Support for CountAsync()

Is your feature request related to a problem? Please describe. In version 2.x of the SDK, we were able to execute asynchronous calls for determining the count of a IQueryable. It seems like you can only perform this in a synchronous fashion in the current version of the SDK.

Describe the solution you’d like Support the CountAsync() LINQ syntax

Describe alternatives you’ve considered None, there doesn’t appear to be support for this currently.

[wahyuen]

@j82w Thanks for the response. We had a quick test with your above suggestion and had some interesting observations to share.

Test Scenarios:

• DocumentClient with synchronous Count call
• DocumentClient with asynchronous CountAsync call
• CosmosClient with sychronous Count call
• CosmosClient with above mentioned asychronous iterator async pattern Microsoft.Azure.DocumentDB.Core 2.5.1 Microsoft.Azure.Cosmos 3.0.0

Test Code

var feedOptions = new FeedOptions
{
	MaxBufferedItemCount = -1,
	MaxItemCount = -1,
	MaxDegreeOfParallelism = -1,
	EnableCrossPartitionQuery = true
};

var documentClientSyncCount = documentClient.CreateDocumentQuery<Image>(uri, feedOptions)
	.Count(x => x.Investigations.Contains(investigationKey));

Console.WriteLine($"DocumentClient.Count: {documentClientSyncCount} - {watch.Elapsed.TotalMilliseconds:0}ms");

watch.Restart();

var documentClientAsyncCount = await documentClient.CreateDocumentQuery<Image>(uri, feedOptions)
	.Where(x => x.Investigations.Contains(investigationKey)).CountAsync();

Console.WriteLine($"DocumentClient.CountAsync: {documentClientAsyncCount} - {watch.Elapsed.TotalMilliseconds:0}ms");

watch.Restart();

var queryRequestOptions = new QueryRequestOptions
{
	MaxBufferedItemCount = -1,
	MaxConcurrency = -1,
	MaxItemCount = -1
};

var cosmosSyncCount = imagesContainer.GetItemLinqQueryable<Image>(true, queryRequestOptions).Count(x => x.Investigations.Contains(investigationKey));
Console.WriteLine($"CosmosClient.Count: {cosmosSyncCount} - {watch.Elapsed.TotalMilliseconds:0}ms");

watch.Restart();

var cosmosAsyncCount = 0;
var countIterator = imagesContainer.GetItemLinqQueryable<Image>(false, queryRequestOptions).Where(x => x.Investigations.Contains(investigationKey))
	.ToFeedIterator();

while (countIterator.HasMoreResults)
{
	var response = await countIterator.ReadNextAsync();

	cosmosAsyncCount += response.Resource.Count();
}

Console.WriteLine($"CosmosClient.CountAsync: {cosmosAsyncCount} - {watch.Elapsed.TotalMilliseconds:0}ms");

Results

DocumentClient.Count: 1763 - 2035ms
DocumentClient.CountAsync: 1763 - 2779ms
CosmosClient.Count: 1763 - 955ms
CosmosClient.CountAsync: 1763 - 8112ms

Observations

• surprisingly, even the DocumentClient.CountAsync() seems to be slower than the sync version
• the above mentioned iterator pattern seems to be significantly worse in performance than the sync version
• the current implemenation of Count on CosmosClient seems to be the faster of all so far!!

We ran in to this issue as we are attempting to port our current 2.x SDK code to the new 3.x SDK. From this perspective, we have a large number of cases where we wish to perform various counts to a number of collections and we will often firing these off using CountAsync and simply execute a await Task.WhenAll(tasks) call to wait for them to all return.

If it was possible, we’d love to see your proposal of CountAsync extension method, as we believe this is the most idiomatic syntax given where previous developers are migrating from. If the SDK could combine the performance of the current implementation of Count in an asynchronous manner, we would be very happy campers 😃

[mark-manticore]

With the newly released 3.1 SDK I’m now able to work around this issue with the following code.

var requestOptions = new QueryRequestOptions();
requestOptions.EnableScanInQuery = true;

var queryDefinition = _container.GetItemLinqQueryable<T>().Where(predicate).ToQueryDefinition();
var queryText = queryDefinition.QueryText.Replace("VALUE root", "VALUE COUNT(1)", StringComparison.OrdinalIgnoreCase);
var queryIterator = _container.GetItemQueryIterator<int>(queryText, null, requestOptions);
var response = await queryIterator.ReadNextAsync();
return response.Resource.FirstOrDefault();