TCP connections much higher than GatewayModeMaxConnectionLimit

Describe the bug In Gateway mode with GatewayModeMaxConnectionLimit around 500, TCP connections used by our Azure App service towards our Cosmos DB goes far beyond the 500 limit.

To Reproduce

1. We got a single CosmosClient built like that (new CosmosClientBuilder(endpoint, authKey).WithConnectionModeGateway(500).Build())
2. We use a single Container, hence a single database and collection. Code looks like that client.GetContainer(config.OurDatabase, config.OurDataCollection)
3. From there, we use the container in 2 ways. Either we read from with container.GetItemQueryStreamIterator or write to with await container.UpsertItemStreamAsync

Our app is living alone on an app service plan (“server”)

Expected behavior We expect to have at most 500 TCP connections towards our Cosmos DB but under some load (5K Cosmos request under 1 minute) we get to the app service’s TCP connections limit (in our case, ~4K)

Actual behavior We got many SocketExceptions resulting in faulted Cosmos Queries.

One of our TCP peak problems:

Environment summary SDK Version: 3.5.0 OS Version: Windows App service P2v2

Thanks a lot Phil

[j82w]

This PR https://github.com/Azure/azure-cosmos-dotnet-v3/pull/1548 needs to go in first. Then this fix can be added.

[j82w]

@jesuissur thanks for investigating. I’ll try to get a PR out with a fix before the next release.