Horton

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

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Julien Rouhaud <rjuju123@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-09-07T21:32:10Z
Lists: pgsql-hackers 
On Thu, 8 Sept 2022 at 03:08, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 4. For aset.c, I'd be inclined to have it compute the AllocBlock
> address implied by the putative chunk header, and then run through
> the context's alloc blocks and see if any of them match.  If we
> do find a match, and the chunk address is within the allocated
> length of the block, call it good.  Probably the same could be done
> for the other two methods.
>
> Step 4 is annoyingly expensive, but perhaps not too awful given
> the way we step up alloc block sizes.  We should make sure that
> any context we want to use MemoryContextContains with is allowed
> to let its blocks grow large, so that there can't be too many
> of them.

Thanks for the idea. I've not come up with anything better other than
remove the calls to MemoryContextContains and just copy the Datum each
time.  That doesn't fix the problems with function, however.

I'll go code up your idea and see if doing that triggers any other ideas.

David

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