since NATS .NET client relies on the thread pool heavily because of the full async architecture it uses.

Having said all that, I would definitely suggest upgrading both server and client since there has been significant fixes in both the server and the client. Client also has a new option to increase request-reply performance NatsRequestReplyMode.Direct you can also try that.

nats.net/src/NATS.Client.Core/NatsOpts.cs

Line 176 in a20cfed

public NatsRequestReplyMode RequestReplyMode { get; init; } = NatsRequestReplyMode.SharedInbox;