Drop ROOT and instead store META location(s) directly in ZooKeeper
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Key: HBASE-3171
URL: https://issues.apache.org/jira/browse/HBASE-3171
Project: HBase
Issue Type: Improvement
Components: client, master, regionserver, zookeeper
Reporter: Jonathan Gray
Fix For: 0.92.0
Rather than storing the ROOT region location in ZooKeeper, going to ROOT, and
reading the META location, we should just store the META location directly in
ZooKeeper.
The purpose of the root region from the bigtable paper was to support multiple
meta regions. Currently, we explicitly only support a single meta region, so
the translation from our current code of a single root location to a single
meta location will be very simple. Long-term, it seems reasonable that we
could store several meta region locations in ZK. There's been some discussion
in HBASE-1755 about actually moving META into ZK, but I think this jira is a
good step towards taking some of the complexity out of how we have to deal with
catalog tables everywhere.
As-is, a new client already requires ZK to get the root location, so this would
not change those requirements in any way.
The primary motivation for this is to simplify things like CatalogTracker. The
way we can handle root in that class is really simple but the tracking of meta
is difficulty and a bit hacky. This hack on tracking of the meta location is
what caused one of the bugs over in HBASE-3159.
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