Highest response ratio next

Highest response ratio next (HRRN) scheduling is a non-preemptive discipline. It was developed by Brinch Hansen as modification of shortest job next or shortest job first (SJN or SJF) to mitigate the problem of process starvation. In HRRN, the next job is not that with the shortest estimated run time, but that with the highest response ratio defined as

${\displaystyle response\ ratio={\frac {waiting\ time\ of\ a\ process\ so\ far+estimated\ run\ time}{estimated\ run\ time}}=1+{\frac {waiting\ time\ of\ a\ process\ so\ far}{estimated\ run\ time}}}$

This means, the jobs that have spent a long time waiting compete against those estimated to have short run times. As you can see in the above equation of response ratio, if the waiting time of a process increases, its response ratio increases making the long-awaited process to execute next. So, this algorithm solves the starvation problem that exists in SJN scheduling algorithm.