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https://issues.apache.org/jira/browse/HBASE-7460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562041#comment-13562041
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Lars Hofhansl commented on HBASE-7460:
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Hey [~ghelmling], are you still planning on making a 0.94 port?
> 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
> Assignee: Gary Helmling
> Fix For: 0.96.0
>
> Attachments: HBASE-7460_2.patch
>
>
> 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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