[
https://issues.apache.org/jira/browse/HBASE-7460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13557655#comment-13557655
]
Gary Helmling commented on HBASE-7460:
--------------------------------------
Thanks for taking a look Lars.
bq. Do we still want the RPC engine to be configurable?
I originally added the loadable RPC engines as a way of introducing security
(via SecureRpcEngine) as a completely optional component, so that the existing
WritableRpcEngine could be unchanged. Since we've moved back to a single RPC
engine in trunk, I didn't see any value in keeping the additional complexity of
having it configurable. That capability is only minimally used in tests, which
I was easily able to replace. It's possible there are end user implementations
of RpcEngine, though I kind of doubt it. If there are, maybe it's worth
keeping a configuration based factory. I could do a poll on the user list to
check.
bq. the stopProxy logic can go away, because we're calling close on the RPC
engine?
Yes, that was only doing reference counting on our HBaseClient singleton, so
that we could control when HBaseClient.stop() was called. With an HBaseClient
instance now directly tied to a HConnection instance, we can rely on
HCM.HConnectionImplementation#close() -> ProtobufRpcClientEngine#close() ->
HBaseClient#stop() instead.
> 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.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
