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: 2017-08-16T12:42:27Z
Lists: pgsql-hackers 
On Tue, Aug 15, 2017 at 8:34 PM, Andres Freund <andres@anarazel.de> wrote:
> On 2017-08-15 20:30:16 -0400, Robert Haas wrote:
>> On Tue, Aug 15, 2017 at 6:06 PM, Andres Freund <andres@anarazel.de> wrote:
>> > Interesting. I was apparently thinking slightly differently. I'd have
>> > thought we'd have Session struct in statically allocated shared
>> > memory. Which'd then have dsa_handle, dshash_table_handle, ... members.
>>
>> Sounds an awful lot like what we're already doing with PGPROC.
>
> Except it'd be shared between leader and workers. So no, not really.

There's precedent for using it that way, though - cf. group locking.
And in practice you're going to need an array of the same length as
the procarray.  It's maybe not quite the same thing, but it smells
pretty similar.

-- 
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).