Re: Could postgres12 support millions of sequences? (like 10 million)

On Fri, Mar 20, 2020 at 3:59 PM Peter J. Holzer <hjp-pgsql(at)hjp(dot)at> wrote:

> On 2020-03-19 16:48:19 -0700, David G. Johnston wrote:
> > First, it sounds like you care about there being no gaps in the records
> you end
> > up saving. If that is the case then sequences will not work for you.
>
> I think (but I would love to be proven wrong), that *nothing* will work
> reliably, if
>
> 1) you need gapless numbers which are strictly allocated in sequence
>
A little gap is acceptable. We cannot afford a 100 gap though.

2) you have transactions
> 3) you don't want to block
>
> Rationale:
>
> Regardless of how you get the next number, the following scenario is
> always possible:
>
> Session1: get next number
> Session2: get next nummber
> Session1: rollback
> Session2: commit
>
> At this point you have a gap.
>
> If you can afford to block, I think a simple approach like
>
> create table s(id int, counter int);
> ...
> begin;
> ...
> update s set counter = counter + 1 where id = $whatever returning
> counter;
> -- use counter
> commit;
>
> should work. But that effectively serializes your transactions and may
> cause some to be aborted to prevent deadlocks.
>
> hp
>
> --
> _ | Peter J. Holzer | Story must make more sense than reality.
> |_|_) | |
> | | | hjp(at)hjp(dot)at | -- Charles Stross, "Creative writing
> __/ | http://www.hjp.at/ | challenge!"
>