CREATE SUBSCRIPTION
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## CREATE SUBSCRIPTION

CREATE SUBSCRIPTION — define a new subscription

## Synopsis

    CREATE SUBSCRIPTION subscription_name
        { SERVER server_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 Section 29.2 and Chapter 29.

## Parameters

`subscription_name` #

  The name of the new subscription.

`SERVER `server_name`` #

  A foreign server to use for the connection. The server's foreign data wrapper must have a `connection_function` registered, and a user mapping for the subscription owner on the server must exist. Additionally, the subscription owner must have `USAGE` privileges on `server_name`.

`CONNECTION '`conninfo`'` #

  The libpq connection string defining how to connect to the publisher database. For details see Section 32.1.1.

`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 and sequences 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 Section 29.2.3 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 Section 29.2.3 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. The name cannot be `pg_conflict_detection` as it is reserved for the conflict detection.

    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 Section 29.2.3 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 CREATE TYPE for more about send/receive functions). This parameter has no effect for sequences.

    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 Notes for details.

    See Notes for details of how `copy_data = true` can interact with the `origin` parameter.

    See Section 29.7.1 for recommendations on how to handle any warnings about sequence definition differences between the publisher and the subscriber, which might occur when `copy_data = true`.

  `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. This parameter has no effect for sequences.

    ### Caution

    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 synchronous_commit setting within this subscription's apply worker processes. The default value is `off`. This parameter has no effect for sequences.

    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`. This parameter has no effect for sequences.

    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 or sequence as the owner of that relation. The latter configuration is generally much more secure; for details, see Section 29.12. 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`. This parameter has no effect for sequences.

    See 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`.

  `retain_dead_tuples` (`boolean`) #

    Specifies whether the information (e.g., dead tuples, commit timestamps, and origins) required for conflict detection on the subscriber is retained. The default is `false`. If set to `true`, the detection of update_deleted is enabled, and a physical replication slot named “`pg_conflict_detection`” is created on the subscriber to prevent the information for detecting conflicts from being removed. This parameter has no effect for sequences.

    Note that the information useful for conflict detection is retained only after the creation of the slot. You can verify the existence of this slot by querying pg_replication_slots. And even if multiple subscriptions on one node enable this option, only one replication slot will be created. Also, `wal_level` must be set to `replica` or higher to allow the replication slot to be used.

    ### Caution

    Note that the information for conflict detection cannot be purged if the subscription is disabled; thus, the information will accumulate until the subscription is enabled. To prevent excessive accumulation, it is recommended to disable `retain_dead_tuples` if the subscription will be inactive for an extended period.

    Additionally when enabling `retain_dead_tuples` for conflict detection in logical replication, it is important to design the replication topology to balance data retention requirements with overall system performance. This option provides minimal performance overhead when applied appropriately. The following scenarios illustrate effective usage patterns when enabling this option.

    a. Large Tables with Bidirectional Writes: For large tables subject to concurrent writes on both publisher and subscriber nodes, publishers can define row filters when creating publications to segment data. This allows multiple subscriptions to replicate exclusive subsets of the table in parallel, optimizing the throughput.

    b. Write-Enabled Subscribers: If a subscriber node is expected to perform write operations, replication can be structured using multiple publications and subscriptions. By distributing tables across these publications, the workload is spread among several apply workers, improving concurrency and reducing contention.

    c. Read-Only Subscribers: In configurations involving single or multiple publisher nodes performing concurrent write operations, read-only subscriber nodes may replicate changes without seeing a performance impact if it does index scan. However, if the subscriber is impacted due to replication lag or scan performance (say due to sequential scans), it needs to follow one of the two previous strategies to distribute the workload on the subscriber.

    This option cannot be enabled if the publisher is a physical standby.

    Enabling this option ensures retention of information useful for conflict detection solely for changes occurring locally on the publisher. For the changes originating from different origins, reliable conflict detection cannot be guaranteed.

  `max_retention_duration` (`integer`) #

    Maximum duration in milliseconds for which this subscription's apply worker is allowed to retain the information useful for conflict detection when `retain_dead_tuples` is enabled. The default value is `0`, indicating that the information is retained until it is no longer needed for detection purposes.

    The information useful for conflict detection is no longer retained if all apply workers associated with the subscriptions, where `retain_dead_tuples` is enabled, confirm that the retention duration has exceeded the `max_retention_duration` set within the corresponding subscription. The retention will automatically resume when at least one apply worker confirms that the retention duration is within the specified limit, or when a new subscription is created with `retain_dead_tuples = true`. Alternatively, retention can be manually resumed by re-enabling `retain_dead_tuples`.

    Note that overall retention will not stop if other subscriptions that have a value greater than 0 for this parameter have not exceeded it, or if they set this option to 0.

    This option is effective only when `retain_dead_tuples` is enabled and the apply worker associated with the subscription is active.

    ### Warning

    Note that setting a non-zero value for this option could lead to information for conflict detection being removed prematurely, potentially resulting in incorrect conflict detection.

  `wal_receiver_timeout` (`text`) #

    The value of this parameter overrides the wal_receiver_timeout setting within this subscription's apply worker processes. The default value is `-1`, which means it does not override the global setting, i.e., the value from the server configuration, command line, role or database settings will be used instead.

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

## Notes

See Section 29.12 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 Section 29.2.3 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 Section 29.2.2 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

ALTER SUBSCRIPTION, DROP SUBSCRIPTION, CREATE PUBLICATION, ALTER PUBLICATION

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