Horton

Re: Reducing the chunk header sizes on all memory context types

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Julien Rouhaud <rjuju123@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-10-03T19:37:50Z
Lists: pgsql-hackers 
David Rowley <dgrowleyml@gmail.com> writes:
> Andres did mention to me off-list about perhaps adding a boolean field
> to FunctionCallInfoBaseData to indicate if the return value can be
> assumed to be in CurrentMemoryContext.  I feel like that might be
> quite a bit of work to go and change all functions to ensure that
> that's properly populated.

That seems like the right basic answer, but wrong in detail.  We have only
a tiny number of places that care about this --- aggregates and window
functions basically --- and those already have a bunch of special calling
conventions.  So changing the generic fmgr APIs has side-effects far
beyond what's justified.

I think what we should look at is extending the aggregate/window
function APIs so that such functions can report where they put their
output, and then we can nuke MemoryContextContains(), with the
code code set up to assume that it has to copy if the called function
didn't report anything.  The existing FunctionCallInfo.resultinfo
mechanism (cf. ReturnSetInfo for SRFs) is probably the right thing
to pass the flag through.

I can take a look at this once the release dust settles a little.

			regards, tom lane

Commits

  1. Harden memory context allocators against bogus chunk pointers.

  2. Improve our ability to detect bogus pointers passed to pfree et al.

  3. Remove MemoryContextContains().

  4. Remove uses of MemoryContextContains in nodeAgg.c and nodeWindowAgg.c.

  5. Temporarily make MemoryContextContains return false

  6. Make MemoryContextContains work correctly again

  7. Make more effort to put a sentinel at the end of allocated memory

  8. Fix some possibly latent bugs in slab.c

  9. Various cleanups of the new memory context header code

  10. Revert "Add missing padding from MemoryChunk struct"

  11. Use MAXALIGN() in calculations using sizeof(SlabBlock)

  12. Add missing padding from MemoryChunk struct

  13. Improve performance of and reduce overheads of memory management