| From: | Peter Eisentraut <peter(at)eisentraut(dot)org> |
|---|---|
| To: | Aleksander Alekseev <aleksander(at)timescale(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Cc: | Maxim Orlov <orlovmg(at)gmail(dot)com>, Shubham Khanna <khannashubham1197(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Chris Travers <chris(at)orioledata(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Chris Travers <chris(dot)travers(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Fedor Sigaev <teodor(at)sigaev(dot)ru>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Konstantin Knizhnik <knizhnik(at)garret(dot)ru>, Nikita Glukhov <n(dot)gluhov(at)postgrespro(dot)ru>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru> |
| Subject: | Re: Add 64-bit XIDs into PostgreSQL 15 |
| Date: | 2024-07-25 10:19:39 |
| Message-ID: | 76c9eaf2-a924-4df1-8cdc-c6be7d5cf7ac@eisentraut.org |
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| Lists: | pgsql-hackers |
On 23.07.24 11:13, Aleksander Alekseev wrote:
>> Here is the fix. It can be tested like this:
>> [...]
>
> PFA the rebased patchset.
I'm wondering about the 64-bit GUCs.
At first, it makes sense that if there are settings that are counted in
terms of transactions, and transaction numbers are 64-bit integers, then
those settings should accept 64-bit integers.
But what is the purpose and effect of setting those parameters to such
huge numbers? For example, what is the usability of being able to set
vacuum_failsafe_age = 500000000000
I think in the world of 32-bit transaction IDs, you can intuitively
interpret most of these "transaction age" settings as "percent toward
disaster". For example,
vacuum_freeze_table_age = 150000000
is 7% toward disaster, and
vacuum_failsafe_age = 1600000000
is 75% toward disaster.
However, if there is no more disaster threshold at 2^31, what is the
guidance for setting these? Or more radically, why even run
transaction-count-based vacuum at all?
Conversely, if there is still some threshold (not disaster, but
efficiency or something else), would it still be useful to keep these
settings well below 2^31? In which case, we might not need 64-bit GUCs.
Your 0004 patch adds support for 64-bit GUCs but doesn't actually
convert any existing GUCs to use that. (Unlike the reloptions, which
your patch coverts.) And so there is no documentation about these
questions.
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