Patterns to azure idempotent operations?

anybody know patterns to design idempotent operations to azure manipulation, specially the table storage开发者_如何学编程? The more common approach is generate a id operation and cache it to verify new executions, but, if I have dozen of workers processing operations this approach will be more complicated. :-))

Thank's

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Ok, so you haven't provided an example, as requested by knightpfhor and codingoutloud. That said, here's one very common way to deal with idempotent operations: Push your needed actions to a Windows Azure queue. Then, regardless of the number of worker role instances you have, only one instance may work on a specific queue item at a time. When a queue message is read from the queue, it becomes invisible for the amount of time you specify.

Now: a few things can happen during processing of that message:

• You complete processing after your timeout period. When you go to delete the message, you get an exception.
• You realize you're running out of time, so you increase the queue message timeout (today, you must call the REST API to do this; one day it'll be included in the SDK).
• Something goes wrong, causing an exception in your code before you ever get to delete the message. Eventually, the message becomes visible in the queue again (after specified invisibility timeout period).
• You complete processing before the timeout and successfully delete the message.

That deals with concurrency. For idempotency, that's up to you to ensure you can repeat an operation without side-effects. For example, you calculate someone's weekly pay, queue up a print job, and store the weekly pay in a Table row. For some reason, a failure occurs and you either don't ever delete the message or your code aborts before getting an opportunity to delete the message.

Fast-forward in time, and another worker instance (or maybe even the same one) re-reads this message. At this point, you should theoretically be able to simply re-perform the needed actions. If this isn't really possible in your case, you don't have an idempotent operation. However, there are a few mechanisms at your disposal to help you work around this:

• Each queue message has a DequeueCount. You can use this to determine if the queue message has been processed before and, if so, take appropriate action (maybe examine the Table row for that employee, for example).
• Maybe there are stages of your processing pipeline that can't be repeated. In that case: you now have the ability to modify the queue message contents while the queue message is still invisible to others and being processed by you. So, imagine appending something like |SalaryServiceCalled . Then a bit later, appending |PrintJobQueued and so on. Now, if you have a failure in your pipeline, you can figure out where you left off, the next time you read your message.

Hope that helps. Kinda shooting in the dark here, not knowing more about what you're trying to achieve.

EDIT: I guess I should mention that I don't see the connection between idempotency and Table Storage. I think that's more of a concurrency issue, as idempotency would need to be dealt with whether using Table Storage, SQL Azure, or any other storage container.

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I believe you can use Reply log storage way to solve this problem