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https://issues.apache.org/jira/browse/HDFS-16496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephen O'Donnell resolved HDFS-16496.
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Fix Version/s: 3.4.0
Resolution: Fixed
> Snapshot diff on snapshotable directory fails with not snapshottable error
> --------------------------------------------------------------------------
>
> Key: HDFS-16496
> URL: https://issues.apache.org/jira/browse/HDFS-16496
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namanode
> Affects Versions: 3.4.0
> Reporter: Stephen O'Donnell
> Assignee: Stephen O'Donnell
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.4.0
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> Running a snapshot diff against some snapshotable folders gives an error:
> {code}
> org.apache.hadoop.hdfs.protocol.SnapshotException: Directory is neither
> snapshottable nor under a snap root!
> at
> org.apache.hadoop.hdfs.server.namenode.snapshot.SnapshotManager.checkAndGetSnapshottableAncestorDir(SnapshotManager.java:395)
> at
> org.apache.hadoop.hdfs.server.namenode.snapshot.SnapshotManager.diff(SnapshotManager.java:744)
> at
> org.apache.hadoop.hdfs.server.namenode.FSDirSnapshotOp.getSnapshotDiffReportListing(FSDirSnapshotOp.java:200)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getSnapshotDiffReportListing(FSNamesystem.java:6983)
> at
> org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.getSnapshotDiffReportListing(NameNodeRpcServer.java:1977)
> at
> org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.getSnapshotDiffReportListing(ClientNamenodeProtocolServerSideTranslatorPB.java:1387)
> at
> org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
> at
> org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:533)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:1070)
> at org.apache.hadoop.ipc.Server$RpcCall.run(Server.java:989)
> at org.apache.hadoop.ipc.Server$RpcCall.run(Server.java:917)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:422)
> at
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1898)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2894)
> {code}
> This is caused by HDFS-15483 (in order snapshot delete), and the issue is in
> the following method in SnapshotManager:
> {code}
> public INodeDirectory getSnapshottableAncestorDir(final INodesInPath iip)
> throws IOException {
> final String path = iip.getPath();
> final INode inode = iip.getLastINode();
> final INodeDirectory dir;
> if (inode instanceof INodeDirectory) { // THIS SHOULD BE TRUE - change to
> inode.isDirectory()
> dir = INodeDirectory.valueOf(inode, path);
> } else {
> dir = INodeDirectory.valueOf(iip.getINode(-2), iip.getParentPath());
> }
> if (dir.isSnapshottable()) {
> return dir;
> }
> for (INodeDirectory snapRoot : this.snapshottables.values()) {
> if (dir.isAncestorDirectory(snapRoot)) {
> return snapRoot;
> }
> }
> return null;
> }
> {code}
> After adding some debug, I found the directory which is the snapshot root is
> not an instance of INodeDirectory, but instead is an
> "INodeReference$DstReference". I think the directory becomes an instance of
> this class, if the directory is renamed and one of its children has been
> moved out of another snapshot.
> The fix is simple - just check `inode.isDirectory()` instead.
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