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From Apekshit Sharma <a...@cloudera.com>
Subject Re: [DISCUSS] Punt the Coprocessor TableWrapper and CoprocessorHConnection?
Date Wed, 18 Oct 2017 22:12:02 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.

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

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