NOCYCLE

The NOCYCLE option in Oracle sequences defines the behavior of the sequence when it reaches its maximum (MAXVALUE) or minimum (MINVALUE) value. When the sequence is set with NOCYCLE, it will stop generating new values once it reaches the defined limit. Unlike the CYCLE option, which allows the sequence to restart, the NOCYCLE option prevents wrapping around.

What is the NOCYCLE Option?

• NOCYCLE is the default behavior for Oracle sequences.
• When you create or alter a sequence with NOCYCLE, the sequence will not restart once it reaches its MAXVALUE (for ascending sequences) or MINVALUE (for descending sequences).
• Once the sequence reaches its boundary value, it will stop and raise an error if a subsequent NEXTVAL is requested.

In short, with NOCYCLE, the sequence will not continue after hitting its limits.

Syntax for NOCYCLE in a Sequence

CREATE SEQUENCE sequence_name

  START WITH starting_value

  INCREMENT BY increment_value

  [MINVALUE min_value]

  [MAXVALUE max_value]

  NOCYCLE;

Example: Creating a Sequence with NOCYCLE

CREATE SEQUENCE seq_example

  START WITH 1

  INCREMENT BY 1

  MAXVALUE 5

  NOCYCLE;

In this example:

• The sequence starts at 1 and increments by 1.
• The maximum value (MAXVALUE) is set to 5.
• Once the sequence reaches 5, it will stop because the NOCYCLE option is used.

Key Concepts

1. Behavior of NOCYCLE with Ascending Sequences:

• For ascending sequences, once the sequence reaches the MAXVALUE, it will stop. Any subsequent call to NEXTVAL will result in an error.
• Example:

CREATE SEQUENCE seq_example

  START WITH 1

  INCREMENT BY 1

  MAXVALUE 5

  NOCYCLE;

This will generate values 1, 2, 3, 4, 5, and then it will stop. Attempting to get the next value with NEXTVAL will raise an error.

2. Behavior of NOCYCLE with Descending Sequences:

• For descending sequences, once the sequence reaches the MINVALUE, it will stop. Any subsequent call to NEXTVAL will raise an error.
• Example:

CREATE SEQUENCE seq_example

  START WITH 10

  INCREMENT BY -1

  MINVALUE 1

  NOCYCLE;

This will generate values 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, and then it will stop. Attempting to get the next value with NEXTVAL will result in an error.

3. No Automatic Restart with NOCYCLE:

• Unlike CYCLE, which wraps the sequence back to the START WITH value after reaching the MAXVALUE (or MINVALUE), the NOCYCLE option prevents the sequence from restarting. Once the limit is reached, the sequence will not generate new values.

4. Error Behavior After Limit Reached:

• When the sequence reaches the limit, and NOCYCLE is enabled, an error is raised. For example:

·        SELECT seq_example.NEXTVAL FROM dual;  -- Will generate 1, 2, 3, 4, 5

·        SELECT seq_example.NEXTVAL FROM dual;  -- ERROR: ORA-02287: sequence number is beyond MAXVALUE

• Oracle will raise the error ORA-02287: sequence number is beyond MAXVALUE (or MINVALUE for descending sequences) when attempting to generate a value beyond the limit.

Use Cases for NOCYCLE

1. Fixed-Range Sequences:

• NOCYCLE is ideal when you need a finite range of numbers and don’t want the sequence to restart or cycle. For example, you might use NOCYCLE when generating a sequence of unique identifiers for a specific set of records where no further values should be generated once the limit is reached.

2. Preventing Overflow or Wraparound:

• If you have a sequence of numbers with a defined upper limit and want to ensure it does not overflow or restart, NOCYCLE guarantees that the sequence will stop once it reaches its maximum value, preventing accidental wraparound.

3. Applications that Require a One-Time Use of Sequence Values:

• If you want to use the sequence for a one-time process (such as batch job IDs, invoice numbers, or temporary records), NOCYCLE ensures that no values will be repeated or cycled once the sequence limit is reached.

Important Notes on NOCYCLE

1. Default Behavior:
• By default, Oracle sequences are created with NOCYCLE. If you don’t explicitly specify CYCLE or NOCYCLE, the sequence will have the NOCYCLE behavior.
2. Changing to NOCYCLE:
• If you initially create a sequence with CYCLE, you cannot change it directly to NOCYCLE using an ALTER statement. You would need to drop and recreate the sequence with NOCYCLE specified.
3. Handling Errors with NOCYCLE:
• Be prepared for the ORA-02287 error when trying to fetch NEXTVAL after the sequence has reached its boundary with NOCYCLE in place. You should have error handling in your application or logic to manage this scenario.
4. Sequence Limits:
• The sequence will stop at either the MAXVALUE (for ascending sequences) or MINVALUE (for descending sequences). These limits are determined by the data type (e.g., NUMBER, INTEGER) and can be set according to the needs of your application.
5. Sequences with NOCYCLE in High-Volume Systems:
• In high-volume environments, be cautious about sequences with NOCYCLE if the sequence is used in a system that generates a large number of records. Once the sequence reaches its limit, you may have to manually handle the situation by either archiving old records or creating new sequences.

FAQs on NOCYCLE

1. Can I modify an existing sequence to use NOCYCLE?

• No, you cannot change the CYCLE or NOCYCLE option after the sequence has been created. You would need to drop the sequence and recreate it with the new option.

2. What happens when a sequence with NOCYCLE reaches its MAXVALUE or MINVALUE?

• Once the sequence reaches its MAXVALUE (ascending) or MINVALUE (descending) with NOCYCLE, it will stop. Any attempt to retrieve the next value with NEXTVAL will result in an error (ORA-02287).

3. Is NOCYCLE the default behavior for sequences?

• Yes, NOCYCLE is the default behavior for sequences. If you don't explicitly specify CYCLE when creating a sequence, Oracle will automatically apply NOCYCLE.

4. Can NOCYCLE be used with CACHE?

• Yes, NOCYCLE works with CACHE. The CACHE option allows Oracle to pre-allocate a set of sequence values in memory for faster access, while NOCYCLE ensures the sequence stops once the maximum or minimum value is reached.

5. Can I create a sequence with both NOCYCLE and a very large MAXVALUE?

• Yes, you can specify a very large MAXVALUE with NOCYCLE. However, once the sequence reaches the MAXVALUE, it will stop generating new values, even if the MAXVALUE is very large.

6. Can NOCYCLE be used in both ascending and descending sequences?

• Yes, NOCYCLE can be used with both ascending and descending sequences. For ascending sequences, it stops at the MAXVALUE, and for descending sequences, it stops at the MINVALUE.

 

Conclusion

The NOCYCLE option is useful when you want your Oracle sequence to generate values within a fixed range and stop once the limit is reached. It ensures that the sequence will not wrap around or continue generating values, making it ideal for applications where unique or finite sets of values are required. It’s particularly useful for one-time processes, generating unique identifiers for a specific range, or for preventing overflow in systems where sequence values have strict boundaries.