Wrong sequencing with Oracle db using sequence table?

Question

Hi,
we have a strange problem resulting in primary key violations in a table which is using a sequence (no native sequencing, but a sequence table).
We use Oracle 9.2.0.x
We have a table which is mapped to a Java type which has two derived types, i. e. in the table, two different "object types" are contained (the table contains all attributes of both classes). This table uses a sequence key as primary key.
This works pretty fine when the table is left empty in the beginning.
However, if we fill 15 records in this table by a SQL script - not by toplink! - (for migration purposes), and then set the initial sequence value in the sequence table to 500 (which should be greater than 15 ;-) by the same SQL script, then restart the application server (Bea Weblogic), and then try to add new records via Toplink, we get a primary key violation.
It sounds odd but it seems as if Toplink would store the initial sequence value somewhere else and does not care about the value we entered "manually" in the sequence table.
Can anybody give us a hint what the reason could be for this problem? Is it the inheritance of the Java Types from one abstract type? Does sequence number caching play a role (we used a preallocation size of 500 and of 1 - with the same negative effect).
If you need additional information, don't hesitate to drop me a notice.
Thanks,
Andreas.

Answer 1

Each time the application using TopLink starts it will lazily acquire the next pre-allocation batch of values from the database.
You will see SQL entries like:
UPDATE SEQUENCE SET SEQ_COUNT = SEQ_COUNT + 50 WHERE SEQ_NAME = 'EMP_SEQ'
SELECT SEQ_COUNT FROM SEQUENCE WHERE SEQ_NAME = 'EMP_SEQ'
TopLink will increment the table's value and then use the values from 1 greater then initial value up to and including the value it just incremented the row to.
In your example you should see, after re-starting the server, the next value to be 501.
What exact version of TopLink are you using?
When you enable SQL logging what statement do you see executed, related to the sequence table prior to the invalid INSERT?
Doug