Preventing System.InvalidOperationException in Azure Functions
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?
Answers
Explanations
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A. B. C. D.C.
With the Premium plan the max outbound connections per instance is unbounded compared to the 600 active (1200 total) in a Consumption plan.
Note: The number of available connections is limited partly because a function app runs in a sandbox environment.
One of the restrictions that the sandbox imposes on your code is a limit on the number of outbound connections, which is currently 600 active (1,200 total) connections per instance.
When you reach this limit, the functions runtime writes the following message to the logs: Host thresholds exceeded: Connections.
https://docs.microsoft.com/en-us/azure/azure-functions/manage-connections https://docs.microsoft.com/en-us/azure/azure-functions/functions-scale#service-limitsThe System.InvalidOperationException with the 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." occurs when the Azure function is unable to obtain a database connection from the connection pool due to all the connections being in use and the maximum pool size being reached. This issue can be resolved by increasing the connection pool size or by optimizing the way the function connects to the database.
Option A, decreasing the value of the batchSize option in the host.json file, will not prevent the InvalidOperationException from occurring. This option is used to control the batch size of messages processed by the function, and it is not related to database connections.
Option B, converting the trigger to Azure Event Hub, will not prevent the InvalidOperationException from occurring. Event Hub is a different type of trigger that is not related to the database connection pool.
Option C, converting the Azure Function to the Premium plan, may help prevent the InvalidOperationException from occurring. The Premium plan provides access to higher scale and performance capabilities that can help manage the connection pool more efficiently. However, this solution may not be cost-effective for all scenarios.
Option D, changing the value of the type option to queueScaling in the function.json file, will not prevent the InvalidOperationException from occurring. This option is used to configure scaling for the function based on the number of messages in the queue, and it is not related to database connections.
In conclusion, the best solution to prevent the System.InvalidOperationException with the 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." from occurring is to optimize the way the function connects to the database by increasing the connection pool size or by using efficient connection management techniques. If the performance requirements cannot be met with these optimizations, then upgrading to the Premium plan may be necessary.
