Horton

Re: Add bump memory context type and use it for tuplesorts

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, David Rowley <dgrowleyml@gmail.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2024-02-17T01:10:48Z
Lists: pgsql-hackers 
Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> On 2/17/24 00:14, Tom Lane wrote:
>> The conclusion was that the specific invalid values didn't matter as
>> much on the other platforms as they do with glibc.  But right now you
>> have a fifty-fifty chance that a pointer to garbage will look valid.
>> Do we want to increase those odds?

> Not sure. The ability to detect bogus pointers seems valuable, but is
> the difference between 4/8 and 3/8 really qualitatively different? If it
> is, maybe we should try to increase it by simply adding a bit.

I think it'd be worth taking a fresh look at the bit allocation in the
header word to see if we can squeeze another bit without too much
pain.  There's basically no remaining headroom in the current design,
and it starts to seem like we want some.  (I'm also wondering whether
the palloc_aligned stuff should have been done some other way than
by consuming a context type ID.)

			regards, tom lane

Commits

  1. Update mmgr's README to mention BumpContext

  2. Push dedicated BumpBlocks to the tail of the blocks list

  3. Improve test coverage in bump.c

  4. Fix incorrect KeeperBlock macro in bump.c

  5. Use bump memory context for tuplesorts

  6. Introduce a bump memory allocator

  7. Enlarge bit-space for MemoryContextMethodID