I have a java application and elasticsearch with indices of size in order of 10 gig size. There is strange scenario, which is during the night as request volume decreases response duration increases. I had checked server resources metric but nothing unusual found.

hear we have request volume diagram:

and request duration:

as you see request duration maxima exactly lies at interval of request volume minima. but when we check server resources nothing unusual can be seen:

I must mention that no special config has been set for elasticsearch and all the config has been left with default.

Also I have checked this link How does high memory pressure affect performance? but as you see server memory is far away from 75% memory usage.

I must also mention that elasticsearch is inside ceph file system