Kihwal Lee created HDFS-10763:
---------------------------------
Summary: Open files can leak permanently due to inconsistent lease
update
Key: HDFS-10763
URL: https://issues.apache.org/jira/browse/HDFS-10763
Project: Hadoop HDFS
Issue Type: Bug
Affects Versions: 2.6.4, 2.7.3
Reporter: Kihwal Lee
Priority: Critical
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
{noformat}
...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)
...
{noformat}
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.
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