For a snapshottable directory,
the path component ".snapshot" is used for accessing its snapshots.
Suppose /foo is a snapshottable directory,
/foo/bar is a file/directory in /foo,
and /foo has a snapshot s0.
Then, the path /foo/.snapshot/s0/bar
refers to the snapshot copy of /foo/bar.
The usual API and CLI can work with the ".snapshot" paths.
The following are some examples:
Listing all the snapshots under a snapshottable directory:
hadoop dfs -ls /foo/.snapshotListing the files in snapshot
s0:hadoop dfs -ls /foo/.snapshot/s0Copying a file from snapshot
s0:hadoop dfs -cp /foo/.snapshot/s0/bar /tmp
The name ".snapshot" is now a reserved file name in HDFS so that users cannot create a file/directory with ".snapshot" as the name. If ".snapshot" is used in a previous version of HDFS, it must be renamed before upgrade; otherwise, upgrade will fail.
