Lesson Learned #381: The connection is broken and recovery is not possible message using API ODBC

[Jose_Manuel_Jurado]

Using a API ODBC application code explained in this URL: Lesson Learned #368: Connection Retry-Logic using ODBC API code - Microsoft Community Hub 

Let's assume the following the scenario where a connection has been established using the ODBC API, and during the execution of a query, certain events can occur after the connection has been reset due to being idle for a period of time. The driver will try to reconnect again (if possible in this driver), basically depending on the ConnectRetryCount parameter in the connection string.

1. ConnectRetryCount > 0:

If you have defined ConnectRetryCount with a value greater than 0, it means you have enabled the connection retry logic. In this case, when the connection is reset, the ODBC driver will attempt to automatically reestablish the connection. The driver will make a number of retry attempts equal to the value specified in ConnectRetryCount.

2. ConnectRetryCount < 0 or Unsupported:

If ConnectRetryCount is set to a value less than 0 or the driver does not support this parameter, it means the automatic connection retry logic is not enabled. In this scenario, when the connection is reset, the driver will not make any automatic retry attempts, and the application will need to handle the connection failure manually.

3. ConnectRetryCount > 0 but Reestablishment Not Possible:
If ConnectRetryCount is set to a value greater than 0, but the driver is unable to reestablish the connection after exhausting the specified number of retry attempts, this means that the connection could not be recovered. Despite the driver's efforts, it was not possible to establish a stable connection, and the application needs to handle this situation accordingly.

But, first, let's try to understand what is ConnectRetryCount

ConnectRetryCount and ConnectRetryInterval are parameters used in the Microsoft ODBC Driver for SQL Server to handle connection retries in case of connection failures. Let's delve into each parameter and understand their purpose in more detail:

1. ConnectRetryCount:

ConnectRetryCount specifies the number of retry attempts that the driver will make to establish a connection with the SQL Server if the initial connection attempt fails. It determines the maximum number of retries that the driver will perform.

When the driver fails to establish a connection, it will automatically retry the connection for the specified number of times, as specified by ConnectRetryCount. Each retry attempt is made after a certain delay specified by the ConnectRetryInterval parameter.

You can customize this value to meet your specific requirements.

2. ConnectRetryInterval:

ConnectRetryInterval specifies the time delay, in seconds, between each retry attempt made by the driver when establishing a connection. It determines how long the driver waits before making the next retry attempt.

The driver uses an exponential backoff algorithm to calculate the delay between retry attempts. The delay increases exponentially with each retry attempt. For example, if the ConnectRetryInterval is set to 1 second, the driver will wait 1 second before the first retry, 2 seconds before the second retry, 4 seconds before the third retry, and so on.

You can adjust this value based on your specific requirements and the expected behavior of your application.

The combination of ConnectRetryCount and ConnectRetryInterval provides a robust mechanism to handle connection failures and automatically retry the connection process. This feature is especially useful in scenarios where network connectivity is intermittent or when the SQL Server instance is temporarily unavailable.

By configuring these parameters appropriately, you can improve the reliability and resilience of your application's connection to the Azure SQL Database, ensuring that it can handle connection failures and recover automatically without manual intervention.

Note that these parameters are specific to the Microsoft ODBC Driver for SQL Server and may not be available or function the same way in other database drivers or connection libraries.

In this case, if the value of ConnectRetryCount is more than 0, Microsoft ODBC Driver will retry the connection. But, what is happening if the value is 0?

If the value of ConnectRetryCount is set to 0, it means that the Microsoft ODBC Driver for SQL Server will not perform any retry attempts in case of a connection failure. Essentially, it disables the automatic retry feature.

In this scenario, if the initial connection attempt fails, the driver will immediately return an error or exception indicating the connection failure. It will not make any additional attempts to establish the connection.

Setting ConnectRetryCount to 0 is useful when you want to handle connection failures manually in your application code. Instead of relying on the driver's automatic retry mechanism, you can implement your own logic to handle connection failures and decide whether to retry the connection or perform alternative actions based on your application's requirements.

Disabling automatic retries can be beneficial in situations where you have specific error handling and recovery mechanisms in place or when you want to have more fine-grained control over the connection process.

However, it's important to note that disabling automatic retries means that your application will not benefit from the driver's built-in retry logic. Therefore, you need to ensure that you have appropriate error handling and recovery mechanisms in place to handle connection failures effectively in your application code.

When the value of ConnectRetryCount is set to 0, and a connection failure occurs, the typical error message that you might encounter will depend on the specific programming language or framework you are using, as well as the error handling mechanism in place.

Here are some common error messages you might encounter when ConnectRetryCount is set to 0 and a connection failure occurs:

1. Connection Timeout:

You may receive an error message indicating a connection timeout. This error message indicates that the driver was unable to establish a connection to the SQL Server within the specified timeout period.

2. Connection Refused:

If the SQL Server is not available or is refusing connections, you may receive an error message indicating that the connection was refused. This error message suggests that the SQL Server instance is not accepting incoming connections.

3. Network Error:

A network error message can occur if there are network connectivity issues between your application and the SQL Server. This can happen if there is a firewall blocking the connection or if the network connection is unstable.

4. Authentication Failure:

If the connection failure is due to authentication issues, you might receive an error message indicating that the authentication failed.

This can happen if the provided credentials are incorrect or if the user does not have sufficient privileges to connect to the SQL Server.

These are just a few examples of the error messages you might encounter when ConnectRetryCount is set to 0. The specific error messages will depend on the underlying cause of the connection failure and the error handling implemented in your application. It's important to consult the documentation and error handling mechanisms specific to your programming language, framework, and the Microsoft ODBC Driver for SQL Server for more detailed and accurate error messages.

Also, depending on how the connection has been killed we could have a 10054 

Error 10054 is a common error code that can occur in network-related operations. Specifically, it is associated with the "WSAECONNRESET" error, which stands for "Connection reset by peer." This error typically indicates that the remote host (in this case, the SQL Server) has forcefully closed the connection.

In the context of the Microsoft ODBC Driver for SQL Server, encountering error 10054 could mean that the connection between your application and the SQL Server was abruptly terminated by the server. This can happen due to various reasons, such as network issues, server-side configurations, or firewall settings.

When error 10054 occurs in the context of the ODBC driver, it signifies that the connection attempt was unsuccessful due to a connection reset by the SQL Server. This can disrupt the normal flow of data and prevent the driver from establishing a stable connection.

The connection is broken and recovery is not possible

When you encounter the error message "The connection is broken and recovery is not possible" after exhausting all ConnectRetryCount attempts, it indicates that the Microsoft ODBC Driver for SQL Server has determined that the connection is irrecoverable and cannot be reestablished automatically.

This error message signifies that the driver has made multiple retry attempts, as specified by ConnectRetryCount, to establish a connection with the SQL Server. However, despite these attempts, the driver was unable to successfully establish a stable connection.

Here's a deeper analysis of what this error message implies:

1. Connection Irreparability:
The error message indicates that the driver has determined that the connection cannot be recovered or repaired automatically. It suggests that the connection failure is persistent or beyond the scope of the driver's automatic recovery mechanisms.

2. Exhausted Retry Attempts:
The error message implies that the driver has made all the retry attempts specified by ConnectRetryCount, but none of these attempts were successful in establishing a connection. It suggests that the driver has reached the maximum number of retry attempts without establishing a stable connection.

3. Manual Intervention Required:
Since the driver is unable to recover the connection automatically, the error message implies that manual intervention is necessary. It indicates that your application needs to handle this error condition and implement appropriate measures to address the connection failure.

When you receive this error message, you should consider the following steps:

a. Implement Custom Error Handling:

Your application should have custom error handling logic in place to capture this error and handle it appropriately. This may involve displaying an error message to the user, logging the error for further analysis, or initiating alternative actions depending on your application's requirements.

b. Troubleshoot Connection Issues:

The connection failure may be caused by various factors, such as network connectivity problems. It is essential to investigate and troubleshoot the underlying cause of the connection failure to resolve the issue.

c. Retry Connection or Take Alternative Actions:

After receiving this error message, you can choose to retry the connection manually using your own retry logic or implement alternative actions based on your application's requirements. These actions may include notifying the user, providing fallback options, or terminating the application gracefully.

It's important to note that the specific error message and the actions you take may depend on the programming language, framework, or error handling mechanisms you are using in your application. Therefore, consult the relevant documentation or resources specific to your application to determine the appropriate steps to handle this error condition effectively.

Enjoy!