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https://issues.apache.org/jira/browse/IMPALA-9370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17108626#comment-17108626
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Sahil Takiar commented on IMPALA-9370:
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Some other follow ups from IMPALA-9199:
There is a circular dependency between QueryDriver, ClientRequestState, and
Coordinator - e.g. the Coordinator contains the member variables
{{parent_driver_}} and {{parent_request_state_}} it would be ideal if we
removed these circular dependencies
> Re-factor ImpalaServer, ClientRequestState, Coordinator protocol
> ----------------------------------------------------------------
>
> Key: IMPALA-9370
> URL: https://issues.apache.org/jira/browse/IMPALA-9370
> Project: IMPALA
> Issue Type: Sub-task
> Components: Backend
> Reporter: Sahil Takiar
> Assignee: Sahil Takiar
> Priority: Major
>
> All of these classes need to be updated to support transparent query retries,
> and each one could due with some re-factoring so that query retries don't
> make this code even more complex. For now, I'm going to list out some ideas /
> suggestions:
> * Rename ImpalaServer to ImpalaService, I think ImpalaServer is a bit of a
> misnomer because Impala isn't implementing its own server (it uses Thrift for
> that) instead it is providing a "service" to end users - this name is
> consistent with Thrift "service"s as well
> * Split up ClientRequestState - I'm not sure I fully understand what
> ClientRequestState is suppose to encapsulate - perhaps originally it captured
> the state of the actual client request as well as some helper code, but it
> seems to have evolved over time; it doesn't really look like a purely
> "stateful" object any more (e.g. it manages admission control submission)
> One possible end state could be:
> ImpalaService <–> QueryDriver (has a ClientRequestState that is not exposed
> externally) <–> QueryInstance <–> Coordinator
> The QueryDriver is responsible for E2E execution of a query, including all
> stages such as parsing / planning of a query, submission to admission
> control, and backend execution. A QueryInstance is a single instance of a
> query, this is necessary for query retry support since a single query can be
> run multiple times. The Coordinator remains mostly the same - it is purely
> responsible for *backend* coordination / execution of a query.
> This provides an opportunity to move a lot of the execution specific logic
> out of ImpalaServer and into QueryDriver. Currently, ImpalaServer is
> responsible for submitting the query to the fe/ and then passing the result
> to the ClientRequestState which submits it for admission control (and
> eventually the Coordinator for execution).
> QueryDriver encapsulates the E2E execution of a query (starting from a query
> string, and then returning the results of a query) (inspired by Hive's
> IDriver interface -
> [https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/IDriver.java]).
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