Horton

Re: POC: Sharing record typmods between backends

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-05-31T17:46:36Z
Lists: pgsql-hackers 
On 2017-05-31 13:27:28 -0400, Dilip Kumar wrote:
> On Wed, May 31, 2017 at 12:53 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> > Well, SH_TYPE's members SH_ELEMENT_TYPE *data and void *private_data
> > are not going to work in DSM, because they are pointers.  You can
> > doubtless come up with a way around that problem, but I guess the
> > question is whether that's actually any better than just using DHT.
> 
> Probably I misunderstood the question. I assumed that we need to bring
> in DHT only for achieving this goal. But, if the question is simply
> the comparison of DHT vs simplehash for this particular case then I
> agree that DHT is a more appropriate choice.

Yea, I don't think simplehash is the best choice here.  It's worthwhile
to use it for performance critical bits, but using it for everything
would just increase code size without much benefit.  I'd tentatively
assume that anonymous record type aren't going to be super common, and
that this is going to be the biggest bottleneck if you use them.

- Andres

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).