HBASE-5699 we introduced multiple wal, and after some succeeding works we now have two main kinds of wal providers: DefaultWALProvider and RegionGroupingProvider, while DefaultWALProvider supplies a single wal per regionserver, RegionGroupingProvider supplies multiple wals according to the RegionGroupingStrategy it's using.
Now there're two kinds of RegionGroupingStrategy: identity and bounded, in which "identity" only for testing (trial) purpose and "bounded" for randomly assigning region writes to bounded number of wals. Although the "bounded" strategy is good enough for IO leverage, we may still want a more "designed" way to distribute the region writes, like having one wal group per business.
Since we already have namespace for multi-tenancy, it would be good to have namespace-based grouping strategy, and this is exactly what this JIRA is for.
There might be more benefits if we have namespace-based wal group, like only replicating data for the namespace in need w/o filtering anything useless, or only force region flush for the heavy loaded namespace, etc. although we won't include all these in this single JIRA.