Date: Tue, 7 Sep 2021 17:55:54 +0200
From: Christoph Berg <myon@debian.org>
To: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: VARDATA_COMPRESSED_GET_COMPRESS_METHOD comment?
Message-ID: <YTeLipdnSOg4NNcI@msg.df7cb.de>
Mail-Followup-To: Christoph Berg <myon@debian.org>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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In postgres.h, there are these macros for working with compressed
toast:

                                                  vvvvvvvv
/* Decompressed size and compression method of an external compressed Datum */
#define VARDATA_COMPRESSED_GET_EXTSIZE(PTR) \
    (((varattrib_4b *) (PTR))->va_compressed.va_tcinfo & VARLENA_EXTSIZE_MASK)
#define VARDATA_COMPRESSED_GET_COMPRESS_METHOD(PTR) \
    (((varattrib_4b *) (PTR))->va_compressed.va_tcinfo >> VARLENA_EXTSIZE_BITS)

/* Same, when working directly with a struct varatt_external */
#define VARATT_EXTERNAL_GET_EXTSIZE(toast_pointer) \
    ((toast_pointer).va_extinfo & VARLENA_EXTSIZE_MASK)
#define VARATT_EXTERNAL_GET_COMPRESS_METHOD(toast_pointer) \
    ((toast_pointer).va_extinfo >> VARLENA_EXTSIZE_BITS)


On the first line, is the comment "external" correct? It took me quite
a while to realize that the first two macros are the methods to be
used on an *inline* compressed Datum, when the second set is used for
varlenas in toast tables.

Context: Me figuring out https://github.com/credativ/toastinfo/blob/master/toastinfo.c#L119-L128

Christoph