In PostgreSQL, a commonly faced error “nextval: reached maximum value” error occurs when a sequence reaches its maximum value and the user is still trying to generate a new value. Postgres offers various methods to deal with the stated issue, such as resetting the sequence, altering the maximum value of the sequence, repeating the sequence, and so on.
This post will explain some useful methods to rectify the “nextval: reached maximum value” error in PostgreSQL.
How to Fix the “nextval: reached a maximum value of sequence” Error in Postgres?
We have created a sequence name example_seq whose details are enlisted in the following snippet:
\d example_seq;
Let’s execute the nextval() function to see how the stated error occurs in Postgres:
SELECT nextval('example_seq');
To fix the “nextval: reached a maximum value” error, the below-listed approaches can be used in Postgres:
- Method 1: Use Cycle Option
- Method 2: Alter the Sequence Maximum Value
- Method 3: Remove the MAXVALUE Option From the Sequence
- Method 4: RESTART the Sequence
Method 1: Use Cycle Option
Specifying the cycle option will restart the sequence once it reaches the maximum limit:
ALTER SEQUENCE example_seq CYCLE;
Let’s confirm the sequence structure using the following command:
\d example_seq;
The output confirms that the “CYCLE” option has been enabled successfully. Let’s run the nextval() function once more:
SELECT nextval('example_seq');
The output shows that the sequence has been restarted from the starting value.
Method 2: Alter the Sequence Maximum Value
Increasing the maximum value of the sequence will also rectify the stated error:
ALTER SEQUENCE example_seq MAXVALUE 500;
Now the stated error wouldn’t appear until the sequence reaches the specified maximum value.
Method 3: Remove the MAXVALUE Option From the Sequence
Removing the MAXVALUE option from the sequence will set the maximum value to the default(i.e. Default maximum value of the specified data type).
ALTER SEQUENCE example_seq NO MAXVALUE;
In this case, the stated error wouldn’t appear until the sequence reaches the maximum value of the specified data type.
Method 4: RESTART the Sequence
Resetting the sequence value will restart the sequence from the beginning. To do this, utilize the ALTER SEQUENCE command with the RESTART argument:
ALTER SEQUENCE example_seq RESTART;
The output verifies that the sequence has been reset successfully.
Conclusion
In PostgreSQL, a commonly faced error “nextval: reached maximum value” error occurs when a sequence reaches its maximum value and the user is still trying to generate a new value. In Postgres, various methods such as the “Cycle” option, “Altering the Maximum Value”, “Removing the MAXVALUE” option, and RESTART option are used. This post has provided several methods to fix the “nextval: reached maximum value” error in PostgreSQL.
