RE: Grabbing sequence values blocks in consecutive order: Need a guaranteed method.

Question: Within a single session has anyone ever seen sequence.nextval not return a higher value on subsequent calls (except where the sequence value wrap occurred)?

Now when you have RAC since each instance has its own set of sequence numbers InstanceA could be at 100 while instnanceB could be at 75 so a session connect to B after having been connected to A could return a lower value. If you had an application that connected got a number, disconnected, and then re-connected to get another number in a load balancing environment you could see a lower value. But from within a single session I think you can pretty much count on increasing values.

• Mark D Powell -- Phone (313) 592-5148

-----Original Message-----

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of FmHabash Sent: Tuesday, March 24, 2009 2:45 PM
To: Bobak, Mark; Oracle-L Group
Subject: RE: Grabbing sequence values blocks in consecutive order: Need a guaranteed method.

Thanks Mark.
But how would you do it if the range is unpredictable?

Also ...

It will vary so I can not even predict a range. It may be 2 or 50 values.
It looks though, my options 2e...
1- rely on sequences to get the starting value. 2- have java code increment up to the range determined and insert accordingly .
3- One remaining issue is that for this transaction, I may have multiple java threads doing the work. So I want thread 2 to start incrementing from where thread 1 ended. Am looking for some way I can have thses threads work in sync picking up their starting values.

-----Original Message-----

From: Bobak, Mark <Mark.Bobak_at_proquest.com> Sent: Tuesday, March 24, 2009 1:30 PM
To: fmhabash_at_gmail.com <fmhabash_at_gmail.com>; Oracle-L Group <oracle-l_at_freelists.org>
Subject: RE: Grabbing sequence values blocks in consecutive order: Need a guaranteed method.

So, your app needs to grab a block of sequence values....? How large a block?

One possible solution would be to use a sequence w/ increment by <your sequence block size>. So, if you need a block of 10, create a sequence that is "increment by 10", and then each session will select as follows: Session 1:
Select seq.nextval will get 1
Session 2:
Select seq.nextval will get 11
Session 3:
Select seq.nextval will get 21

Now, in the application logic, it will do 10 inserts, starting with the sequence it fetched. So, session 1 will insert 1-10, 2 will insert 11-20, three will insert 21-30, etc.

You'll have to account how to deal with rollbacks, application crashes, other errors, etc. But, in principle, I think it will work, and still be scalable.

Hope that helps,

-Mark

-----Original Message-----

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of FmHabash Sent: Tuesday, March 24, 2009 1:21 PM
To: Oracle-L Group
Subject: Grabbing sequence values blocks in consecutive order: Need a guaranteed method.

Hi all,
I have a need for a java app to be able in some guaranteed manner to grab a block of sequence values that are consecutive in order. Given the fact that there can potentially be multiple sessions making such request, no session should end up interrupting another's while this sequence values block is being granted.
I know this can be done on java side, but thought may be it can also be done on db as well.
My initial review shows that sequences will never guarantee gapless values. If this is the case, can this still be done at least guaranteeing an ordered (not necessarily consecutive ) values?

Thanks
--

http://www.freelists.org/webpage/oracle-l

--

http://www.freelists.org/webpage/oracle-l

--

http://www.freelists.org/webpage/oracle-l Received on Tue Mar 24 2009 - 13:58:46 CDT