RU Consumption is Unaffected when using Gateway Cache and Consistency Level Session

Describe the bug Using Microsoft.Azure.Cosmos version 3.23.0-preview, when the CosmosClient is generated if it uses CosmosClientOptions.ConsistencyLevel = ConsistencyLevel.Session duplicate queries will not reduce the RU cost whatsoever, however it will reduce the RU cost to 0 if using ConsistencyLevel.Eventual.

To Reproduce Create a CosmosClient pointing to a CosmosDB resource with gateway caching enabled with the following options:

new CosmosClient({yourUri},
    {yourAuthKey},
    new CosmosClientOptions
    {
	    ConnectionMode = ConnectionMode.Gateway,
	    ConsistencyLevel = ConsistencyLevel.Session
    });

Then write a query against any database and container. Run the query more than once and check the FeedResponse.RequestCharge every time. Every time the query is executed RUs are charged against the account. Now create a ComosClient with the following options:

new CosmosClient({yourUri},
    {yourAuthKey},
    new CosmosClientOptions
    {
	    ConnectionMode = ConnectionMode.Gateway,
	    ConsistencyLevel = ConsistencyLevel.Eventual
    });

Repeat the steps above and you’ll see that after the first request the RU charge drops down to 0 for subsequent requests.

Expected behavior According to this documentation: https://docs.microsoft.com/en-us/azure/cosmos-db/how-to-configure-integrated-cache#adjust-request-consistency

The integrated cache should be utilized if the ConsistencyLevel is Eventual or Session

Actual behavior The integrated Cache appears to be being bypassed when the ConsistencyLevel is Session

Environment summary SDK Version: 3.23.0-preview OS Version Windows

Additional context Additionally, you may want to consider not exposing CosmosClient.ClientOptions.ConnectionMode and CosmosClient.ClientOptions.ConsistencyLevel because if those variables are not set in the constructor for CosmosClient they seem to be ignored and that can be quite confusing.

[robsierra]

I will email you our CosmosDB name but I’m including the sample code here for reference in the event others experience this issue.

async Task Main()
{
	var client = new CosmosClient("{connectionUrl}",
		"{authKey}",
		new CosmosClientOptions
		{
			ConnectionMode = ConnectionMode.Gateway,
			ConsistencyLevel = ConsistencyLevel.Session
		});


	Database database = client.GetDatabase("{dbName}");
	Container container = database.GetContainer("{containerName}");

	double totalRU = 0;
	var cmd = "select * from T where T.Timestamp > '2021-11-10'";
	var query = new QueryDefinition(cmd);
	using (FeedIterator<dynamic> feedIterator = container.GetItemQueryIterator<dynamic>(query,
	requestOptions: new QueryRequestOptions
	{
		// Only available using preview sdk
		DedicatedGatewayRequestOptions = new DedicatedGatewayRequestOptions
		{
			MaxIntegratedCacheStaleness = TimeSpan.FromMinutes(30),
			
		}
	}))
	{
		while (feedIterator.HasMoreResults)
		{
			FeedResponse<dynamic> response = await feedIterator.ReadNextAsync();
			totalRU += response.RequestCharge;
		}
	}
	totalRU.Dump();
}

This is run in Linqpad, if you run the above code twice you will be charged RU’s both times, but if you set the consistencyLevel to eventual and run the code twice you will only be charged for the first request.

[robsierra]

@ealsur I see, that does make sense and thank you for the explanation. If that is the case I would appreciate any help directing me to whom I should make a bug report.