[jira] [Assigned] (HIVE-21596) HiveMetastoreClient should be able to connect to older metastore servers

["Vihang Karajgaonkar (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-21596?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vihang Karajgaonkar reassigned HIVE-21596:
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> 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
>            Priority: Major
>
> {{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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