In Materialize, a [cluster](/concepts/clusters/) is an isolated environment,
similar to a virtual warehouse in Snowflake. When you create a cluster, you
choose the size of its compute resource allocation based on the work you need
the cluster to do, whether ingesting data from a source, computing
always-up-to-date query results, serving results to external clients, or a
combination.

In this step, you'll create a dedicated cluster for ingesting source data from
your PostgreSQL database.

1. In the [SQL Shell](https://console.materialize.com/), or your preferred SQL
   client connected to Materialize, use the [`CREATE CLUSTER`](/sql/create-cluster/)
   command to create the new cluster:

    ```mzsql
    CREATE CLUSTER ingest_postgres (SIZE = '50cc');

    SET CLUSTER = ingest_postgres;
    ```

    A cluster of [size](/sql/create-cluster/#size) `50cc` should be enough to
    accommodate multiple PostgreSQL sources, depending on the source
    characteristics (e.g., sources with [`ENVELOPE UPSERT`](/sql/create-source/#upsert-envelope)
    or [`ENVELOPE DEBEZIUM`](/sql/create-source/#debezium-envelope) will be more
    memory-intensive) and the upstream traffic patterns. You can readjust the
    size of the cluster at any time using the [`ALTER CLUSTER`](/sql/alter-cluster) command:

    ```mzsql
    ALTER CLUSTER <cluster_name> SET ( SIZE = <new_size> );
    ```