map task's input split are running other map task

Vote count:

0

i am unable to understand this statement in Hadoop - Definitive Guide 3rd Edition ( Page 31) "Sometimes, However, all the three nodes hosting the HDFS block replicas for a map task's input split are running other map tasks so the job scheduler will look for a free map slot on a node in the same Rack as one of the blocks. very occasionally even this is not possible so an off rack node is used which results in an inter-rack network transfer." ,

my question is

1) i am unable to get the full context of this statement

2) does this mean if an input split is accquired by other map task say (running Map Task), it say (waiting Map Task) will look for other replica of same split ? will "Waiting Map task" does not use the output of the "Running Map Task", if map logic is same in Running Map Task and Waiting Map Task

asked 56 secs ago

Sathiya Moorthy

1

map task's input split are running other map task