Ingest data from Self-hosted PostgreSQL

This page shows you how to stream data from a self-hosted PostgreSQL database to Materialize using the PostgreSQL source.

Before you begin

• Make sure you are running PostgreSQL 11 or higher.

• Make sure psql is installed on your workstation.

You’ll use psql to interact with your PostgreSQL database and with Materialize.

Step 1. Enable logical replication

Materialize uses PostgreSQL’s logical replication protocol to track changes in your database and propagate them to Materialize.

As a first step, you need to make sure logical replication is enabled.

1. As a superuser, use psql to connect to your PostgreSQL database.

2. Check if logical replication is enabled:

   SHOW wal_level;
   

   The wal_level setting must be set to logical. If it’s set to any other value, change it to logical in the database configuration file (postgresql.conf).

3. Restart the database in order for the new wal_level to take effect. Keep in mind that restarting can affect database performance.

4. Back in your psql shell, verify that replication is now enabled:

   SHOW wal_level;
   

Step 2. Create a publication

Once logical replication is enabled, the next step is to create a publication with the tables that you want to replicate to Materialize. You’ll also need a user for Materialize with sufficient privileges to manage replication.

1. For each table that you want to replicate to Materialize, set the replica identity to FULL:

   ALTER TABLE <table1> REPLICA IDENTITY FULL;
   

   ALTER TABLE <table2> REPLICA IDENTITY FULL;
   

   REPLICA IDENTITY FULL ensures that the replication stream includes the previous data of changed rows, in the case of UPDATE and DELETE operations. This setting enables Materialize to ingest PostgreSQL data with minimal in-memory state. However, you should expect increased disk usage in your PostgreSQL database.

2. Create a publication with the tables you want to replicate:

   For specific tables:

   CREATE PUBLICATION mz_source FOR TABLE <table1>, <table2>;
   

   For all tables in the database:

   CREATE PUBLICATION mz_source FOR ALL TABLES;
   

   The mz_source publication will contain the set of change events generated from the specified tables, and will later be used to ingest the replication stream.

   Be sure to include only the tables you need. If the publication includes additional tables, Materialize will waste resources on ingesting and then immediately discarding the data.

3. Create a user for Materialize, if you don’t already have one:

   CREATE USER materialize PASSWORD '<password>';
   

4. Grant the user permission to manage replication:

   ALTER ROLE materialize WITH REPLICATION;
   

5. Grant the user the required permissions on the tables you want to replicate:

   GRANT CONNECT ON DATABASE <dbname> TO materialize;
   

   GRANT USAGE ON SCHEMA <schema> TO materialize;
   

   GRANT SELECT ON <table1> TO materialize;
   

   GRANT SELECT ON <table2> TO materialize;
   

   Once connected to your database, Materialize will take an initial snapshot of the tables in your publication. SELECT privileges are required for this initial snapshot.

   If you expect to add tables to your publication, you can grant SELECT on all tables in the schema instead of naming the specific tables:

   GRANT SELECT ON ALL TABLES IN SCHEMA <schema> TO materialize;
   

Step 3. Configure network security

There are various ways to configure your database’s network to allow Materialize to connect:

• Allow Materialize IPs: If your database is publicly accessible, you can configure your database’s firewall to allow connections from a set of static Materialize IP addresses.

• Use an SSH tunnel: If your database is running in a private network, you can use an SSH tunnel to connect Materialize to the database.

Select the option that works best for you.

Step 4. Create an ingestion cluster

In Materialize, a cluster 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 clients, or a combination.

In this case, you’ll create 1 new cluster containing 1 medium replica for ingesting source data from your PostgreSQL database.

1. In the psql shell connected to Materialize, use the CREATE CLUSTER command to create the new cluster:

   CREATE CLUSTER ingest_postgres SIZE = 'medium';
   

   We recommend starting with a medium size replica or larger. This will help Materialize more quickly process the initial snapshot of the tables in your publication. Once the snapshot is finished, you’ll right-size the cluster.

Step 5. Start ingesting data

Now that you’ve configured your database network and created an ingestion cluster, you can connect Materialize to your PostgreSQL database and start ingesting data. The exact steps depend on your networking configuration, so start by selecting the relevant option.

Step 6. Check the ingestion status

Before it starts consuming the replication stream, Materialize takes a snapshot of the relevant tables in your publication. Until this snapshot is complete, Materialize won’t have the same view of your data as your PostgreSQL database.

In this step, you’ll first verify that the source is running and then check the status of the snapshotting process.

1. Back in the psql shell connected to Materialize, use the mz_source_statuses table to check the overall status of your source:

   WITH
     source_id AS
     (SELECT id FROM mz_objects WHERE name = 'mz_source')
   SELECT *
   FROM
     mz_internal.mz_source_statuses
       JOIN
         (
           SELECT referenced_object_id
           FROM mz_internal.mz_object_dependencies
           WHERE
             object_id = (SELECT id FROM source_id)
           UNION SELECT id FROM source_id
         )
         AS sources
       ON mz_source_statuses.id = sources.referenced_object_id;
   

   For each subsource, make sure the status is running. If you see stalled or failed, there’s likely a configuration issue for you to fix. Check the error field for details and fix the issue before moving on. Also, if the status of any subsource is starting for more than a few minutes, contact our team.

2. Once the source is running, use the mz_source_statistics table to check the status of the initial snapshot:

   WITH
     source_id AS
     (SELECT id FROM mz_objects WHERE name = 'mz_source')
   SELECT bool_and(snapshot_committed) AS snapshot_committed
   FROM
     mz_internal.mz_source_statistics
       JOIN
         (
           SELECT referenced_object_id
           FROM mz_internal.mz_object_dependencies
           WHERE
             object_id = (SELECT id FROM source_id)
           UNION SELECT id FROM source_id
         )
         AS sources
       ON mz_source_statistics.id = sources.referenced_object_id;
   

    snapshot_committed
   --------------------
    t
   (1 row)
   

   Once snapshot_commited is t, move on to the next step. Snapshotting can take between a few minutes to several hours, depending on the size of your dataset and the size of the cluster replica you chose for your ingest_postgres cluster.

Step 7. Right-size the cluster

After the snapshotting phase, Materialize starts ingesting change events from the PostgreSQL replication stream. For this work, Materialize generally performs well with an xsmall replica, so you can resize the cluster accordingly.

1. Still in the psql shell connected to Materialize, use the ALTER CLUSTER command to downsize the cluster to xsmall:

   ALTER CLUSTER ingest_postgres SET (SIZE 'xsmall');
   

   Behind the scenes, this command adds a new xsmall replica and removes the medium replica.

2. Use the SHOW CLUSTER REPLICAS command to check the status of the new replica:

   SHOW CLUSTER REPLICAS WHERE cluster = 'ingest_postgres';
   

        cluster     | replica |  size  | ready
   -----------------+---------+--------+-------
    ingest_postgres | r1      | xsmall | t
   (1 row)
   

3. Going forward, you can verify that your new replica size is sufficient as follows:

   1. In Materialize, get the replication slot name associated with your PostgreSQL source from the mz_internal.mz_postgres_sources table:

      SELECT
          d.name AS database_name,
          n.name AS schema_name,
          s.name AS source_name,
          pgs.replication_slot
      FROM
          mz_sources AS s
          JOIN mz_internal.mz_postgres_sources AS pgs ON s.id = pgs.id
          JOIN mz_schemas AS n ON n.id = s.schema_id
          JOIN mz_databases AS d ON d.id = n.database_id;
      

   2. In PostgreSQL, check the replication slot lag, using the replication slot name from the previous step:

      SELECT
          pg_size_pretty(pg_current_wal_lsn() - confirmed_flush_lsn)
          AS replication_lag_bytes
      FROM pg_replication_slots
      WHERE slot_name = '<slot_name>';
      

      The result of this query is the amount of data your PostgreSQL cluster must retain in its replication log because of this replication slot. Typically, this means Materialize has not yet communicated back to PostgreSQL that it has committed this data. A high value can indicate that the source has fallen behind and that you might need to scale up your ingestion cluster.

Next steps

With Materialize ingesting your PostgreSQL data into durable storage, you can start exploring the data, computing real-time results that stay up-to-date as new data arrives, and serving results efficiently.

• Explore your data with SHOW SOURCES and SELECT.
• Compute real-time results in memory with CREATE VIEW and CREATE INDEX or in durable storage with CREATE MATERIALIZED VIEW.
• Serve results to a PostgreSQL-compatible SQL client or driver with SELECT or SUBSCRIBE or to an external message broker with CREATE SINK.
• Check out the tools and integrations supported by Materialize.