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Presently, a rename/delete operation can become prohibitively expensive for such directories which have large sub-trees/sub-paths. Ozone does rename/delete each and every sub-file & sub-dir under the given directory via multiple RPC calls to OM thus makes it very expensive. Also, rename and delete doesn't guarantee the atomicity.

The prefix based FileSystem optimization idea allows to perform rename, delete of any directory in a deterministic/constant time atomically. Now, ozone performs rename/delete operations in a single RPC call by sending only the given directory to OM. It will finish rename, delete operations with O(1) complexity. Also, makes it possible to support atomic rename/delete of any directory at any level in the namespace.

Git Branch:

Implementing this in a separate feature HDDS-2939 branch. Thanks to all contributors/reviewers.

How to enable prefix based optimization feature:

Following are the set of configurations to be configured in 'ozone-default.xml' to enable this feature. By default the feature will be turned OFF.

An example of ozone-site.xml

<configuration>
  <property>
    <name>ozone.om.enable.filesystem.paths</name>
    <value>true</value>
  </property>
 
  <property>
    <name>ozone.om.metadata.layout</name>
    <value>prefix</value>
  </property>
 
</configuration>

Related documents

Branch merge checklist

1. builds/intermittent test failures

TODO

2. documentation

TODO

3. design, attached the docs

TODO

4. s3 compatibility

TODO

5. docker-compose / acceptance tests

TODO

6. support of containers / Kubernetes:

TODO

7. coverage/code quality:

TODO

8. build time

TODO

9. possible incompatible changes/used feature flag: 

TODO

10. third party dependencies/licence changes:

TODO

11. performance

Done testing to evaluate the performance of delete, rename operations in feature branch vs master code base. Following charts capturing the directory delete and rename operations execution time shows that, feature branch has a very significant performance gain compared to the master.

Ran freon 'dtsg' dfs tree generator benchmark test in a single node cluster. V0 represents master code and V1 represents feature branch. Please refer to the Jira document for more details.


12. security considerations

TODO



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