Re: SQL Sequence use cases

[Charles Wilt <charles.wilt@xxxxxxxxx>]

David,

There's a trade off between "sequential-ness" and performance,
particularly with multiple jobs using the same sequence.

If you want a strict sequence between multiple jobs, you have to
specify ORDER and NO CACHE.  But you'll pay a performance price.

If all you really need is a surrogate key shared between tables, then
the defaults of NO ORDER and CACHE 20 provide the best performance.

HTH,
Charles


On Wed, Nov 25, 2009 at 2:07 PM, David Gibbs <david@xxxxxxxxxxxx> wrote:
> Folks:
>
> I'm having a bit of a struggle understanding the SQL Sequence business cases.
>
> I understand the conceptual idea behind SQL Sequences ... but the behavior I'm observing in testing is kind of baffling me.
>
> In interactive SQL (no commitment control), I created a SQL sequence in a schema starting at 1 with a cache value of 10.
>
> I then run the following statement:
> select (next value for TESTSEQ1) from sysibm/sysdummy1
>
> I get a result of '1'.
>
> If I run the same SQL statement again, I get the result '2'.
>
> However, if I start interactive SQL in another job, and run the same statement I get a value of '11'.
>
>  From what I understand about SQL Sequences, you're supposed to use it to get a sequential number from SQL on an select, insert, or update statement.
>
> What I'm not understanding is why the 'sequential' number isn't so sequential ... and very gappy.
>
> I do know that I could use the no cache option to disable caching ... but I'm just trying to understand the business cases for the sequence concept.
>
> Thanks!
>
> david
>
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