[HDFS-10763] Open files can leak permanently due to inconsistent lease update

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.7.3, 2.6.4
• Fix Version/s: 2.8.0, 2.9.0, 2.6.5, 2.7.4, 3.0.0-alpha1
• Target Version/s: 2.6.5, 2.7.4
• Hadoop Flags: Reviewed
• Assignee: Kihwal Lee
• Reporter: Kihwal Lee
• Created: 15/Aug/16 16:55
• Updated: 05/Mar/18 18:14
• Resolved: 18/Aug/16 21:43

Description

This can heppen during commitBlockSynchronization() or a client gives up on closing a file after retries.
From finalizeINodeFileUnderConstruction(), the lease is removed first and then the inode is turned into the closed state. But if any block is not in COMPLETE state,
INodeFile#assertAllBlocksComplete() will throw an exception. This will cause the lease is removed from the lease manager, but not from the inode. Since the lease manager does not have a lease for the file, no lease recovery will happen for this file. Moreover, this broken state is persisted and reconstructed through saving and loading of fsimage. Since no replication is scheduled for the blocks for the file, this can cause a data loss and also block decommissioning of datanode.

The lease cannot be manually recovered either. It fails with

...AlreadyBeingCreatedException): Failed to RECOVER_LEASE /xyz/xyz for user1 on
 0.0.0.1 because the file is under construction but no leases found.
	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.recoverLeaseInternal(FSNamesystem.java:2950)
...

When a client retries close(), the same inconsistent state is created, but it can work in the next time since checkLease() only looks at the inode, not the lease manager in this case. The close behavior is different if HDFS-8999 is activated by setting dfs.namenode.file.close.num-committed-allowed to 1 (unlikely) or 2 (never).

In principle, the under-construction feature of an inode and the lease in the lease manager should never go out of sync. The fix involves two parts.
1) Prevent inconsistent lease updates. We can achieve this by calling removeLease() after checking the block state.
2) Avoid reconstructing inconsistent lease states from a fsimage. 1) alone does not correct the existing inconsistencies surviving through fsimages. This can be done during fsimage loading time by making sure a corresponding lease exists for each inode that are with the underconstruction feature.

Issue Links

• is duplicated by: HDFS-10992 file is under construction but no leases found