CREATE SOURCE: PostgreSQL (New Syntax)

Creates a new source from PostgreSQL. Materialize supports creating sources from PostgreSQL version 11+. Once a new source is created, you can CREATE TABLE FROM SOURCE to create the corresponding tables in Materialize and start the data ingestion process.

PostgreSQL 16+ is required for connecting Materialize to a physical replica.

Prerequisites

To create a source from PostgreSQL 11+, you must first:

• Configure upstream PostgreSQL instance
  • Set up logical replication.
  • Create a publication.
  • Create a replication user and password for Materialize to use to connect.
• Configure network security
  • Ensure Materialize can connect to your PostgreSQL instance.
• Create a connection to PostgreSQL in Materialize
  • The connection setup depends on the network security configuration.

For details, see the PostgreSQL integration guides.

Syntax

To create a source from an external PostgreSQL:

CREATE SOURCE [IF NOT EXISTS] <source_name>
[IN CLUSTER <cluster_name>]
FROM POSTGRES CONNECTION <connection_name> (PUBLICATION '<publication_name>')
[WITH ( <with_option> [, ...] )]
;

Details

Ingesting data

After a source is created, you can create tables from the source, referencing the tables in the publication, to start ingesting data. You can create multiple tables that reference the same table in the publication.

See CREATE TABLE FROM SOURCE for details.

Handling table schema changes

The use of the CREATE SOURCE with the new CREATE TABLE FROM SOURCE allows for the handling of certain upstream DDL changes without downtime.

See CREATE TABLE FROM SOURCE for details.

See also Handling upstream operations for additional upstream operation considerations.

Supported types

With the new syntax, after a PostgreSQL source is created, you CREATE TABLE FROM SOURCE to create a corresponding table in Materialize and start ingesting data.

Materialize natively supports the following PostgreSQL types (including the array type for each of the types):

• bool
• bpchar
• bytea
• char
• date
• daterange
• float4
• float8
• int2
• int2vector
• int4
• int4range
• int8
• int8range
• interval
• json
• jsonb
• numeric
• numrange
• oid
• text
• time
• timestamp
• timestamptz
• tsrange
• tstzrange
• uuid
• varchar

For more information, including strategies for handling unsupported types, see CREATE TABLE FROM SOURCE.

Publication membership

PostgreSQL’s logical replication API does not provide a signal when users remove tables from publications. Because of this, Materialize relies on periodic checks to determine if a table has been removed from a publication, at which time it generates an irrevocable error, preventing any values from being read from the table.

However, it is possible to remove a table from a publication and then re-add it before Materialize notices that the table was removed. In this case, Materialize can no longer provide any consistency guarantees about the data we present from the table and, unfortunately, is wholly unaware that this occurred.

To mitigate this issue, if you need to drop and re-add a table to a publication, ensure that you remove the table/subsource from the source before re-adding it using the DROP SOURCE command.

PostgreSQL replication slots

When you define a source, Materialize will automatically create a replication slot in the upstream PostgreSQL database (see PostgreSQL replication slots). Each source ingests the raw replication stream data for all tables in the specified publication using a single replication slot. This allows you to minimize the performance impact on the upstream database as well as reuse the same source across multiple materializations.

The name of the replication slot created by Materialize is prefixed with materialize_. In Materialize, you can query the mz_internal.mz_postgres_sources to find the replication slots created:

SELECT id, replication_slot FROM mz_internal.mz_postgres_sources;

    id   |             replication_slot
---------+----------------------------------------------
  u8     | materialize_7f8a72d0bf2a4b6e9ebc4e61ba769b71

Reading from a physical standby

Materialize can replicate from a PostgreSQL physical standby (read replica) instead of the primary, using logical decoding on the standby. This requires PostgreSQL 16+ on both the primary and the standby, since earlier versions do not support creating logical replication slots on a standby.

When the upstream is a standby, the replication slot is created on the standby and Materialize only connects to the standby. Note that slot creation on a standby can block until the primary emits a standby snapshot (a RUNNING_XACTS WAL record). On an idle primary, run SELECT pg_log_standby_snapshot() on the primary to unblock source creation.

Handling upstream operations

This section describes how changes to upstream tables that Materialize ingests affect the corresponding Materialize tables.

Adding a column

When you add a new column to your upstream table, Materialize continues to ingest only the existing columns.

To incorporate the new column:

• If using the new CREATE SOURCE and CREATE TABLE FROM SOURCE syntax, create a new table from the source. See Handle upstream column addition.

• If using the legacy CREATE SOURCE ... FOR ... syntax that creates subsources, use DROP SOURCE to drop the affected subsource, and then add the table back to the source using ALTER SOURCE ... ADD SUBSOURCE. The re-added subsource includes the new column.

Dropping a column

Dropping columns that Materialize does not ingest (for example, columns added after the source was created, or columns that are excluded) is supported. As these columns were never ingested, you can drop them without issue.

If your Materialize source ingests a column, dropping that column from your upstream table puts the affected table into an error state.

• If using the new CREATE SOURCE and CREATE TABLE FROM SOURCE syntax, you can safely drop a column by first ignoring it in Materialize. See Handle upstream column drop.

• If using legacy CREATE SOURCE ... FOR ... syntax, use DROP SOURCE to drop the affected subsource, and then add the table back to the source using ALTER SOURCE ... ADD SUBSOURCE.

Changing constraints

Materialize ignores the following constraint changes: foreign key, CHECK, and EXCLUSION. As such, you can add or drop them without affecting ingestion.

Materialize also ignores NOT NULL, UNIQUE, and PRIMARY KEY constraints that are added after the Materialize table is created (that is, the table was created without them). Adding such a constraint, and later dropping it, does not affect ingestion.

Dropping a NOT NULL, UNIQUE, or PRIMARY KEY constraint that existed when the table was created puts the affected table into an error state.

If using the new CREATE SOURCE and CREATE TABLE FROM SOURCE syntax, you can safely drop such a constraint by first excluding it in Materialize. See Handle upstream constraint drop.

Changing a column’s data type

Changing an ingested column’s data type upstream puts the affected Materialize table into an error state unless the column was ingested as text via the TEXT COLUMNS option. Ingestion for that table stops, and you must drop and recreate the table in Materialize to resume ingestion.

Renaming a column

Renaming a column that Materialize ingests puts the affected table into an error state. Ingestion for that table stops, and you must drop and recreate the table in Materialize to resume ingestion.

Table-level operations

The following upstream operations put the affected table into an error state. Ingestion for that table stops, and you must drop and recreate the affected table in Materialize to resume:

• Dropping a table (DROP TABLE), or removing it from the publication (ALTER PUBLICATION ... DROP TABLE).
• Renaming a table or moving it to a different schema.
• Setting a table’s replica identity to anything other than FULL (ALTER TABLE ... REPLICA IDENTITY).
• Truncating a table (TRUNCATE). To clear a table without putting it into an error state, use an unqualified DELETE FROM t; instead.

Source failure states and recovery

Operations that do not require re-creating the source

Materialize tracks a log sequence number (LSN) as it consumes the upstream write-ahead log (WAL), and the source’s replication slot retains the WAL that Materialize has not yet consumed. Because the slot outlives the connection, routine operational events do not lose data: after a transient interruption the source stalls, then resumes from its committed LSN and catches up automatically. No action is required for the following operations:

• Restarting or patching PostgreSQL (including OS-level restarts).
• Restarting Materialize. The source resumes from its committed LSN and does not re-snapshot already-ingested data.
• Transient network interruptions between Materialize and PostgreSQL. These surface as connection closed.
• Resizing the cluster that hosts the source, or changing its replication factor. Briefly, the source may report replication slot ... is active while the upstream releases the slot from the previous connection.
• The upstream database running out of disk space, once space is freed.

Operations that require re-creating the source

A smaller set of events breaks LSN continuity or destroys the replication slot. When this happens, Materialize cannot guarantee a correct, gap-free view of your data. Most of these put the entire source into an error or permanently stalled state. One, restoring from a volume or disk snapshot, cannot be detected at all, so the source keeps running on diverged data. Every event in this section requires re-creating the source. Upstream changes to an individual table’s schema are handled separately, and do not error the entire source.

In each case below, the remediation is to drop and re-create the source:

DROP SOURCE mz_source CASCADE;

CREATE SOURCE mz_source
  FROM POSTGRES CONNECTION pg_connection (PUBLICATION 'mz_source');

-- Re-create the tables you were ingesting.
CREATE TABLE table_1 FROM SOURCE mz_source (REFERENCE public.table_1);

If you are using the legacy CREATE SOURCE ... FOR TABLES syntax, re-create the source with the same FOR TABLES list instead of adding tables separately.

Because a re-created source snapshots from the current state of the upstream database, any changes it missed while it was in an error state are reflected in the snapshot rather than replayed as individual updates.

Point-in-time restore

Restoring the source database from a backup, including restoring to a different server for disaster recovery, increments the PostgreSQL timeline and is detected as a discontinuity. The source fails with an error of the form:

unsupported action: database restored from point-in-time backup. Expected
timeline ID 8 but got 9

The same error covers other events that change the timeline, such as a managed failover between replicas. To see the timeline a source is pinned to, query mz_internal.mz_postgres_sources:

SELECT s.name, p.replication_slot, p.timeline_id
FROM mz_internal.mz_postgres_sources p
JOIN mz_catalog.mz_sources s ON s.id = p.id;

If your upstream fails over between replicas as part of routine maintenance, see High-availability failovers.

Restoring from a volume or disk snapshot

Restoring the upstream data directory from a crash-consistent volume or disk snapshot rolls the database back, but preserves the timeline ID and the replication slot. Materialize cannot detect this kind of restore. The source keeps running without an error, but its contents diverge from upstream. This can surface later as incorrect results, or as negative-accumulation errors in queries such as Non-positive multiplicity.

Promotion of a physical replica

When a source reads from a physical standby (read replica) rather than the primary, promoting that standby to a primary fails the source with:

unsupported action: upstream physical replica status changed (e.g. a physical
replica was promoted to a primary). Expected pg_is_in_recovery()=true but got
false

Materialize detects the promotion while the replication stream is live, without waiting for a restart. Re-create the source against the promoted node.

Replication slot invalidated

PostgreSQL invalidates a replication slot once the WAL it holds exceeds max_slot_wal_keep_size. This protects the upstream from running out of disk, at the cost of ending replication. The source fails with:

replication slot has been invalidated because it exceeded the maximum reserved
size

To avoid this, size the source cluster so that it keeps up with the upstream write rate, and set max_slot_wal_keep_size high enough to cover your longest expected outage. Some hosted PostgreSQL services set this value for you and do not allow it to be raised.

Replication slot dropped or rewound

If the slot Materialize is using is dropped upstream, or the upstream is rebuilt from a base backup (which does not carry replication slots), a new slot starts at the current LSN, past the point the source needs to resume from. The source stalls with:

slot overcompacted. Requested LSN ... but only LSNs >= ... are available

For diagnosis steps, see Slot overcompacted. PostgreSQL refuses to drop a slot that is in use, so this generally happens only while the source is paused or disconnected.

Not every rewind is caught this way. A rewind that leaves the slot able to serve the LSN the source asks for, such as restoring from a volume or disk snapshot, raises no error at all.

Dropping the publication

Running DROP PUBLICATION upstream stalls the source, and all of its tables, with:

publication "mz_source" does not exist

Re-create the publication upstream, then re-create the source.

Major version upgrades

A PostgreSQL major version upgrade rewrites the on-disk format and does not preserve the replication slot, so there is no in-place recovery. To upgrade without a gap in your downstream views, run a second source against the upgraded instance in parallel and cut over once it has hydrated. See Upgrade the major version of your PostgreSQL source.

High-availability failovers

Some managed PostgreSQL services increment the timeline during routine high-availability operations, such as maintenance, a machine-tier change, or an automatic failover between replicas. Materialize cannot distinguish these from a genuine restore, so by default they fail the source with the Expected timeline ID error.

On self-managed Materialize, where the upstream service guarantees that a failover is a contiguous fork of the WAL with no data loss, you can disable timeline validation with the pg_source_validate_timeline system parameter:

ALTER SYSTEM SET pg_source_validate_timeline = false;

This parameter is not available on Materialize Cloud. There, a high-availability failover that changes the timeline requires re-creating the source.

Examples

Prerequisites

To create a source from PostgreSQL 11+, you must first:

• Configure upstream PostgreSQL instance
  • Set up logical replication.
  • Create a publication.
  • Create a replication user and password for Materialize to use to connect.
• Configure network security
  • Ensure Materialize can connect to your PostgreSQL instance.
• Create a connection to PostgreSQL in Materialize
  • The connection setup depends on the network security configuration.

For details, see the PostgreSQL integration guides.

Create a source

Once you have configured the upstream PostgreSQL, network security, and created the connection, you can create the source. In this example, the PostgreSQL publication is mz_source and the connection to PostgreSQL is pg_connection.

/* This example assumes:
- In the upstream PostgreSQL, you have defined:
  - replication user and password with the appropriate access.
  - a publication named `mz_source` for the `public.items` and `public.orders` tables.
- In Materialize:
  - You have created a secret for the PostgreSQL password.
  - You have defined the connection to the upstream PostgreSQL.
  - You have used the connection to create a source.

  For example (substitute with your configuration):
    CREATE SECRET pgpass AS '<replication user password>'; -- substitute
    CREATE CONNECTION pg_connection TO POSTGRES (
      HOST '<hostname>',          -- substitute
      DATABASE <db>,              -- substitute
      USER <replication user>,    -- substitute
      PASSWORD SECRET pgpass
      -- [, <network security configuration> ]
    );
*/

CREATE SOURCE pg_source
FROM POSTGRES CONNECTION pg_connection (
  PUBLICATION 'mz_source'
);

After a source is created, you can create tables from the source, referencing specific upstream table(s). Use a DDL transaction block to create multiple tables from the same source.

BEGIN;
CREATE TABLE items
FROM SOURCE pg_source(REFERENCE public.items)
;
CREATE TABLE orders
FROM SOURCE pg_source(REFERENCE public.orders)
;
COMMIT;

For more information, see CREATE TABLE.

Related pages

• CREATE TABLE
• CREATE SECRET
• CREATE CONNECTION
• PostgreSQL integration guides