> ## Documentation Index
> Fetch the complete documentation index at: https://artie.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Replicate PostgreSQL tables without primary keys

> Configure PostgreSQL tables without primary keys for replication by using REPLICA IDENTITY FULL and an Artie primary key override.

You can replicate a PostgreSQL table without adding a database primary-key constraint. Configure PostgreSQL to include the complete previous row in change events, then tell Artie which existing unique index to use to identify each row.

## What you'll need

* A PostgreSQL table with no primary key
* An existing unique index, or columns that you can make unique, to identify each row
* Permission to alter the source table's replica identity

<Warning>
  Choose columns that uniquely identify every row. Artie uses the selected columns to merge updates and deletes in the destination. Do not use columns with duplicate values.
</Warning>

## Configure the table

<Steps>
  <Step title="Create or identify a unique index">
    Artie requires the override columns to match a unique index on the source table. If you want to turn an existing column into an actual unique constraint, first run this check. It must return no rows:

    ```sql theme={null}
    -- Find duplicate values before adding the constraint.
    SELECT external_id, count(*) AS duplicate_count
    FROM public.orders
    WHERE external_id IS NOT NULL
    GROUP BY external_id
    HAVING count(*) > 1;
    ```

    Then run the following outside a transaction block. The index build does not block inserts, updates, or deletes. The final `ALTER TABLE` is brief and fails after five seconds rather than waiting on a conflicting lock.

    ```sql theme={null}
    -- Fail quickly instead of waiting on a conflicting lock.
    SET lock_timeout = '5s';

    -- Build the backing unique index without blocking normal writes.
    CREATE UNIQUE INDEX CONCURRENTLY orders_external_id_key
    ON public.orders (external_id);

    -- Convert the index into an actual unique constraint.
    ALTER TABLE public.orders
    ADD CONSTRAINT orders_external_id_unique
    UNIQUE USING INDEX orders_external_id_key;
    ```

    For a composite identifier, create one unique index containing all of the columns you will select in Artie.
  </Step>

  <Step title="Set the table replica identity to FULL">
    Run the following as the table owner or another role with permission to alter the table:

    ```sql theme={null}
    ALTER TABLE public.orders REPLICA IDENTITY FULL;
    ```

    `REPLICA IDENTITY FULL` makes PostgreSQL include the full previous row in update and delete events, which lets Artie use the override columns when the table has no primary key.

    <Note>
      This setting can increase WAL volume for updates and deletes because PostgreSQL records the full old row. Monitor replication-slot usage after enabling it.
    </Note>
  </Step>

  <Step title="Add the table and set the primary key override in Artie">
    In the Artie dashboard, open your pipeline, then go to **Edit** > **Tables**. Add or select the table, open **Table settings**, and choose the **Advanced settings** tab.

    Enable **Override primary keys** and select the column or columns from the unique index. For the example above, select `external_id`.

    Keep the selected columns included in replication. Artie uses them as the table's merge key in the destination.
  </Step>

  <Step title="Save, deploy, and verify">
    Save the table settings and deploy the pipeline. Verify an insert, update, and delete on the source table are reflected in the destination.
  </Step>
</Steps>

## When to add a database primary key instead

Use a real PostgreSQL primary key when you control the schema and can add one safely. A primary key is the simplest long-term choice. Use the override workflow when you cannot change the table's primary-key constraint but it already has a stable unique identifier.