[HDFS-2751] Datanode drops OS cache behind reads even for short reads

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.23.0, 2.0.0-alpha
• Fix Version/s: 0.23.1, 1.1.0
• Component/s: datanode
• Target Version/s: 0.23.0, 1.1.0
• Hadoop Flags: Reviewed
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 04/Jan/12 23:52
• Updated: 10/Mar/15 04:35
• Resolved: 20/Jan/12 07:32

Description

HDFS-2465 has some code which attempts to disable the "drop cache behind reads" functionality when the reads are <256KB (eg HBase random access). But this check was missing in the close() function, so it always drops cache behind reads regardless of the size of the read. This hurts HBase random read performance when this patch is enabled.

Issue Links

• relates to: HDFS-2465 Add HDFS support for fadvise readahead and drop-behind