[HBASE-10940] [0.89-fb] Rebalance primaries in-non disruptive way

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.89-fb
• Fix Version/s: 0.89-fb
• Component/s: Region Assignment
• Assignee: Adela Maznikar
• Reporter: Adela Maznikar
• Created: 09/Apr/14 00:26
• Updated: 17/Jun/22 05:30
• Resolved: 09/Apr/14 00:30

Description

Added an option RegionPlacement -bp (balance primaries).
Sometimes in production we hit a case where some of the regionservers are serving less number of regions than the rest and just updating the assignment plan doesn't help since locality is highest on those locations and locality is the highest parameter considered when we produce assignment plan for primaries.

We want to switch primary and tertiary in a case where the regionserver has
more than average primaries and more primaries assigned than the
regionserver where teritary is (and tertiary has less than average). We do
bfs traversal from each node (node being a regionserver, and there is an edge from machine serving primary to machine serving tertiary for a particular region) until we find the node to which there is a
path and that node has less primaries assigned. Then we switch primary and
tertiary for all nodes on the path. We do that for each node. (node ==
machine).

The motivation of the approach is - we want to move the region to a location where locality is high enough.