> ## Documentation Index
> Fetch the complete documentation index at: https://clickhouse.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Sync to ClickHouse with WalShadow
> Replicate your Postgres data to ClickHouse with WalShadow, a native replication engine that reads directly from the PostgreSQL WAL
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`WalShadow` is a native replication engine for ClickHouse Managed Postgres that reads directly from the PostgreSQL Write-Ahead Log (WAL). It is optimized for lower latency and high-throughput workloads, delivering sub-second replication lag from Postgres to ClickHouse. It is developed in the open at [ClickHouse/walshadow](https://github.com/ClickHouse/walshadow).
`WalShadow` is one of two replication methods available under **Sync to ClickHouse**. The other, [ClickPipes](/docs/cloud/managed-postgres/clickpipes), is a fully managed data pipeline. Choose `WalShadow` when you need the lowest latency and the least replication overhead.
When `WalShadow` is available for your service, a **Private Preview** banner appears on the **Overview** page. Click **Configure WalShadow** to get started.
Before you proceed, ensure that your Postgres service is accessible to ClickHouse. `WalShadow` connects to your destination ClickHouse service directly, so you will need a ClickHouse user and password with permission to create databases and tables.
To set up replication, click **Sync to ClickHouse** in the sidebar of your Postgres instance, then click **Replicate data in ClickHouse**.
Choose **WalShadow** as the replication engine, then click **Next**.
Fill in the replication settings:
* **ClickHouse service**: Select an existing ClickHouse service or create a new one
* **Postgres database**: Select the source database to replicate from, or create a new one
* **Replication method**: Choose one of:
* **Initial load + CDC**: Import existing data and keep tables updated with new changes (recommended)
* **Initial load only**: One-time import of existing data with no ongoing updates
* **CDC only**: Skip the initial import and only capture new changes going forward
Click **Next** to proceed.
Choose a destination database and select which tables to replicate:
* **Destination database**: Select an existing ClickHouse database or create a new one
* **Tables**: Expand each schema and select individual tables, or toggle **Select all tables**. For each table you can customize the **Destination table name** and adjust **Column settings**.
* **ClickHouse user** and **ClickHouse password**: `WalShadow` connects to the destination ClickHouse service directly, so it needs credentials with permission to create the target database and tables.
Click **Replicate data to ClickHouse** to start the replication.
After you start replication, `WalShadow` appears on the **Sync to ClickHouse** page. Its status is **Creating** while the pipeline is being provisioned and the initial load is prepared.
Once provisioning completes, the status changes to **Running**. The page reports live metrics for the replication:
* **Status**: The current state of the pipeline (for example, `Running`)
* **Rows synced**: The total number of rows replicated to ClickHouse
* **Backfills pending**: The number of tables still waiting for their initial load
* **Lag**: The volume of WAL data still to be applied
* **Lag time**: How far behind Postgres the destination currently is
* **Uptime**: How long the pipeline has been running
* **Last updated**: When the metrics were last reported
Caveats
A few things to note while `WalShadow` is in Private Preview:
* Only one `WalShadow` per Postgres service for now.
* Operations and more detailed metrics are on the roadmap.