WCF服务：丢弃的连接处理

Question

Have a WCF Service being called to update records in the database. If the connection is broken, the service will continue to process the data, but the client won't know of the results. IE the processing could have succeeded or failed; the client doesn't know if it should resend the data.

Typical example would be a bank deposit. An ATM takes a deposit and makes a WCF call to update the customer's account. The connection is dropped, leaving the ATM uncertain as to whether the deposit was processed or not. If it wasn't, and the ATM doesn't resend, the customer doesn't have the money in his account. If the ATM resends, but the deposit was processed, he'll have two deposits.

Enabling transactions on the WCF Service call seems the thing to do, but can they handle a dropped connection? IE the client can roll back the transaction if it loses connection to the server, but how would the server know about the rollback if the client isn't connected?

Answer 1

It seems that any way you look at it, there is a possible issue for serious catastrophic failure.

Assuming that you are using async client calls and/or the ammount of processing being done on the service side is relatively large. If in the span of the ammount of time, the connection to the service from the client is severed, there is no way for the client to know what state the service was last left in. If it was mid-transaction, the service side transaction will be cancled automatically... if it was post-transaction then your work is done... but in both situations the client will "never know".

Theoretically... (and don't quote me on this, but it SOUNDS like a logical scenario) if an ATM loses connection in the process of doing a deposit... I believe (and like I said don't quote me on this) that the ATM itself keeps a list of transaction in memory so that in a situation where a transaction fails, once the connection is re-established it can check itself and verify if the transaction was actually completed. (If it in reality doesn't do this... I would be a bit concerned personally).

To make a long story short... I believe the only thing you can do in this scenario is to have the client side keep some sort of checksum which would match with the service side so that if a connection failure occurred, when the connection was re-established, it would be able to check against the service to see if the transaction did in fact complete or not.

Answer 2

我将使用BizTalk之类的EAI提供程序来协调WCF服务，并为服务公开的每个操作设置补偿操作，以便在发生故障时可以执行回滚。