[HBASE-19134] Make WALKey an Interface; expose Read-Only version to CPs

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.0-beta-1, 2.0.0
• Component/s: Coprocessors, wal
• Hadoop Flags: Reviewed
• Release Note: Made WALKey an Interface and added a WALKeyImpl implementation. WALKey comes through to Coprocessors. WALKey is read-only.
• Assignee: Michael Stack
• Reporter: Michael Stack
• Created: 31/Oct/17 13:00
• Updated: 01/Aug/18 06:20
• Resolved: 08/Dec/17 23:13

Description

WALKey has been made IA.Private in hbase2. Even so, given we don't have an alternative to expose at this time, it is exposed to coprocessors still at a few (now deprecated) locations.

In review of HBASE-18770, Chia-Ping Tsai makes reasonable suggestion that what we expose to CPs be a read-only WALKey. He gets pushback on doing this for hbase2 (Do we even want to expose WALKey to CPs, is WALKey right going forward, etc.). Chia-Ping comes back w/ the below (copied from HBASE-18770):

What we want to fix for WALKey are shown below.

• expose some methods to CP user safety
• refactor/redo

As I see it, adding an interface exposed to CP user for WALKey is a right choice because it can bring some benefit.

• We can expose part of WALKey's methods to CP users - a read-only interface or an interface with some modifiable setting.
• The related CP hooks won't be deprecated
• Doing the refactor for WALKey doesn't essentially impact the CP hook after 2.0 release.

Although, it will be better to redo WALKey before 2.0 release. In short, I think it warrants such an interface.

(We both agree this would be a load of work given WALKey is written to HFiles. Warrants a look though).

Issue Links

• links to: Review Board (master)