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https://issues.apache.org/jira/browse/HBASE-7460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13541037#comment-13541037
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Gary Helmling commented on HBASE-7460:
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[[email protected]] Yes, it would be good to sync up in this area and align
our plans. If going through with exposing the protobuf Service implementations
proves out, dropping the dynamic proxying would definitely simplify some
things, and I also got the impression that there was a lot of accumulated cruft
to weed out, ClientCache being a prime example.
Let's streamline the intermediate code first, then look at cutting out the wire
transfer overhead. Benoit's docs make good reading. There are a lot of gains
to be made there as well.
> 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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