Using Ktor and Kotlin 1.5 to implement a REST service backed by Netty. A couple of things about this service:

1. "Work" takes non-trivial amount of time to complete.
2. A unique client endpoint sends multiple requests in parallel to this service.
3. There are only a handful of unique client endpoints.

The service is not scaling as expected. We ran a load test with parallel requests coming from a single client and we noticed that we only have two threads on the server actually processing the requests. It's not a resource starvation problem - there is plenty of network, memory, CPU, etc. and it doesn't matter how many requests we fire up in parallel - it's always two threads keeping busy, while the others are sitting idle.

Is there a parameter we can configure to increase the number of threads available to process requests for specific endpoints?

CodePudding user response：

Netty use what is called Non-blocking IO model (http://tutorials.jenkov.com/java-concurrency/single-threaded-concurrency.html).

In this case you have only a single thread and it can handle a lot of sub-processes in parallel, as long as you follow best practices (not blocking the main thread event loop).

CodePudding user response：

You might need to check the following configuration options for Netty https://ktor.io/docs/engines.html#configure-engine

connectionGroupSize = x
workerGroupSize = y
callGroupSize = z

Default values usually are set rather low and tweaking them could be useful for the time-consuming 'work'. The exact values might vary depending on the available resources.