Horton

Re: Non-replayable WAL records through overflows and >MaxAllocSize lengths

Matthias van de Meent <boekewurm+postgres@gmail.com>

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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2022-07-15T09:25:54Z
Lists: pgsql-hackers 
On Mon, 14 Mar 2022 at 18:14, Andres Freund <andres@anarazel.de> wrote:
>
> A random thought I had while thinking about the size limits: We could use the
> low bits of the length and xl_prev to store XLR_SPECIAL_REL_UPDATE |
> XLR_CHECK_CONSISTENCY and give rmgrs the full 8 bit of xl_info. Which would
> allow us to e.g. get away from needing Heap2. Which would aestethically be
> pleasing.

I just remembered your comment while going through the xlog code and
thought this about the same issue: We still have 2 bytes of padding in
XLogRecord, between xl_rmid and xl_crc. Can't we instead use that
space for rmgr-specific flags, as opposed to stealing bits from
xl_info?


Kind regards,

Matthias van de Meent

Commits

  1. Add more protections in WAL record APIs against overflows

  2. Add overflow protection for block-related data in WAL records

  3. Change internal RelFileNode references to RelFileNumber or RelFileLocator.

  4. Revamp the WAL record format.