Using Hedged Reads

You can enable hedged reads if you want to increase the performance of a read operation from an HDFS block that occasionally takes a long time. This feature helps in situations where a read occasionally takes a long time rather than when there is a systemic problem.

If a read from an HDFS block is slow, the HDFS client starts up another parallel, 'hedged' read against a different block replica. The result of whichever read returns first is used, and the outstanding read is cancelled. Hedged reads can be enabled for HBase when the HFiles are stored in HDFS. This feature is disabled by default.