YARN_LOCAL_DIR could be configured with multiple dirs. This will YARN to choose one dir out of a set of good dirs in random way. YARN use roulette mode selection to ensure that all dirs used in LOCAL_DIR gets filled in similar way. When YARN wants to get a file from the local dir, we know that suffix part of the file (file name etc), now this will be searched in all configured dirs till we get a one.
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