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Status Future consideration
Workspace IBM i
Categories Db2 for i
Created by Guest
Created on Nov 3, 2016

DB2 Next Identity Value has incorrect value

The majority of new tables we create contain a record identity column defined as GENERATED BY DEFAULT, starting at 1, increment by 1. This column is also the primary key for the tables.

Most inserts into tables do not specify a value for the record identity column. This causes DB2 to use the stored next identity value as the record identity of the inserted record. After the insert DB2 increments the next identity value based on the rules defined for the column.

A simple example. New table is empty and next identity value is 1. Ten records are inserted into the table. Next identity value is now 11. Perfect. The next record inserted will have a primary key of 11. The next identity value is incremented to 12.

A special situation arises that requires records to be inserted and the record identity value to be provided. For example, records with primary keys of 13 and 14 are inserted into the table. The record identity of each record inserted is greater than the DB2 next identity value.

After the records 13 and 14 are inserted the next identity value is still 12, not the expected 15. (14 + 1).

All subsequent inserts which do not specify a record identity value will fail. DB2 uses 12 for the insert which is used in an existing record.

At this point an ALTER TABLE ALTER COLUMN statement must be used to correct DB2's next identity value. This can be problematic if the table in question is highly used since an exclusive lock is required. Compounding this problem the alter table statement requires a numeric literal as the next identity value. It's possible to miskey the new value which can lead to more problems.

DB2 should correctly update the next identity value when an insert provides a record identity value that is greater than the current next identity value.

DB2 should not allow a RESTART WITH value that conflicts with existing record values.

Use Case:

Normal record inserts work as expected.

Special record inserts with record identity values specified require off hours processing:
1. Allocate the table(s)
2. Insert records with specified record identity values
3. Retrieve list of DB2's next identity value for the table(s)
4. Execute ALTER TABLE table_name ALTER COLUMN record_id RESTART WITH correct_next_identity_value for each table
5. Deallocate the table(s)

Idea priority Medium
  • Guest
    Apr 28, 2021

    IBM will use this request as input to planning but no commitment is made or implied. This request will be updated in the future if IBM implements it.

  • Guest
    Nov 16, 2018

    This RFE is fine, but there could be a tiny change to get more out:
    Change the ALTER TABLE mySchema.myTable ALTER COLUMN myIdColumn RESTART WITH instead of using a numeric value;

    We can code around this issue with a RPG-Command and something like that, but its more efficient, if IBM deliver the correct way. And this "max-Thing" works, but it is not correct.