I filed HBASE-4844 a while ago but never actually provided a patch.
If you can comment on that jira with the exact use case that'd be helpful.
If you wanted to work on a patch that'd be cooler even :)
From: Jan Van Besien <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Sent: Monday, October 29, 2012 2:42 AM
Subject: reading WAL log file from inside coprocessor
I am implementing some functionality as a HBase coprocessor which relies on reading WALEdits from the HBase WAL.
I have to requirements:
- get notified whenever a new WALEdit is written to the WAL
- have access to the actual WAL log file such that I can read from it whenever I want
In a way, this is very similar to how HBase replication works.
The first requirement is easy enough, using the WALObserver coprocessor interface. It is for the second requirement however, that I am asking this question.
HBase replication uses the WALActionsListener interface to get notified when the log files are rolled. There doesn't seem to be a way to do that in a WALObserver (coprocessor interface) though.
I thought of adding a WALActionsListener myself from inside the coprocessor code, but I would need to make sure that it is registered before the preLogRolled method is invoked for the first time.
I also looked at HBASE-4132, but I believe this talks about the WALActionsListener and not the WALObserver.
So.. any hints on how to do WAL reading (like replication) from inside a coprocessor?