CREATE SUBSCRIPTION

7 SQL - Language Statements

CREATE SUBSCRIPTION

define a new subscription

    CREATE SUBSCRIPTION subscription_name
        CONNECTION 'conninfo'
        PUBLICATION publication_name [, ...]
        [ WITH ( subscription_parameter [= value] [, ... ] ) ]

## Description

`CREATE SUBSCRIPTION` adds a new logical-replication subscription. The user that creates a subscription becomes the owner of the subscription. The subscription name must be distinct from the name of any existing subscription in the current database.

A subscription represents a replication connection to the publisher. Hence, in addition to adding definitions in the local catalogs, this command normally creates a replication slot on the publisher.

A logical replication worker will be started to replicate data for the new subscription at the commit of the transaction where this command is run, unless the subscription is initially disabled.

To be able to create a subscription, you must have the privileges of the `pg_create_subscription` role, as well as `CREATE` privileges on the current database.

Additional information about subscriptions and logical replication as a whole is available at logical-replication-subscription and logical-replication.

## Parameters

`subscription_name`

- The name of the new subscription.

`CONNECTION '`conninfo`'`

- The libpq connection string defining how to connect to the publisher database. For details see libpq-connstring.

`PUBLICATION `publication_name` [, ...]`

- Names of the publications on the publisher to subscribe to.

`WITH ( `subscription_parameter` [= `value`] [, ... ] )`

- This clause specifies optional parameters for a subscription.

  The following parameters control what happens during subscription creation:

  `connect` (`boolean`)

- Specifies whether the `CREATE SUBSCRIPTION` command should connect to the publisher at all. The default is `true`. Setting this to `false` will force the values of `create_slot`, `enabled` and `copy_data` to `false`. (You cannot combine setting `connect` to `false` with setting `create_slot`, `enabled`, or `copy_data` to `true`.)

  Since no connection is made when this option is `false`, no tables are subscribed. To initiate replication, you must manually create the replication slot, enable the failover if required, enable the subscription, and refresh the subscription. See logical-replication-subscription-examples-deferred-slot for examples.

`create_slot` (`boolean`)

- Specifies whether the command should create the replication slot on the publisher. The default is `true`.

  If set to `false`, you are responsible for creating the publisher's slot in some other way. See logical-replication-subscription-examples-deferred-slot for examples.

`enabled` (`boolean`)

- Specifies whether the subscription should be actively replicating or whether it should just be set up but not started yet. The default is `true`.

`slot_name` (`string`)

- Name of the publisher's replication slot to use. The default is to use the name of the subscription for the slot name.

  Setting `slot_name` to `NONE` means there will be no replication slot associated with the subscription. Such subscriptions must also have both `enabled` and `create_slot` set to `false`. Use this when you will be creating the replication slot later manually. See logical-replication-subscription-examples-deferred-slot for examples.

  When setting `slot_name` to a valid name and `create_slot` to `false`, the `failover` property value of the named slot may differ from the counterpart `failover` parameter specified in the subscription. Always ensure the slot property `failover` matches the counterpart parameter of the subscription and vice versa. Otherwise, the slot on the publisher may behave differently from what these subscription options say: for example, the slot on the publisher could either be synced to the standbys even when the subscription's `failover` option is disabled or could be disabled for sync even when the subscription's `failover` option is enabled.

The following parameters control the subscription's replication behavior after it has been created:

`binary` (`boolean`)

- Specifies whether the subscription will request the publisher to send the data in binary format (as opposed to text). The default is `false`. Any initial table synchronization copy (see `copy_data`) also uses the same format. Binary format can be faster than the text format, but it is less portable across machine architectures and PostgreSQL versions. Binary format is very data type specific; for example, it will not allow copying from a `smallint` column to an `integer` column, even though that would work fine in text format. Even when this option is enabled, only data types having binary send and receive functions will be transferred in binary. Note that the initial synchronization requires all data types to have binary send and receive functions, otherwise the synchronization will fail (see sql-createtype for more about send/receive functions).

  When doing cross-version replication, it could be that the publisher has a binary send function for some data type, but the subscriber lacks a binary receive function for that type. In such a case, data transfer will fail, and the `binary` option cannot be used.

  If the publisher is a PostgreSQL version before 16, then any initial table synchronization will use text format even if `binary = true`.

`copy_data` (`boolean`)

- Specifies whether to copy pre-existing data in the publications that are being subscribed to when the replication starts. The default is `true`.

  If the publications contain `WHERE` clauses, it will affect what data is copied. Refer to the sql-createsubscription-notes for details.

  See sql-createsubscription-notes for details of how `copy_data = true` can interact with the `origin` parameter.

`streaming` (`enum`)

- Specifies whether to enable streaming of in-progress transactions for this subscription. The default value is `parallel`, meaning incoming changes are directly applied via one of the parallel apply workers, if available. If no parallel apply worker is free to handle streaming transactions then the changes are written to temporary files and applied after the transaction is committed. Note that if an error happens in a parallel apply worker, the finish LSN of the remote transaction might not be reported in the server log.

  There is a risk of deadlock when the schemas of the publisher and subscriber differ, although such cases are rare. The apply worker is equipped to retry these transactions automatically.

  If set to `on`, the incoming changes are written to temporary files and then applied only after the transaction is committed on the publisher and received by the subscriber.

  If set to `off`, all transactions are fully decoded on the publisher and only then sent to the subscriber as a whole.

`synchronous_commit` (`enum`)

- The value of this parameter overrides the guc-synchronous-commit setting within this subscription's apply worker processes. The default value is `off`.

  It is safe to use `off` for logical replication: If the subscriber loses transactions because of missing synchronization, the data will be sent again from the publisher.

  A different setting might be appropriate when doing synchronous logical replication. The logical replication workers report the positions of writes and flushes to the publisher, and when using synchronous replication, the publisher will wait for the actual flush. This means that setting `synchronous_commit` for the subscriber to `off` when the subscription is used for synchronous replication might increase the latency for `COMMIT` on the publisher. In this scenario, it can be advantageous to set `synchronous_commit` to `local` or higher.

`two_phase` (`boolean`)

- Specifies whether two-phase commit is enabled for this subscription. The default is `false`.

  When two-phase commit is enabled, prepared transactions are sent to the subscriber at the time of `PREPARE TRANSACTION`, and are processed as two-phase transactions on the subscriber too. Otherwise, prepared transactions are sent to the subscriber only when committed, and are then processed immediately by the subscriber.

  The implementation of two-phase commit requires that replication has successfully finished the initial table synchronization phase. So even when `two_phase` is enabled for a subscription, the internal two-phase state remains temporarily pending until the initialization phase completes. See column subtwophasestate of pg_subscription to know the actual two-phase state.

`disable_on_error` (`boolean`)

- Specifies whether the subscription should be automatically disabled if any errors are detected by subscription workers during data replication from the publisher. The default is `false`.

`password_required` (`boolean`)

- If set to `true`, connections to the publisher made as a result of this subscription must use password authentication and the password must be specified as a part of the connection string. This setting is ignored when the subscription is owned by a superuser. The default is `true`. Only superusers can set this value to `false`.

`run_as_owner` (`boolean`)

- If true, all replication actions are performed as the subscription owner. If false, replication workers will perform actions on each table as the owner of that table. The latter configuration is generally much more secure; for details, see logical-replication-security. The default is `false`.

`origin` (`string`)

- Specifies whether the subscription will request the publisher to only send changes that don't have an origin or send changes regardless of origin. Setting `origin` to `none` means that the subscription will request the publisher to only send changes that don't have an origin. Setting `origin` to `any` means that the publisher sends changes regardless of their origin. The default is `any`.

  See sql-createsubscription-notes for details of how `copy_data = true` can interact with the `origin` parameter.

`failover` (`boolean`)

- Specifies whether the replication slots associated with the subscription are enabled to be synced to the standbys so that logical replication can be resumed from the new primary after failover. The default is `false`.

When specifying a parameter of type `boolean`, the `=` `value` part can be omitted, which is equivalent to specifying `TRUE`.

## Notes

See logical-replication-security for details on how to configure access control between the subscription and the publication instance.

When creating a replication slot (the default behavior), `CREATE SUBSCRIPTION` cannot be executed inside a transaction block.

Creating a subscription that connects to the same database cluster (for example, to replicate between databases in the same cluster or to replicate within the same database) will only succeed if the replication slot is not created as part of the same command. Otherwise, the `CREATE SUBSCRIPTION` call will hang. To make this work, create the replication slot separately (using the function `pg_create_logical_replication_slot` with the plugin name `pgoutput`) and create the subscription using the parameter `create_slot = false`. See logical-replication-subscription-examples-deferred-slot for examples. This is an implementation restriction that might be lifted in a future release.

If any table in the publication has a `WHERE` clause, rows for which the `expression` evaluates to `false` or `NULL` will not be published. If the subscription has several publications in which the same table has been published with different `WHERE` clauses, a row will be published if any of the expressions (referring to that publish operation) are satisfied. In the case of different `WHERE` clauses, if one of the publications has no `WHERE` clause (referring to that publish operation) or the publication is declared as `FOR ALL TABLES` or `FOR TABLES IN SCHEMA`, rows are always published regardless of the definition of the other expressions. If the subscriber is a PostgreSQL version before 15, then any row filtering is ignored during the initial data synchronization phase. For this case, the user might want to consider deleting any initially copied data that would be incompatible with subsequent filtering. Because initial data synchronization does not take into account the publication `publish` parameter when copying existing table data, some rows may be copied that would not be replicated using DML. See logical-replication-subscription-examples for examples.

Subscriptions having several publications in which the same table has been published with different column lists are not supported.

We allow non-existent publications to be specified so that users can add those later. This means pg_subscription can have non-existent publications.

When using a subscription parameter combination of `copy_data = true` and `origin = NONE`, the initial sync table data is copied directly from the publisher, meaning that knowledge of the true origin of that data is not possible. If the publisher also has subscriptions then the copied table data might have originated from further upstream. This scenario is detected and a WARNING is logged to the user, but the warning is only an indication of a potential problem; it is the user's responsibility to make the necessary checks to ensure the copied data origins are really as wanted or not.

To find which tables might potentially include non-local origins (due to other subscriptions created on the publisher) try this SQL query:

    # substitute <pub-names> below with your publication name(s) to be queried
    SELECT DISTINCT PT.schemaname, PT.tablename
    FROM pg_publication_tables PT
         JOIN pg_class C ON (C.relname = PT.tablename)
         JOIN pg_namespace N ON (N.nspname = PT.schemaname),
         pg_subscription_rel PS
    WHERE C.relnamespace = N.oid AND
          (PS.srrelid = C.oid OR
          C.oid IN (SELECT relid FROM pg_partition_ancestors(PS.srrelid) UNION
                    SELECT relid FROM pg_partition_tree(PS.srrelid))) AND
          PT.pubname IN (<pub-names>);

## Examples

Create a subscription to a remote server that replicates tables in the publications `mypublication` and `insert_only` and starts replicating immediately on commit:

    CREATE SUBSCRIPTION mysub
             CONNECTION 'host=192.168.1.50 port=5432 user=foo dbname=foodb'
            PUBLICATION mypublication, insert_only;

Create a subscription to a remote server that replicates tables in the `insert_only` publication and does not start replicating until enabled at a later time.

    CREATE SUBSCRIPTION mysub
             CONNECTION 'host=192.168.1.50 port=5432 user=foo dbname=foodb'
            PUBLICATION insert_only
                   WITH (enabled = false);

## Compatibility

`CREATE SUBSCRIPTION` is a PostgreSQL extension.

## See Also

- sql-altersubscription
- sql-dropsubscription
- sql-createpublication
- sql-alterpublication