| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com> |
| Cc: | Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: making relfilenodes 56 bits |
| Date: | 2022-06-30 02:42:25 |
| Message-ID: | CA+hUKG+ZrDms7gSjckme8YV2tzxgZ0KVfGcsjaFoKyzQX_f_Mw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Jun 30, 2022 at 12:41 AM Simon Riggs
<simon(dot)riggs(at)enterprisedb(dot)com> wrote:
> The reason to mention this now is that it would give more space than
> 56bit limit being suggested here.
Isn't 2^56 enough, though? Remembering that cluster time runs out
when we've generated 2^64 bytes of WAL, if you want to run out of 56
bit relfile numbers before the end of time you'll need to find a way
to allocate them in less than 2^8 bytes of WAL. That's technically
possible, since SMgr CREATE records are only 42 bytes long, so you
could craft some C code to do nothing but create (and leak)
relfilenodes, but real usage is always accompanied by catalogue
insertions to connect the new relfilenode to a database object,
without which they are utterly useless. So in real life, it takes
many hundreds or typically thousands of bytes, much more than 256.
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