Vihang Karajgaonkar created HIVE-21596:
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Summary: HiveMetastoreClient should be able to connect to older
metastore servers
Key: HIVE-21596
URL: https://issues.apache.org/jira/browse/HIVE-21596
Project: Hive
Issue Type: Improvement
Reporter: Vihang Karajgaonkar
Assignee: Vihang Karajgaonkar
{{HiveMetastoreClient}} currently depends on the fact that both the client and
server versions are the same. Additionally, since the server APIs are backwards
compatible, it is possible for a older client (eg. 2.1.0 client version) to
connect to a newer server (eg. 3.1.0 server version) without any issues. This
is useful in setups where HMS is deployed in a remote mode and clients connect
to it remotely.
It would be a good improvement if a newer version {{HiveMetastoreClient }} can
connect to the a newer server version. When a newer client is talking to a
older server following things can happen:
1. Client invokes a RPC to the older server which doesn't exist.
In such a case, thrift will throw {{Invalid method name}} exception which
should be automatically be handled by the clients since each API throws
TException.
2. Client invokes a RPC using thrift objects which has new fields added.
When a new field is added to a thrift object, the server does not deserialize
the field in the first place since it does not know about that field id. So the
wire-compatibility exists already. However, the client side application should
understand the implications of such a behavior. In such cases, it would be
better for the client to throw exception by checking the server version which
was added in HIVE-21484
3. If the newer client has re-implemented a certain API, for example, using
newer thrift API the client will start seeing exception {{Invalid method name}}
This can be handled on the client side by making sure that the newer
implementation is conditional to the server version. Which means client should
check the server version and invoke the new implementation only if the server
version supports the newer API. (On a side note, it would be great if metastore
also gives information of which APIs are supported for a given version)
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