# Update PostgreSQL Replication Mode

With the `PATCH` request, you can update the replication mode of the PostgreSQL cluster.

{% hint style="warning" %}
**Note:**

* PostgreSQL deprecates `SYNCHRONOUS` replication mode for new clusters.
* You can update the existing clusters from `SYNCHRONOUS` mode to either `ASYNCHRONOUS` or\
  `STRICTLY_SYNCHRONOUS` using this API.
  {% endhint %}

## Which replication mode to choose?

* Use `ASYNCHRONOUS` when you prioritize write performance and can tolerate potential data loss on failover.
* Use `STRICTLY_SYNCHRONOUS` when data durability is critical, and you have at least 3 replicas.

## What are the potential impacts of switching replication modes?

* Switching to `ASYNCHRONOUS` from `SYNCHRONOUS` mode should not pose any downtime.
* If you are using an `ASYNCHRONOUS` or `SYNCHRONOUS` cluster with less than 3 replicas and you decide to switch to the `STRICTLY_SYNCHRONOUS` mode (which requires 3 replicas at least),
  * You might experience some time where the DB is read-only.
  * The downtime is because the replication mode on writes needs confirmation from at least one synchronous-standby, and the primary is not allowed to continue in the standalone mode. For more information, see [<mark style="color:blue;">Replication Mode</mark>](https://docs.ionos.com/sections-test/guides/databases/overview/high-availability#replication-modes).

{% hint style="info" %}
**Important:** If you are switching to `STRICTLY_SYNCHRONOUS` mode, we recommend:

* Performing the replication mode switch outside of the critical business hours.
* You should first update to 3 replicas, wait for them to be ready, and only then change to `STRICTLY_SYNCHRONOUS` mode.
  {% endhint %}

## Endpoint

Use the following endpoint to update the replication mode for an existing PostgreSQL cluster:`https://api.ionos.com/databases/postgresql/clusters/{clusterId}`

{% hint style="info" %}
**Note:** The sample UUID is `498ae72f-411f-11eb-9d07-046c59cc737e`.
{% endhint %}

## Request

```bash
curl --include \
    --request PATCH \
    --user "clientname@ionos.com:xxxxxx" \
    --header "Content-Type: application/json" \
    --data-binary '{
      "metadata": {},
      "properties": {
        "synchronizationMode": "ASYNCHRONOUS"
      }
    }' \
    https://api.ionos.com/databases/postgresql/clusters/498ae72f-411f-11eb-9d07-046c59cc737e
```

## Response

```json
{
  "type": "cluster",
  "id": "498ae72f-411f-11eb-9d07-046c59cc737e",
  "metadata": {
    "state": "AVAILABLE",
    "createdDate": "2020-12-10T12:37:50.000Z",
    "createdBy": "clientname@ionos.com",
    "createdByUserId": "012342f-411f-1eeb-9d07-046c59cc737e",
    "lastModifiedDate": "2020-12-18T21:37:50.000Z",
    "lastModifiedBy": "clientname@ionos.com",
    "lastModifiedByUserId": "012342f-411f-1eeb-9d07-046c59cc737e"
  },
  "properties": {
        "displayName": "an even better name",
        "location": "de/txl",
        "dnsName": "pg-pgov71sjg1c875ji.postgresql.de-txl.ionos.com",
        "connections": [
            {
                "datacenterId": "db7e8811-cfae-4b40-82ee-2f4cff81e105",
                "lanId": "2",
                "cidr": "10.7.222.3/23"
            }
        ],
        "cores": 4,
        "postgresVersion": "15",
        "ram": 4096,
        "instances": 1,
        "storageSize": 102400,
        "storageType": "HDD",
        "maintenanceWindow": {
            "dayOfTheWeek": "Sunday",
            "time": "03:30:00"
        },
        "synchronizationMode": "ASYNCHRONOUS",
        "connectionPooler": {
            "enabled": false,
            "poolMode": "transaction"
        }
    }
}
```