Merge pull request #501 from eric-wu/develop

Add metrics to dynamo workers
Improve the performance of isRoot() to constant time
Merge pull request #503 from eric-wu/release-y

Improve the performance of isRoot() to constant time
Merge branch 'release-y' into develop
Merge remote-tracking branch 'upstream/develop' into develop
Merge branch 'release-y' into develop