> On Mar 19, 2020, at 4:13 PM, pabloa98 <pabloa98(at)gmail(dot)com> wrote:
>
>
>
> On Thu, Mar 19, 2020 at 2:50 PM Rob Sargent <robjsargent(at)gmail(dot)com <mailto:robjsargent(at)gmail(dot)com>> wrote:
>
>
> > On Mar 19, 2020, at 3:36 PM, pabloa98 <pabloa98(at)gmail(dot)com <mailto:pabloa98(at)gmail(dot)com>> wrote:
> >
> > Hello,
> >
> > My schema requires a counter for each combination of 2 values. Something like:
> >
> > CREATE TABLE counter(
> > group INT NOT NULL,
> > element INT NOT NULL,
> > seq_number INT NOT NULL default 0,
> > CONSTRAINT PRIMARY KEY (group, element)
> > );
> >
> > For each entry in counter, aka for each (group, element) pair, the model requires a seq_number.
> >
> > If I use a table "counter", I could still have counter collisions between 2 transactions. I need truly sequence behavior. Is that possible by using a table like "counter" table, where the counter could be increased out of the transaction so it performs as a sequence without having race conditions between concurrent transactions?
> >
> > The other option is to create sequences for each new pair of (group, element) using triggers. There are millions of pairs. So this approach will generate millions of sequences.
> >
> > How a PostgreSQL database would behave having millions of sequences in a schema? Would it degrade its performance? Is there any negative impact?
> >
> > Regards
> >
> > Pablo
> >
>
> To clarify, are you hoping for consecutive numbers as the each row is added to the table, i.e. “serial”?
>
> What is the intension of “seq_number”?
> >
> >
>
>
> the idea is to have like a serial sequence, but for each pair of (group, element).
>
> so that when we insert rows in another table, we could have something like:
>
>
> group, element, event_id, ...
> 1, 1, 1
> 1, 1, 2
> 1, 1, 3
> 2, 1, 1
> 1, 1, 4
> 1, 3, 1
> 1, 1, 5
> 1, 3, 2
> 2, 1, 2
> 2, 1, 3
>
> The 3rd column is the sequence number we get from the appropriate sequence created by the trigger.
>
> I want to implement a variation of https://stackoverflow.com/a/30204854 <https://stackoverflow.com/a/30204854> and that will generate millions of sequences.
>
>
Then I don’t thing group/element can be a PRIMARY KEY