[jira] [Commented] (HBASE-7460) Cleanup client connection layers

["Gary Helmling (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-7460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13555815#comment-13555815 ] 

Gary Helmling commented on HBASE-7460:
--------------------------------------

Initial patch posted for review: https://reviews.apache.org/r/8979/
                
> Cleanup client connection layers
> --------------------------------
>
>                 Key: HBASE-7460
>                 URL: https://issues.apache.org/jira/browse/HBASE-7460
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client, IPC/RPC
>            Reporter: Gary Helmling
>
> This issue originated from a discussion over in HBASE-7442.  We currently have a broken abstraction with {{HBaseClient}}, where it is bound to a single {{Configuration}} instance at time of construction, but then reused for all connections to all clusters.  This is combined with multiple, overlapping layers of connection caching.
> Going through this code, it seems like we have a lot of mismatch between the higher layers and the lower layers, with too much abstraction in between. At the lower layers, most of the {{ClientCache}} stuff seems completely unused. We currently effectively have an {{HBaseClient}} singleton (for {{SecureClient}} as well in 0.92/0.94) in the client code, as I don't see anything that calls the constructor or {{RpcEngine.getProxy()}} versions with a non-default socket factory. So a lot of the code around this seems like built up waste.
> The fact that a single Configuration is fixed in the {{HBaseClient}} seems like a broken abstraction as it currently stands. In addition to cluster ID, other configuration parameters (max retries, retry sleep) are fixed at time of construction. The more I look at the code, the more it looks like the {{ClientCache}} and sharing the {{HBaseClient}} instance is an unnecessary complication. Why cache the {{HBaseClient}} instances at all? In {{HConnectionManager}}, we already have a mapping from {{Configuration}} to {{HConnection}}. It seems to me like each {{HConnection(Implementation)}} instance should have it's own {{HBaseClient}} instance, doing away with the {{ClientCache}} mapping. This would keep each {{HBaseClient}} associated with a single cluster/configuration and fix the current breakage from reusing the same {{HBaseClient}} against different clusters.
> We need a refactoring of some of the interactions of {{HConnection(Implementation)}}, {{HBaseRPC/RpcEngine}}, and {{HBaseClient}}. Off hand, we might want to expose a separate {{RpcEngine.getClient()}} method that returns a new {{RpcClient}} interface (implemented by {{HBaseClient}}) and move the {{RpcEngine.getProxy()}}/{{stopProxy()}} implementations into the client. So all proxy invocations can go through the same client, without requiring the static client cache. I haven't fully thought this through, so I could be missing other important aspects. But that approach at least seems like a step in the right direction for fixing the client abstractions.

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