FIFO scheduler

The FIFO scheduler uses the simple strategy of first come first serve. Memory will be allocated to applications based on the sequence of request time, which means the first application in the queue will be allocated the required memory, then the second, and so on. In case memory is not available, applications have to wait for sufficient memory to be available for them to launch their jobs. When the FIFO scheduler is configured, YARN will make a queue of requests and add applications to the queue, then launch applications one by one.