How Do I Resynchronize a PostgreSQL Primary Key Sequence Out of Sync with Table Rows?

Resolving PostgreSQL Primary Key Sequence Conflicts

Data insertion failures due to duplicate key errors often indicate a primary key sequence out of sync with the table's rows. This typically occurs after database import or restore processes. Here's how to rectify this:

1. Confirm Sequence Imbalance:

   First, determine the highest existing ID:

   <code class="language-sql">SELECT MAX(id) FROM your_table;</code>

2. Examine the Next Sequence Number:

   Next, check the sequence's next value:

   <code class="language-sql">SELECT nextval('your_table_id_seq');</code>

   If the sequence value is less than the table's maximum ID, synchronization is required.

3. Begin Transaction:

   Wrap the correction within a transaction for data integrity:

   <code class="language-sql">BEGIN;</code>

4. Exclusive Table Lock:

   To prevent concurrent modifications, exclusively lock the table:

   <code class="language-sql">LOCK TABLE your_table IN EXCLUSIVE MODE;</code>

5. Adjust Sequence Value:

   Use this command to update the sequence:

   <code class="language-sql">SELECT setval('your_table_id_seq', GREATEST((SELECT MAX(your_id) FROM your_table), (SELECT nextval('your_table_id_seq') - 1)));</code>

   This sets the sequence to the larger of the table's maximum ID or the current sequence value minus one.

6. Commit Transaction:

   Finalize the changes:

   <code class="language-sql">COMMIT;</code>

7. Release Table Lock:

   The table lock is automatically released after the transaction commits.

Following these steps ensures the primary key sequence aligns with the table data, eliminating future duplicate key errors during insertions.

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