[HDFS-12906] hedged point read in DFSInputStream sends only 1 hedge read request

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: hdfs-client
• Assignee: Tao Zhang
• Reporter: Tao Zhang
• Created: 06/Dec/17 22:05
• Updated: 16/Apr/18 01:11

Description

Hedged point read is handled in DFSInputStream.hedgedFetchBlockByteRange(). It calls "getFirstToComplete()" to get the 1st returned result after sending out hedge read requests. But since "getFirstToComplete()" uses "CompletionService.take()" which is a endlessly blocking operation. It will wait for 1 result after sending only 1 hedge read request.

It could be changed to wait for a specific timeout (instead of infinite timeout) and starting another hedge read request.