| From: | Aleksander Alekseev <aleksander(at)timescale(dot)com> |
|---|---|
| To: | pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Cc: | Nikolay Shaplov <dhyan(at)nataraj(dot)su>, Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net> |
| Subject: | Re: Zstandard support for toast compression |
| Date: | 2023-05-23 14:56:13 |
| Message-ID: | CAJ7c6TP+3JRnadTzCAvSMxjV5zi6Wndc36kiZf6xiCDsmbbpsA@mail.gmail.com |
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| Lists: | pgsql-hackers |
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
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