Weird Hystrix Behaviour being observed.

[karanpreet8082]

Hey,

Facing threadpool rejections even with under-utilised threadpool

Scenario :
With a concurrency of 64, i have configured my hystrix commands, while this works for all my commands, but for a certain command, occasionally threadpool rejections are encountered.

This command is configured to concurrency of 64 and the utilisation of the threadpool for this command is near 17-18. Utilisation never crosses 20 but still with this under-utilisation, rejections are observed.

Configuration :

semaphoreIsolation : false
concurrency : 64
maxRequestQueueSize : 128
dynamicRequestQueueSize : 16

What could be the possible thing causing this ??