CosmosDB bulk upsert extremly slow

Below is how I am using the bulk upsert feature in ComosDB. This code is extremely slow even for 15 documents.

var container = _database.GetContainer(collectionName);
            var cts = new List<Task>();
            foreach (var d in documents)
            {
                var t = container.UpsertItemAsync(d,
                    new PartitionKey(d.GetPartitionKey())
                );

                cts.Add(t);
            }
            await Task.WhenAll(cts);

[bartelink]

Thanks for being patient, will do (and apologies for not reading the answers you provided in the thread distinguishing between and referencing docs for Batch vs Bulk).

[j82w]

This is a good article explaining Cosmos DB partitioning: https://docs.microsoft.com/en-us/azure/cosmos-db/partitioning-overview

If it’s only 100 documents then doing individual read items is the recommend way. The SDK is thread safe so you can send multiple requests in parallel. Once the SDK connects to a single physical machine it will reuse the connection for future requests. Using the Benchmark project on Linux VM with 4 cores we are able to get over 10,000 request per a second.