@SequenceGenerator generating wrong sequence numbers on an Oracle database

Hello,
I have a JPA entity with the following annotation:
@SequenceGenerator(name = "PERS_GEN", sequenceName = "PERS_SEQ", initialValue = 1, allocationSize = 1)
But the ids created by this sequence are not incrementing one by one;they increment 20 by 20. What is the cause of this?And how can it be sold?

Hello,
You will need to reference the database docs on what the database cache setting means or how it behaves, or post on the JDBC forums as I don't really know. My testing by calling SELECT seq.NEXTVAL FROM dual repeatedly caused it to return numbers sequentially based on the increment by value. I suspect this was because I was using the same session/connect etc and might be different if using different connections, timing etc. Have you tried creating the sequence with the nocache option? The cache 20 is not something that would be set by EclipseLink and is likely a database default, and I do not see why START WITH 21 would be used if the annotation specified initialValue = 1 - how are you checking the sequence that gets created? You can turn on EclipseLink logging to Finest to see the SQL it generates, but I would suggest you create the sequence object yourself - or have JPA create a DDL file and use it to create the tables. See http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_(ELUG)#Using_EclipseLink_JPA_Extensions_for_Schema_Generation for ddl generation options.
I found this http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:369390500346406705 discussion on database sequence cache sizes that might help.
Regards,
Chris

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wayneb wrote:
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maybe some user prepared a new record. Then went to some new years eve party and when he came back at the begining of next year he commited the data (record send to database, database is adding date column by some trigger...).
>
The sequence is created by "CREATE SEQUENCE MESSAGE_NUMBER START WITH 10000000 INCREMENT BY 1 MINVALUE 10000000 CACHE 20 NOCYCLE NOORDER"
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>
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I seek some advice from anyone with first hand experience in this area.
My need is simple; generate a new ID number for every order for use as the primary key.
Obviously this simple exercise could be a bottleneck as volumes ramp up, so I was pleased to find the Oracle feature to generate such numbers (efficiently presumably). However, upon closer reading it was apparent that aborted transactions would result in the loss of the number allocated to to that order if another transaction had obtained the next sequence number already (as one would want it to, rather than serializing transactions).
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CS

user8821725 wrote:
I seek some advice from anyone with first hand experience in this area.
My need is simple; generate a new ID number for every order for use as the primary key.
Obviously this simple exercise could be a bottleneck as volumes ramp up, so I was pleased to find the Oracle feature to generate such numbers (efficiently presumably). However, upon closer reading it was apparent that aborted transactions would result in the loss of the number allocated to to that order if another transaction had obtained the next sequence number already (as one would want it to, rather than serializing transactions).
I don't want to have gaps in the sequence as the system needs a high degree of auditability. One of the very very few reasons for me to have a requirement for "gapless" sequences is if you have a kind of checking mechanism outside of the database that is implemented using this gapless number. I had such a requirement once, when exchanging files with another bank where we had to ensure that each file was transferred correctly and in the right order. Your "high degree of auditability" might be a similiar requirement. Just remember as long as you are still inside the database you can use other mechanisms to increase auditability.
I am thinking of utilising the Autonomous Transaction feature to write the newly acquired sequence number to the order file with a flag indicating that the record is incomplete, and that record is to be skipped by normal system applications (but available to audit reports which will interpret the reason correctly), then returning to the far more extensive main transaction which updates many tables.Hm. I don't see why you want to use Autonomous Transactions for this. It might be useful to lessen locking conflicts , depending how your future sequence mechanism will be built.
>
The other alternative is to control sequence numbers within the application itself, or try to get the sequence number as the very last step before writing the new order record, but this probably won't guarantee gapless reliability either. The ID itself has no significance, and it doesn't matter if an ID was used out of strict date/time sequence, so I really don't want to execute these updates serially.I would go for generating the sequence as the very last step. It needs to be set to NOCACHE of cause. This will garantee that the sequence fetched from mySeq.nextval is gapless. The problem is then in your application. Your application must be built in a way that it ensures to use this sequence, or at least to create a noticable alert when this generated sequence can't be used anymore. In essence this means. Each unhandled (database) error that happens after you fetched the next sequence value must be raised in a way that informs all relevant people about this error.
Example: It might be that you use the sequence to write an order file. What happens if halfway through writing the file your disk runs out of space? This can be such an issue where a sequenced value will be lost. Your organisation must take care of those things.
>
So, my question is this:
a) do most people use the builtin sequence number feature?Yes. But for some tasks a sequence is not the best way, for example if you want a numbering for each item of your order. This "sequence" needs to restart with every new order.
b) if so, is there a standard technique for avoiding or accounting for gaps?NOCACHE => Avoids gaps during generation
Database Trigger => Tries to use the sequence as late as possible
c) if the application must take over this task, should the counter for the last used ID be in a single row table to minimise bottlenecks caused by the thisrecord being locked? There will be several such counters for different aspects of the application, and i thought of having each in its own row in a small table, but I'm concerned about the whole table getting locked and freezing out otherwise-unrelated updates.This is a possibility and the issues you describe are why we avoid such a solution in general. Autonomous transactions help to reduce the locking conflict, but they increase the chance that you produce gaps.
>
Thanks for any advice you may have.
CSOracle can guarantee to produce gapless sequences. But it can't guarantee that your application uses such a sequence in a gapless way.

Generate a sequence

Hi all,
I was wondering if you can help me here.
I am new to Oracle (having come from a SQL Server background) and I need to generate sequence numbers using a function.
This is the scenario
we have a table called APPS_CODES with columns CODE, VALUE
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213, Y
214, Y
215,N
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this is how it needs to be generated:
It needs to select the min(CODE) from the APPS_CODE table where value=Y then concatenate this with the ID from set codes table where DESC=AIR then concatenate this with the sequence. The sequence should be left padded with 0s so as to start from 0000001.
Once the sequence reaches 9999999 then the APPS_CODE table needs to be updated and the current code should now have its value set to N so we can start using the next CODE where value=Y.
So when we reach 21329999999 the next value returned by the fucntion will be 21420000001 uptil 21229999999
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I have created the function which seems to work fine.
However when it gets to the 3 record it fails with the following error message
GEN3
2674040000001
Elapsed: 00:00:00.00
15:59:15 test@CAMDEVF8> /
GEN3
2674040000002
Elapsed: 00:00:00.00
16:03:45 test@CAMDEVF8> /
select gen3 from dual
ERROR at line 1:
ORA-00904: "N3_V": invalid identifier
ORA-06512: at "TUNDE.GEN3", line 15
Any help.
Fucntion is below
Thanks
Create or replace
Function gen3
RETURN VARCHAR2 IS
l_v VARCHAR2(30);
n_v INTEGER;
n2_v VARCHAR2(30);
n3_v NUMBER;
BEGIN
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Al

@SequenceGenerator generating wrong sequence numbers on an Oracle database

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