Horton

Re: POC: Sharing record typmods between backends

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Thomas Munro <thomas.munro@enterprisedb.com>, Dilip Kumar <dilipbalaut@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-08-13T03:37:27Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Sat, Aug 12, 2017 at 11:30 PM, Andres Freund <andres@anarazel.de> wrote:
>> That seems to involve a lot more than this though, given that currently
>> the stats collector data doesn't entirely have to be in memory. I've
>> seen sites with a lot of databases with quite some per-database stats
>> data. Don't think we can just require that to be in memory :(

> Hmm.  I'm not sure it wouldn't end up being *less* memory.  Don't we
> end up caching 1 copy of it per backend, at least for the database to
> which that backend is connected?  Accessing a shared copy would avoid
> that sort of thing.

Yeah ... the collector itself has got all that in memory anyway.
We do need to think about synchronization issues if we make that
memory globally available, but I find it hard to see how that would
lead to more memory consumption overall than what happens now.

			regards, tom lane

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).