bharathv commented on a change in pull request #1880:
URL: https://github.com/apache/hbase/pull/1880#discussion_r438402629
##########
File path: src/main/asciidoc/_chapters/architecture.adoc
##########
@@ -260,6 +260,73 @@ For region name, we only accept `byte[]` as the parameter
type and it may be a f
Information on non-Java clients and custom protocols is covered in
<<external_apis>>
+[[client.masterregistry]]
+=== Master registry (new as of release 3.0.0)
+
+Client internally works with a _connection registry_ to fetch the metadata
needed by connections.
+This connection registry implementation is responsible for fetching the
following metadata.
+
+* Active master address
+* Current meta region(s) locations
+* Cluster ID (unique to this cluster)
+
+This information is needed as a part of various client operations like
connection set up, scans,
+gets etc. Up until releases 2.x.y, the default connection registry is based on
ZooKeeper as the
+source of truth and the the clients fetched the metadata from zookeeper
znodes. As of release 3.0.0,
+the default implementation for connection registry has been switched to a
master based
+implementation. With this change, the clients now fetch the required metadata
from master RPC end
+points directly. This change was done for the following reasons.
+
+* Reduce load on ZooKeeper since that is critical for cluster operation.
+* Holistic client timeout and retry configurations since the new registry
brings all the client
+operations under HBase rpc framework.
+* Remove the ZooKeeper client dependency on HBase client library.
+
+This means that
+
+* At least a single active or stand by master is needed for cluster connection
setup. Refer to
+<<master.runtime>> for more details.
+* Master can be in a critical path of read/write operations, especially if the
client metadata cache
+is empty or stale.
+* There is higher connection load on the masters that before since the clients
talk directly to
+HMasters instead of ZooKeeper ensemble`
+
+To reduce hot-spotting on a single master, all the masters (active & stand-by)
expose the needed
+service to fetch the connection metadata. This lets the client connect to any
master (not just active).
+
+==== RPC hedging
Review comment:
Not really, the functionality was moved from rpc layer to the master
registry, so from a user perspective it didn't change much. But certain configs
changed, will cover as a part of
https://issues.apache.org/jira/browse/HBASE-24535
##########
File path: src/main/asciidoc/_chapters/architecture.adoc
##########
@@ -260,6 +260,73 @@ For region name, we only accept `byte[]` as the parameter
type and it may be a f
Information on non-Java clients and custom protocols is covered in
<<external_apis>>
+[[client.masterregistry]]
+=== Master registry (new as of release 3.0.0)
Review comment:
Will do as a part of https://issues.apache.org/jira/browse/HBASE-24535.
Thanks for pointing it out.
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