Horton

Re: POC: Sharing record typmods between backends

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Dilip Kumar <dilipbalaut@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-08-13T02:52:57Z
Lists: pgsql-hackers 
On Fri, Aug 11, 2017 at 9:55 PM, Andres Freund <andres@anarazel.de> wrote:
> Well, most of the potential usecases for dsmhash I've heard about so
> far, don't actually benefit much from incremental growth. In nearly all
> the implementations I've seen incremental move ends up requiring more
> total cycles than doing it at once, and for parallelism type usecases
> the stall isn't really an issue.  So yes, I think this is something
> worth considering.   If we were to actually use DHT for shared caches or
> such, this'd be different, but that seems darned far off.

I think it'd be pretty interesting to look at replacing parts of the
stats collector machinery with something DHT-based.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Remove TupleDesc remapping logic from tqueue.c.

  2. Add support for coordinating record typmods among parallel workers.

  3. Improve division of labor between execParallel.c and nodeGather[Merge].c.

  4. Add minimal regression test for blessed record type transfer.

  5. Consolidate the function pointer types used by dshash.c.

  6. Fix unlikely shared memory leak after failure in dshash_create().

  7. Refactor typcache.c's record typmod hash table.

  8. Add a hash_combine function for mixing hash values.

  9. Backpatch introduction of TupleDescAttr(tupdesc, i).

  10. Partially flatten struct tupleDesc so that it can be used in DSM.

  11. Change tupledesc->attrs[n] to TupleDescAttr(tupledesc, n).