Horton

Re: making relfilenodes 56 bits

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

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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
To: Simon Riggs <simon.riggs@enterprisedb.com>
Cc: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Thomas Munro <thomas.munro@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-06-28T18:18:46Z
Lists: pgsql-hackers 
On Tue, 28 Jun 2022 at 13:45, Simon Riggs <simon.riggs@enterprisedb.com> wrote:
> but since the number of combinations is usually 1, but even then, low,
> it can be cached easily in a smgr array and included in the checkpoint
> record (or nearby) for ease of use.

I was reading the thread to keep up with storage-related prototypes
and patches, and this specifically doesn't sound quite right to me. I
do not know what values you considered to be 'low' or what 'can be
cached easily', so here's some field data:

I have seen PostgreSQL clusters that utilized the relative isolation
of seperate databases within the same cluster (instance / postmaster)
to provide higher guarantees of data access isolation while still
being able to share a resource pool, which resulted in several
clusters containing upwards of 100 databases.

I will be the first to admit that it is quite unlikely to be common
practise, but this workload increases the number of dbOid+spcOid
combinations to 100s (even while using only a single tablespace),
which in my opinion requires some more thought than just handwaving it
into an smgr array and/or checkpoint records.


Kind regards,

Matthias van de Meent

Commits

  1. Fix typos in comments, code and documentation

  2. Increase width of RelFileNumbers from 32 bits to 56 bits.

  3. Move RelFileNumber declarations to common/relpath.h.

  4. Include RelFileLocator fields individually in BufferTag.

  5. Convert macros to static inline functions (buf_internals.h)

  6. Remove the restriction that the relmap must be 512 bytes.

  7. Change internal RelFileNode references to RelFileNumber or RelFileLocator.

  8. Reorder subskiplsn in pg_subscription to avoid alignment issues.

  9. Fix DROP {DATABASE,TABLESPACE} on Windows.

  10. Restructure smgr API as per recent proposal. smgr no longer depends on