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https://issues.apache.org/jira/browse/HBASE-7460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562356#comment-13562356
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Lars Hofhansl commented on HBASE-7460:
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I do not think we have to keep compatibility in internal classes. We even
change the coprocessor interfaces around. Nobody should call deleteConnection
directly. (Changing the HConnection interface would be a different issue and
should be avoided, but we're not doing that).
On the other hand, maybe for the sake of simplicity and easier review we can
leave the HConnectionManager interface unchanged.
We can definitely change RpcEngine.
(And Re: my comment above about the ticket not being available to waitForProxy,
I now also realize that all the paths that lead to getProxy call
User.getCurrent(), so it's not a problem, we'd just do the same).
> 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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