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While a Hadoop Job is running or in progress if I write something to HDFS or Hbase then will that
data be visible to all nodes in the cluster
1.)immediately?
2.)If not immediately then after how much time?
3.)Or the time really cannot be determined?
HDFS is strongly consistent, so once a write has completed successfully, the new data should be visible across all nodes immediately. Clearly the actual writing takes some time – see replication pipelining for some details on this.
This is in contrast to eventually consistent systems, where it may take an indefinite time (though often only a few milliseconds) before all nodes see a consistent view of the data.
Systems such as Cassandra have tunable consistency – each read and write can be performed at a different level of consistency to suit the operation being performed.