Date: Tue, 31 Oct 2023 09:10:56 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>, suchithjn22@gmail.com,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: The documentation for storage type 'plain' actually allows
 single byte header
Message-ID: <ZUD84FfPPWv2A-ip@momjian.us>
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On Sat, Oct 21, 2023 at 09:59:04PM -0400, Bruce Momjian wrote:
> On Sat, Oct 21, 2023 at 09:56:13PM -0400, Bruce Momjian wrote:
> > I did some more research.  It turns out that the source slot/planSlot is
> > populating its pg_attribute information via makeTargetEntry() and it
> > has no concept of a storage type.
> > 
> > Digging further, I found that we cannot get rid of the the use of
> > att->attstorage != TYPSTORAGE_PLAIN in macros ATT_IS_PACKABLE and
> > VARLENA_ATT_IS_PACKABLE macros in src/backend/access/common/heaptuple.c
> > because there are internal uses of fill_val() that can't handle packed
> > varlena headers.
> > 
> > I ended up with a doc patch that adds a C comment about this odd
> > behavior and removes doc text about PLAIN storage not using packed
> > headers.
> 
> Oops, patch attached.

Patch applied to all supported versions.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Only you can decide what is important to you.