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From Andrew Purtell <apurt...@apache.org>
Subject Re: [DISCUSS] Punt the Coprocessor TableWrapper and CoprocessorHConnection?
Date Wed, 18 Oct 2017 22:29:33 GMT
> I remember Andrew saying same thing about CoprocessorEnvironment#getTable
functions during the review of HBASE-17732, that we should get rid of them
and let CP do their own table resource management like all other things.

Yes

> The above 'trick' is now commonplace in servers as the Master and RegionServer
always make Connections that will short-circuit if an opportunity

No need for CoprocessorHConnection, then.



On Wed, Oct 18, 2017 at 3:12 PM, Apekshit Sharma <appy@cloudera.com> wrote:

> +1
> I remember Andrew saying same thing about CoprocessorEnvironment#getTable
> functions during the review of HBASE-17732, that we should get rid of them
> and let CP do their own table resource management like all other things.
>
> On Wed, Oct 18, 2017 at 2:45 PM, Stack <stack@duboce.net> wrote:
>
> > tl;dr I believe the original intent for TableWrapper and
> > CoprocessorHConnection can now be gotten elsewhere so we should purge
> these
> > classes.
> >
> > In base CoprocessorEnvironment, there are methods to return a Table
> > instance. There are none to return an Admin. In our code base, the only
> > user is the AccessController. Phoenix uses it twice in its Indexer
> > implementation.
> >
> > When you call CE#getTable, the default implementation in
> > BaseEnvironemnt calls HTableWrapper.createWrapper which takes a
> > BaseEnvironment List in which we keep all Table instances. On shutdown of
> > the coprocessor, the list is iterated and all tables are closed.
> >
> > Going via TableWrapper, the class comment says:
> >
> > * A wrapper for HTable. Can be used to restrict privilege.
> > *
> > * Currently it just helps to track tables opened by a Coprocessor and
> > * facilitate close of them if it is aborted.
> > *
> > * We also disallow row locking.
> > *
> > * There is nothing now that will stop a coprocessor from using HTable
> > * objects directly instead of this API, but in the future we intend to
> > * analyze coprocessor implementations as they are loaded and reject those
> > * which attempt to use objects and methods outside the Environment
> > * sandbox.
> >
> >
> > TableWrapper by my reading delegates all calls to a Table instance with
> no
> > interception (there is not rowlocking to override anymore). On open, we
> do
> > ensure the Table is up on a CoprocessorHConnection which does the
> > following:
> >
> > * Connection to an HTable from within a Coprocessor. We can do some
> > nice tricks since we know we
> > * are on a regionserver, for instance skipping the full
> > serialization/deserialization of objects
> > * when talking to the server.
> >
> >
> > The above 'trick' is now commonplace in servers as the Master and
> > RegionServer always make Connections that will short-circuit if an
> > opportunity.
> >
> > As I read TableWrapper and CoprocessorHConnection, they were written at
> > another time when Table construction was heavyweight and Table#close was
> > not expected of clients and before the introduction of the general
> > Server-side short-circuit Connection facility.
> >
> > Unless objection, I think we should purge them.
> >
> > Writing here in case I'm missing some key facility they provide.
> >
> > Thanks,
> > St.Ack
> >
>
>
>
> --
>
> -- Appy
>



-- 
Best regards,
Andrew

Words like orphans lost among the crosstalk, meaning torn from truth's
decrepit hands
   - A23, Crosstalk

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