A common yet one of the most important DataStage interview questions for experienced, don't miss this one. InfoSphere DataStage automatically buffers links for certain stages. Its main purpose is to prevent deadlock conditions (where a stage cannot read its input because a previous stage in the job cannot write to its output).  Jobs with fork joins can lead to deadlock conditions. Here, the stage has two output connections whose data paths are merged later in the job. A situation can arise where all stages in the flow are waiting for other stages to read or write, so none of them can continue. No error or warning message is issued if a deadlock occurs. Your work will wait forever for input.  InfoSphere DataStage automatically inserts buffering into job flows containing branch joins that can lead to deadlock conditions. In most cases, you do not need to change the default buffering implemented by InfoSphere DataStage.