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https://issues.apache.org/jira/browse/HBASE-7460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562276#comment-13562276
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Gary Helmling commented on HBASE-7460:
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bq. One thing I found I had to do was to have WritableRpcEngine and
SecureRpcEngine implement Configurable and then initialize the HBaseClient in
the setConf(...) method.
Thanks for the reminder. I had started down a similar path in the trunk
version, but abandoned that when I saw I could do direct instantiation instead.
For 0.94 where we need to preserve the RpcEngine factory aspect, we'll
definitely need this.
One issue I'm running in to is to what extent do we want to do incompatible
changes within RpcEngine. There we have:
{code:java}
VersionedProtocol getProxy(Class<? extends VersionedProtocol> protocol,
long clientVersion, InetSocketAddress addr,
User ticket, Configuration conf,
SocketFactory factory, int rpcTimeout) throws IOException;
{code}
The approach I'm planning would change this like trunk to eliminate some unused
parameters. This would impact anyone who had implemented their own RpcEngine,
but this seems like a semi-internal internal, so modifying it seemed reasonable
to me.
The trunk patch also has some changes to HConnectionManager method signatures
(dropping the unneeded stopProxy param from deleteConnection\*). Should the
HConnectionManager interface changes be avoided in 0.94? We could keep the
existing signatures, but just ignore the stopProxy parameter. Breaking this
interface for clients seems like it would cause a lot more problems.
> 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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