Monitoring Consumer groups processing using custom metrics

Hi Jayendran 

In regards to your question, lag is a metric that will help you understand if your consumers are able to handle the throughput your workload is currently handling.

Also if the 'total time' (message entered to eventhub until it was processed) is critical to you - then it's very important to know this number.

Throttling is something different, it mean that the capacity that currently your eventhub allocated is not able to handle the incoming requests. it worth to check the 'throughput units' you allocated to your eventhub namespace, check the Azure documentation about how many incoming messages this units can handle,  and might check the possibility to enable the 'auto-inflate throughput units' for your eventhub (also can be read in Azure documentation).

Here is a blog post discussing the throttling: How exactly does Event Hubs Throttling Work? - Microsoft Community Hub.

This document explains the quotas and limits - https://learn.microsoft.com/en-us/azure/event-hubs/event-hubs-quotas