# Setting up logical replication for your Aurora PostgreSQL DB cluster
<a name="AuroraPostgreSQL.Replication.Logical.Configure"></a>

Setting up logical replication requires `rds_superuser` privileges. Your Aurora PostgreSQL DB cluster must be configured to use a custom DB cluster parameter group so that you can set the necessary parameters as detailed in the procedure following. For more information, see [DB cluster parameter groups for Amazon Aurora DB clusters](USER_WorkingWithDBClusterParamGroups.md). 

**To set up PostgreSQL logical replication for an Aurora PostgreSQL DB cluster**

1. Sign in to the AWS Management Console and open the Amazon RDS console at [https://console.aws.amazon.com/rds/](https://console.aws.amazon.com/rds/).

1. In the navigation pane, choose your Aurora PostgreSQL DB cluster.

1. Open the **Configuration** tab. Among the Instance details, find the **Parameter group** link with **DB cluster parameter group** for **Type**.

1. Choose the link to open the custom parameters associated with your Aurora PostgreSQL DB cluster. 

1. In the **Parameters** search field, type `rds` to find the `rds.logical_replication` parameter. The default value for this parameter is `0`, meaning that it's turned off by default. 

1. Choose **Edit parameters** to access the property values, and then choose `1` from the selector to turn on the feature. Depending on your expected usage, you might also need to change the settings for the following parameters. However, in many cases, the default values are sufficient. 
   + `max_replication_slots` – Set this parameter to a value that's at least equal to your planned total number of logical replication publications and subscriptions. If you are using AWS DMS, this parameter should equal at least your planned change data capture tasks from the cluster, plus logical replication publications and subscriptions. 
   + `max_wal_senders` and `max_logical_replication_workers` – Set these parameters to a value that's at least equal to the number of logical replication slots that you intend to be active, or the number of active AWS DMS tasks for change data capture. Leaving a logical replication slot inactive prevents the vacuum from removing obsolete tuples from tables, so we recommend that you monitor replication slots and remove inactive slots as needed. 
   + `max_worker_processes` – Set this parameter to a value that's at least equal to the total of the `max_logical_replication_workers`, `autovacuum_max_workers`, and `max_parallel_workers` values. On small DB instance classes, background worker processes can affect application workloads, so monitor the performance of your database if you set `max_worker_processes` higher than the default value. (The default value is the result of `GREATEST(${DBInstanceVCPU*2},8}`, which means that, by default, this is either 8 or twice the CPU equivalent of the DB instance class, whichever is greater).
**Note**  
You can modify parameter values in a customer-created DB parameter group. you can't change the parameter values in a default DB parameter group.

1. Choose **Save changes**.

1. Reboot the writer instance of your Aurora PostgreSQL DB cluster so that your changes takes effect. In the Amazon RDS console, choose the primary DB instance of the cluster and choose **Reboot** from the **Actions** menu. 

1. When the instance is available, you can verify that logical replication is turned on, as follows. 

   1. Use `psql` to connect to the writer instance of your Aurora PostgreSQL DB cluster.

      ```
      psql --host=your-db-cluster-instance-1.aws-region.rds.amazonaws.com --port=5432 --username=postgres --password --dbname=labdb
      ```

   1. Verify that logical replication has been enabled by using the following command.

      ```
      labdb=> SHOW rds.logical_replication;
       rds.logical_replication
      -------------------------
       on
      (1 row)
      ```

   1. Verify that the `wal_level` is set to `logical`. 

      ```
      labdb=> SHOW wal_level;
        wal_level
      -----------
       logical
      (1 row)
      ```

For an example of using logical replication to keep a database table synchronized with changes from a source Aurora PostgreSQL DB cluster, see [Example: Using logical replication with Aurora PostgreSQL DB clusters](AuroraPostgreSQL.Replication.Logical.PostgreSQL-Example.md).