@Manas Welcome to Microsoft Q&A Forum, Thank you for posting your query here!
I see that your requirement is to fetch the metrics at the Topic level.
Please note that, by default, there is no built-in metric at the Topic level. The same has been mentioned in the above comment too. Instead you can leverage the Splitting dimensions available at the metric to group and view the metrics at the Entity Level (EventHub level) as shown below:
More Info here.
The EventHub metrics which have the dimensions of Operation Result and EntityName are explained here. If you don't add dimensions, metrics are specified at the namespace level.
Entity NameName of the event hub. With the 'Incoming Requests' metric, the Entity Name dimension will see a value of '-NamespaceOnlyMetric-' in addition to all your Event Hubs. This represents request which were made at the namespace level. Examples include a request to list all Event Hubs under the namespace or requests to entities which failed authentication or authorization.Alternatively, You can enable either runtime audit logs or application metrics logs by selecting Diagnostic settings from the Monitoring section on the Event Hubs namespace page in Azure portal.
You can analyze the collected application metrics logs using the sample query shown here.
If you have any follow-up questions on this, please let us know we would be happy to help.
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