[POC] HDDS-3915. Simple trash emptier on OM

[smengcl]

What changes were proposed in this pull request?

Implementation something similar to HDFS's NameNode#startTrashEmptier in OzoneManager to enable automatic trash clean up.

Pros:

• Easiest to implement. Uses Hadoop trash policy and FS getTrashRoots impl.
• OM needs to load two client FS jars. But really just uses the getTrashRoots() impl.

Cons:

• Before HDDS-2939 Ozone FS namespace is done, renaming is expensive if there are a lot of files in the Current checkpoint.
  • This con can be overcome by overriding TrashPolicyDefault (specify custom fs.trash.classname) on the client & OM: client directly create a timestamp every time it deletes files to trash, eliminating renaming; OM periodically checks for older timestamps and removes them.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-3915

How was this patch tested?

Tested manually so far. Steps:

$ mvn clean install -Pdist -DskipTests -e -Dmaven.javadoc.skip=true -DskipShade
$ cd hadoop-ozone/dist/target/ozone-*-SNAPSHOT/compose/ozone
$ vi docker-config
# Add two lines of config:
CORE-SITE.XML_fs.defaultFS=ofs://om
CORE-SITE.XML_fs.trash.interval=1

Note on the configs:
fs.defaultFS has to be picked up by OM as it resolves this path to be the FS for trash cleanup thread.
fs.trash.interval is also picked up by OM as fs.trash.checkpoint.interval in this case.
fs.trash.interval also needs to be picked up by the client to enable move to trash.

Spin up the docker-compose cluster:

$ docker-compose up -d
# Wait for ~30s for OM to init and start. Then run the below command to see that the cleaner thread is started
$ docker-compose logs om | grep fs.TrashPolicyDefault
om_1        | 2020-07-09 05:19:53,348 [Listener at om/9862] INFO fs.TrashPolicyDefault: The configured checkpoint interval is 0 minutes. Using an interval of 1 minutes that is used for deletion instead
om_1        | 2020-07-09 05:19:53,348 [Listener at om/9862] INFO fs.TrashPolicyDefault: Namenode trash configuration: Deletion interval = 1 minutes, Emptier interval = 1 minutes.

Now let's use the client to move a file to trash. fs.trash.interval=1 (1 min for testing purpose) is configured on both OM and client in the container.

$ docker-compose exec om /bin/bash
$ ozone fs -mkdir -p ofs://om/volume1/bucket2/dir3
2020-07-09 05:33:01,592 [main] INFO rpc.RpcClient: Creating Volume: volume1, with hadoop as owner.
2020-07-09 05:33:01,778 [main] INFO rpc.RpcClient: Creating Bucket: volume1/bucket2, with Versioning false and Storage Type set to DISK and Encryption set to false
$ ozone fs -touch ofs://om/volume1/bucket2/dir3/key5
$ ozone fs -rm ofs://om/volume1/bucket2/dir3/key5
2020-07-09 05:33:42,721 [main] INFO Configuration.deprecation: io.bytes.per.checksum is deprecated. Instead, use dfs.bytes-per-checksum
2020-07-09 05:33:42,934 [main] INFO fs.TrashPolicyDefault: Moved: 'ofs://om/volume1/bucket2/dir3/key5' to trash at: ofs://om/volume1/bucket2/.Trash/hadoop/Current/volume1/bucket2/dir3/key5

In a minute OM trash cleanup thread will checkpoint the trash:

2020-07-09 05:34:00,055 [Trash Emptier] INFO fs.TrashPolicyDefault: TrashPolicyDefault#deleteCheckpoint for trashRoot: ofs://om/volume1/bucket2/.Trash/hadoop
2020-07-09 05:34:00,173 [Trash Emptier] INFO fs.TrashPolicyDefault: Created trash checkpoint: /volume1/bucket2/.Trash/hadoop/200709053400

Confirm the checkpoint on the client:

$ ozone fs -ls /volume1/bucket2/.Trash/hadoop/
Found 1 items
drwxrwxrwx   - hadoop hadoop          0 2020-07-09 05:34 /volume1/bucket2/.Trash/hadoop/200709053400

In the next minute the checkpoint is deleted:

2020-07-09 05:35:00,035 [Trash Emptier] INFO fs.TrashPolicyDefault: TrashPolicyDefault#deleteCheckpoint for trashRoot: ofs://om/volume1/bucket2/.Trash/hadoop
2020-07-09 05:35:00,096 [Trash Emptier] INFO fs.TrashPolicyDefault: Deleted trash checkpoint: /volume1/bucket2/.Trash/hadoop/200709053400

[elek]

/pending draft PR without activity

[github-actions]

Marking this issue as un-mergeable as requested.

Please use /ready comment when it's resolved.

draft PR without activity

[smengcl]

Closing this PR as this is only a POC and won't be ever merged.