See HDFS-13150 for full design.
This JIRA is to make the JournalNode-side changes necessary to support serving edits via RPC. This includes interacting with the cache added in HDFS-13607.
[Edit Tail Fast Path Pt 1] Enhance JournalNode with an in-memory cache of recent edit transactions
[Edit Tail Fast Path] Allow SbNN to tail in-progress edits from JN via RPC
[Edit Tail Fast Path Pt 3] NameNode-side changes to support tailing edits via RPC
Journaled Edits Cache is not cleared when formatting the JN