CODEWITHSUNDEEP
azure-cosmosdb
bwwilliam
bwwilliam

Reputation: 101

Cosmos DB ChangeFeed Exception Handling

With Cosmos DB ChangeFeed, can anyone please provide some help with exception handling? Let's say if I have 10 documents in the change feed, I have a loop to iterate through the documents one by one. Let's assume if there was an exception happened after the 5th document that is processed. What is going to happen with the changefeed? So far, it looks to me that the entire changefeed is swallowed, i.e. the rest documents after the exception are gone.

I am just wondering what is the backout strategy on this? Is there a way I can completely backout the entire batch so I do not loose any changes.

Upvotes: 2

Views: 2213

Answers (2)

Pankaj Rawat
Pankaj Rawat

Reputation: 4573

Recommendation from MS, to add try-catch in your CosmosDB trigger function. If any document throw exception you have to store in place.

Once you will start storing failed messages in some location, you have to build metrics, alerts and re-process strategy.

Below is my strategy to handle this scenario. My One function listing to DB changefeed and pushing data into "Topic" (without any process). I created multiple subscriptions so each subscription maintain own dead-letter queue.

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Upvotes: 0

Rafat Sarosh
Rafat Sarosh

Reputation: 945

It is an old question, but hopefully other may find it useful.

To handle the error, the recommended pattern is to wrap your code with try-catch. Catch the error and put that document on a queue (dead-letter). Have a separate program to deal with those document which produced the error. This way if you have 100-document batch, and just one document failed, you do not have to throw away the whole batch.

Second reason is if you can keep getting those documents from Change Feed then you may lose the last snapshot on the document. Change Feed keeps only one last version of the document, in between other processes can come and change the document.

As you keep fixing your code, you will soon find no documents on dead-letter queue.

Azure Function is automatically called by Change Feed system. If you want to roll back the Change Feed and control every aspect of it, you should consider using Change processor Feed SDK.

Upvotes: 1

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