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Is CONVOY Effect possible in "Longest job first" non preemptive scheduling policy?
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Consider a set of n processes among which there are 10 longest jobs which are CPU bound and remaining (n-10) are shortest jobs which are I/O bound processes.

Consider all these processes are initially present int the Ready queue, so Longest Job First Scheduler $\textbf{(LJF)}$ will schedule all the longest job first on the CPU. Now as soon as these long jobs complete there CPU burst they will move to wait state to complete their I/O burst. Now all these short jobs will complete their CPU burst and will move to the wait state and will complete their I/O burst along with the long jobs. Once the processes completes their I/O burst they will move to ready queue. Again in the ready queue, short term scheduler will pick the longest jobs first to schedule on the CPU, so again small jobs will keep on waiting in the ready state even though they have very less CPU burst time.

So this situation will keep on rotating and due to the large burst time of the longer jobs, shorter jobs will have to wait in the ready queue in order to get completed. Thus throughput of the system decreases and also waiting time increases.

Because of the small number of long CPU bound processes all other processes are waiting which is $\text{CONVOY EFFECT}$

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