title: Why is `fixed_auto_queue_size` in Elasticsearch deprecated?
body: <p>I'm trying to configure the threadpool of my Elasticsearch cluster. The <a href="https://www.elastic.co/guide/en/elasticsearch/reference/7.17/modules-threadpool.html#:%7E:text=Deprecated%20in%207.7.&amp;text=The%20experimental%20fixed_auto_queue_size%20thread%20pool,will%20be%20removed%20in%208.0." rel="nofollow noreferrer"><code>fixed_auto_queue_size</code></a> looks a neat idea as it adjusts its maximum queue size based on Little's Law. However, this feature is deprecated in ES 7.7.0. Does anyone know why the feature is deprecated? I'm interested in practical issues that this configuration will have. Is it because Little's Law assumes a stable system? If so, what could go wrong when the assumption is not true any more?</p>