Problem:
Sampling data from an Event Hub input of Azure Stream Analytics job failed with the following error message:
"No events found for '<input-name>'. Start time: <Day>, <Month> <Date>, <Year>, <Local Time> End time: <Day>, <Month> <Date>, <Year>, <Local Time> Last time arrival: <Day>, <Month> <Date>, <Year>, <Local Time> Diagnostics: While sampling data, no data was received from '7' partitions."
This is despite that the Event Hub metric showing messages are received and sent so that we can be sure that input data are available in the Event Hub.
Solution:
The error message indicates that there is a serialization issue in Azure Stream Analytics job.
According to the document Stream data as input into Stream Analytics, only JSON, CSV, and Avro format are supported.
Event serialization format The serialization format (JSON, CSV, or Avro) of the incoming data stream. Ensure the JSON format aligns with the specification and doesn’t include leading 0 for decimal numbers.
Therefore the next step is to verify if the message in the Event Hub has the format required by Azure Stream Analytics.
To do this, we can build a listener following this documentation:
Get started receiving messages with the Event Processor Host in .NET Standard
What we need are the Event Hubs’ connection string and name. As a side note, a connection string is the “key” to your Event Hub; anyone who has your Event Hub’s connection string can tap/listen to it, so be careful not to share this sensitive information to the parties who don’t have the authority.
When you run the program, there will be a terminal window opened that shows the messages from the Event Hub. Capture the messages and analyze the data format and structure. If it is JSON, you can validate it using a validator such as https://jsonlint.com/.
In my case, it turned out that the messages have an incorrect format that blocked Azure Stream Analytics from deserializing it. Hence the error.