Should non-idempotent operations be called with a retry policy?

So I guess the question is, is there any other reason to not call it with a retry policy that I haven't thought about?

To be able to use retry the following criteria group should be met:

• The potentially introduced observable impact is acceptable
• The operation can be redone without any irreversible side effect
• The introduced complexity is negligible compared to the promised reliability

In other words

• If the delay of potential retries is not tolerable for your consumers then don't use retry
• If the retry might produce some unwanted side-effect which is irreversible then don't use retry
• If the retry logic (+ the usage of other policies, like timeout) makes your application much harder to monitor and maintain then don't use retry

To reflect to your example

It might happen that the SQL server commits your transaction but unable to respond back to your application. In that case if you blindly retry it then you might end up having duplicates or even worse.

Most of the time I suggest to perform retry against databases whenever we know that the database acknowledges the transient error, like deadlock, resource limit has been reached, etc.

In case of Entity Framework Core there is a built-in retry support, here you can find the status codes against which the retry can be performed.

// SQL Error Code: 49920
// Cannot process request. Too many operations in progress for subscription "%ld".
// The service is busy processing multiple requests for this subscription.
// Requests are currently blocked for resource optimization. Query sys.dm_operation_status for operation status.
// Wait until pending requests are complete or delete one of your pending requests and retry your request later.
case 49920:
// SQL Error Code: 49919
// Cannot process create or update request. Too many create or update operations in progress for subscription "%ld".
// The service is busy processing multiple create or update requests for your subscription or server.
// Requests are currently blocked for resource optimization. Query sys.dm_operation_status for pending operations.
// Wait till pending create or update requests are complete or delete one of your pending requests and
// retry your request later.
case 49919:
// SQL Error Code: 49918
// Cannot process request. Not enough resources to process request.
// The service is currently busy.Please retry the request later.
case 49918:
// SQL Error Code: 41839
// Transaction exceeded the maximum number of commit dependencies.
case 41839:
// SQL Error Code: 41325
// The current transaction failed to commit due to a serializable validation failure.
case 41325:
// SQL Error Code: 41305
// The current transaction failed to commit due to a repeatable read validation failure.
case 41305:
// SQL Error Code: 41302
// The current transaction attempted to update a record that has been updated since the transaction started.
case 41302:
// SQL Error Code: 41301
// Dependency failure: a dependency was taken on another transaction that later failed to commit.
case 41301:
// SQL Error Code: 40613
// Database XXXX on server YYYY is not currently available. Please retry the connection later.
// If the problem persists, contact customer support, and provide them the session tracing ID of ZZZZZ.
case 40613:
// SQL Error Code: 40501
// The service is currently busy. Retry the request after 10 seconds. Code: (reason code to be decoded).
case 40501:
// SQL Error Code: 40197
// The service has encountered an error processing your request. Please try again.
case 40197:
// SQL Error Code: 10936
// Resource ID : %d. The request limit for the elastic pool is %d and has been reached.
// See 'http://go.microsoft.com/fwlink/?LinkId=267637' for assistance.
case 10936:
// SQL Error Code: 10929
// Resource ID: %d. The %s minimum guarantee is %d, maximum limit is %d and the current usage for the database is %d.
// However, the server is currently too busy to support requests greater than %d for this database.
// For more information, see http://go.microsoft.com/fwlink/?LinkId=267637. Otherwise, please try again.
case 10929:
// SQL Error Code: 10928
// Resource ID: %d. The %s limit for the database is %d and has been reached. For more information,
// see http://go.microsoft.com/fwlink/?LinkId=267637.
case 10928:
// SQL Error Code: 10060
// A network-related or instance-specific error occurred while establishing a connection to SQL Server.
// The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server
// is configured to allow remote connections. (provider: TCP Provider, error: 0 - A connection attempt failed
// because the connected party did not properly respond after a period of time, or established connection failed
// because connected host has failed to respond.)"}
case 10060:
// SQL Error Code: 10054
// A transport-level error has occurred when sending the request to the server.
// (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.)
case 10054:
// SQL Error Code: 10053
// A transport-level error has occurred when receiving results from the server.
// An established connection was aborted by the software in your host machine.
case 10053:
// SQL Error Code: 1205
// Deadlock
case 1205:
// SQL Error Code: 233
// The client was unable to establish a connection because of an error during connection initialization process before login.
// Possible causes include the following: the client tried to connect to an unsupported version of SQL Server;
// the server was too busy to accept new connections; or there was a resource limitation (insufficient memory or maximum
// allowed connections) on the server. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by
// the remote host.)
case 233:
// SQL Error Code: 121
// The semaphore timeout period has expired
case 121:
// SQL Error Code: 64
// A connection was successfully established with the server, but then an error occurred during the login process.
// (provider: TCP Provider, error: 0 - The specified network name is no longer available.)
case 64:
// DBNETLIB Error Code: 20
// The instance of SQL Server you attempted to connect to does not support encryption.
case 20:
    return true;
// This exception can be thrown even if the operation completed successfully, so it's safer to let the application fail.
// DBNETLIB Error Code: -2
// Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. The statement has been terminated.
//case -2: