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
