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Relation (logical replication)

Logical replication Relation format. Identifies the message as a relation message.

Reading PostgreSQL 18.6.

Description

Logical replication Relation format. Identifies the message as a relation message.

Layer: Logical replication payload; distinct from the frontend/backend message envelope
First field: Byte1('R')

Usage

Relation

Protocol context

This section describes the detailed format of each logical replication message. These messages are either returned by the replication slot SQL interface or are sent by a walsender. In the case of a walsender, they are encapsulated inside replication protocol WAL messages as described in Section 54.4 , and generally obey the same message flow as physical replication. The following messages (Stream Start, Stream Stop, Stream Commit, and Stream Abort) are available since protocol version 2. The following messages (Begin Prepare, Prepare, Commit Prepared, Rollback Prepared, Stream Prepare) are available since protocol version 3. The following message parts are shared by the above messages.

Fields in documented order

Position	Format	Meaning
1	Byte1('R')	Identifies the message as a relation message.
2	Int32 (TransactionId)	Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.
3	Int32 (Oid)	OID of the relation.
4	String	Namespace (empty string for pg_catalog ).
5	String	Relation name.
6	Int8	Replica identity setting for the relation (same as relreplident in pg_class ).
7	Int16	Number of columns.
8	Int8	Flags for the column. Currently can be either 0 for no flags or 1 which marks the column as part of the key.
9	String	Name of the column.
10	Int32 (Oid)	OID of the column's data type.
11	Int32	Type modifier of the column ( atttypmod ).

Manual definition

Byte1('R'): Identifies the message as a relation message.
Int32 (TransactionId): Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.
Int32 (Oid): OID of the relation.
String: Namespace (empty string for pg_catalog).
String: Relation name.
Int8: Replica identity setting for the relation (same as relreplident in pg_class).
Int16: Number of columns.

Next, the following message part appears for each column included in the publication:

Int8: Flags for the column. Currently can be either 0 for no flags or 1 which marks the column as part of the key.
String: Name of the column.
Int32 (Oid): OID of the column's data type.
Int32: Type modifier of the column (atttypmod).

Related entries

Documentation and source

PostgreSQL 18 English manual

Source build

Version: 18.6
Build: https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2
Source fingerprint: 555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f

Compare versions

PostgreSQL 17 → 18: unchanged.

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

Export JSON · Back to Protocol Messages · Recorded in PostgreSQL 10 through 20; the first sample is not necessarily its introduction.