Ubuntu Manpage: CREATE_SUBSCRIPTION - define a new subscription

Provided by: postgresql-client-16_16.9-0ubuntu0.24.10.1_amd64

NAME

       CREATE_SUBSCRIPTION - define a new subscription

SYNOPSIS

       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 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 31.2 and Chapter 31.

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
Section 34.1.1.

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 are subscribed. To initiate
replication, you must manually create the replication slot, enable the subscription, and refresh
the subscription. See Section 31.2.3 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 31.2.3 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.

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 31.2.3 for
examples.

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 (CREATE_TYPE(7)) 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 Notes
for details.

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

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 parallel, 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.

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.

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 Section 31.9. 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 Notes for details of how copy_data = true can interact with the origin parameter.

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

NOTES

See Section 31.9 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 31.2.3 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 31.2.2 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.