AZ-204 Certification Practice Question #174

Question

You are developing an Azure function that connects to an Azure SQL Database instance. The function is triggered by an Azure Storage queue.
You receive reports of numerous System.InvalidOperationExceptions with the following message:
`Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.`
You need to prevent the exception.
What should you do?

Accepted Answer

The error "Timeout expired…all pooled connections were in use and max pool size was reached" is a SQL Server connection pool exhaustion error, not an Azure Functions scaling error. The root cause is too many simultaneous function instances each holding a SQL connection. Reducing `batchSize` in host.json limits how many queue messages are processed in parallel per function host instance, directly reducing the number of concurrent SQL connections. This is the established best practice for queue-triggered functions connecting to SQL. The 21-vote majority and 75-upvote VK7Az204 confirm A. Confidence is 83% rather than higher because the ReniRechner argument about Premium plan has some merit (Premium allows configuring max instances), but it's not the most direct solution available in the options.

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