How Do I Disable HDFS Hedged Read on HBase?

Symptom

For MRS 3.3.1 and later versions, HDFS hedged read is enabled by default to reduce read latency and adapt to network changes. For details about this function, see Configuring HDFS Hedged Read. Table 1 describes related parameters.

**Table 1** Parameters of HDFS hedged read
Parameter	Description	Default Value	Value Range
dfs.client.hedged.read.threshold.millis	The number of milliseconds the HDFS client waits for the first byte of the first data block before deciding whether to start a hedged read	250	Greater than or equal to 1
dfs.client.hedged.read.threadpool.size	Size of the hedged read thread pool. If this parameter is set to a value greater than 0, multiple read channels are enabled.	200	Greater than or equal to 0

HDFS hedged read may cause performance deterioration when the disk I/O is high. You need to disable this function on HBase by referring to Procedure.

Procedure

Log in to FusionInsight Manager.
Choose Cluster > Service > HBase > Configurations > All Configurations. The All Configurations page is displayed.
Search for dfs.client.hedged.read.threadpool.size and change its value to 0.
Click Save.
Click Instances, select all RegionServer instances, and choose More > Instance Rolling Restart to apply the changes.