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

On Mar 19, 2020, at 4:13 PM, pabloa98 <pabloa98@gmail.com> wrote:

On Thu, Mar 19, 2020 at 2:50 PM Rob Sargent <robjsargent@gmail.com> wrote:

> On Mar 19, 2020, at 3:36 PM, pabloa98 <pabloa98@gmail.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 and that will generate millions of sequences.

Then I don’t thing group/element can be a PRIMARY KEY