Merge pull request #280560 from PatAltimore/patricka-message-cleanup

Add message queue cleanup troubleshooting

Author: prmerger-automator[bot]

articles/iot-edge/troubleshoot-common-errors.md

@@ -4,7 +4,7 @@ description: Resolve common issues in Azure IoT Edge solutions. Learn how to tro
 author: PatAltimore
 
 ms.author: patricka
-ms.date: 06/06/2024
+ms.date: 07/10/2024
 ms.topic: troubleshooting-general
 ms.service: iot-edge
 services: iot-edge
@@ -363,6 +363,22 @@ You don't need to disable socket activation on a distribution where socket activ
 1. Change the iotedge config to use `/var/lib/iotedge/*.sock` in both `connect` and `listen` sections
 1. If you already have modules, they have the old `/var/run/iotedge/*.sock` mounts, so `docker rm -f` them.
 
+### Message queue clean up is slow
+
+#### Symptoms
+
+The message queue isn't being cleaned up after messages are processed. The message queue grows over time and eventually causes the IoT Edge runtime to run out of memory.
+
+#### Cause
+
+The message cleanup interval is controlled by the client message TTL (time to live) and the *EdgeHub* *MessageCleanupIntervalSecs* environment variable. The default message TTL value is two hours and the default *MessageCleanupIntervalSecs* value is 30 minutes. If your application uses a TTL value that is shorter than the default and you don't adjust the *MessageCleanupIntervalSecs* value, expired messages won't be cleaned up until the next cleanup interval.
+
+#### Solution
+
+If you change the TTL value for your application that is shorter than the default, also adjust the *MessageCleanupIntervalSecs* value. The *MessageCleanupIntervalSecs* value should be significantly smaller than the smallest TTL value that the client is using. For example, if the client application defines a TTL of five minutes in the message header, set the *MessageCleanupIntervalSecs* value to one minute. These settings ensure that messages are cleaned up within six (5 + 1) minutes. 
+
+To configure the *MessageCleanupIntervalSecs* value, set the environment variable in the deployment manifest for the IoT Edge hub module. For more information about setting runtime environment variables, see [Edge Agent and Edge Hub Environment Variables](https://github.com/Azure/iotedge/blob/main/doc/EnvironmentVariables.md).
+
 ## Networking
 
 ### IoT Edge security daemon fails with an invalid hostname