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

> On Mar 20, 2020, at 4:59 PM, Peter J. Holzer <hjp-pgsql@hjp.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
> 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

OP  has said small gaps are ok. To me that says the requirement is capricious but we haven’t heard the rationale for
therequirement yet (or I missed it) 

Aside: apologies for the empty message earlier