Re: Zstandard support for toast compression

Hi,

> Yeah - I think we had better reserve the fourth bit pattern for
> something extensible e.g. another byte or several to specify the
> actual method, so that we don't have a hard limit of 4 methods.

TWIMC there is an ongoing discussion [1] of making TOAST pointers
extendable since this is a dependency for several patches that are
currently in development.

TL;DR the consensus so far seems to be using varattrib_1b_e.va_tag as
a sign of an alternative / extended TOAST pointer content. For the
on-disk values va_tag currently stores a constant 18 (VARTAG_ONDISK).
Where 18 is sizeof(varatt_external) + /* header size */ 2, which seems
to be not extremely useful anyway. If you are interested in the topic
please consider joining the thread.

[1]: https://postgr.es/m/CAN-LCVMq2X%3Dfhx7KLxfeDyb3P%2BBXuCkHC0g%3D9GF%2BJD4izfVa0Q%40mail.gmail.com

-- 
Best regards,
Aleksander Alekseev