[HDFS-4452] getAdditionalBlock() can create multiple blocks if the client times out and retries.

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.0.2-alpha
• Fix Version/s: 2.0.3-alpha
• Component/s: namenode
• Target Version/s: 2.0.3-alpha
• Hadoop Flags: Reviewed
• Assignee: Konstantin Shvachko
• Reporter: Konstantin Shvachko
• Created: 29/Jan/13 19:46
• Updated: 25/Nov/20 19:30
• Resolved: 02/Feb/13 02:11

Description

HDFS client tries to addBlock() to a file. If NameNode is busy the client can timeout and will reissue the same request again. The two requests will race with each other in FSNamesystem.getAdditionalBlock(), which can result in creating two new blocks on the NameNode while the client will know of only one of them. This eventually results in NotReplicatedYetException because the extra block is never reported by any DataNode, which stalls file creation and puts it in invalid state with an empty block in the middle.

Issue Links

• duplicates: HDFS-4212 NameNode can't differentiate between a never-created block and a block which is really missing
• relates to: HDFS-4208 NameNode could be stuck in SafeMode due to never-created blocks
• relates to: HDFS-3031 HA: Fix complete() and getAdditionalBlock() RPCs to be idempotent.