CreateDocumentCollectionIfNotExistsAsync does not always work

Question

I am trying to create a collection if it does not exist.

First, I create my DocumentClient by:

public DocumentClient CreateClient(ConnectionPolicy connectionPolicy = null)
{
   return new DocumentClient(new Uri(this.AccountEndpoint), this.AccountKey, connectionPolicy);
}

Now that I have my document client (let's call it documentDbClient), I attempt to use CreateDocumentCollectionIfNotExistsAsync:

var documentDbClient = dbConnection.CreateClient();

await documentDbClient.CreateDocumentCollectionIfNotExistsAsync(UriFactory.CreateDatabaseUri("mydatabase"),
            new DocumentCollection { Id = "testcollection" });

Now, I would expect this to create a collection named testcollection under my database named mydatabase. However, nothing happens. No collection is created, no exceptions are thrown.

I thought perhaps it was just slow, and so I waited 30 minutes and went back to the portal to see if my collection had been made...

It hadn't.

What is wrong?

UPDATE

Okay, so I have discovered that if I change the name of the collection that I am attempting to create, it works. I have previously created and deleted the collection many times and now it appears that Azure is failing to create it 90% of the time.

Answer 1

So, you're likely running into a throttling situation when repeatedly creating and destroying collections. Here's an excerpt from the Table API section of the FAQ (which applies equally to document collections):

The rapid rate of creation of tables is detected and throttled. We recommend that you look at the rate of creation of tables and lower it to less than 5 per minute.

The current throttle rate is 5 creates / minute. So, for a unit-testing scenario, you'd need to work around this (e.g. keeping a collection, but just emptying its contents after each test run).

Note: I notified the product team, that the throttle mention is only in the Table API section, and to update the FAQ accordingly.

Answer 2

You should add a .Wait() to the end of database creation and then the collection creation. This will wait for both tasks to complete.

_client.CreateDatabaseIfNotExistsAsync(new Database { Id = "dbName" }).Wait();

_client.CreateDocumentCollectionIfNotExistsAsync(UriFactory.CreateDatabaseUri("dbName"), new DocumentCollection { Id = "collectionName" }).Wait();