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

On 3/19/20 7:38 PM, Michael Lewis wrote:
>
>
> On Thu, Mar 19, 2020, 5:48 PM David G. Johnston
> <david.g.johnston@gmail.com <mailto:david.g.johnston@gmail.com>> wrote:
>
>     However, one other consideration with sequences: do you care that
>     PostgreSQL will cache/pin (i.e., no release) every single sequence
>     you touch for the lifetime of the session? (I do not think DISCARD
>     matters here but I'm just guessing)
>
>
>
> Would you expand on this point or is there someplace specific in the
> documentation on this?
>

See the section starting here:

https://www.postgresql.org/docs/12/sql-createsequence.html

Notes

"Unexpected results might be obtained if a cache setting greater than
one is used for a sequence object that will be used concurrently by
multiple sessions. Each session will allocate and cache successive
sequence values during one access to the sequence object and increase
the sequence object's last_value accordingly. Then, the next cache-1
uses of nextval within that session simply return the preallocated
values without touching the sequence object. So, any numbers allocated
but not used within a session will be lost when that session ends,
resulting in “holes” in the sequence.

...
"

--
Adrian Klaver
adrian.klaver@aklaver.com