Horton

Re: POC: Sharing record typmods between backends

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-05-31T16:53:49Z
Lists: pgsql-hackers 
On Wed, May 31, 2017 at 11:16 AM, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> I agree with you. But, if I understand the use case correctly we need
> to store the TupleDesc for the RECORD in shared hash so that it can be
> shared across multiple processes.  I think this can be achieved with
> the simplehash as well.
>
> For getting this done, we need some fixed shared memory for holding
> static members of SH_TYPE and the process which creates the simplehash
> will be responsible for copying these static members to the shared
> location so that other processes can access the SH_TYPE.  And, the
> dynamic part (the actual hash entries) can be allocated using DSA by
> registering SH_ALLOCATE function.

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.

-- 
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).