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Update (logical replication)

Logical replication Update format. Identifies the message as an update message.

Reading PostgreSQL 18.6.

Description

Logical replication Update format. Identifies the message as an update message.

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

Usage

Update

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('U')	Identifies the message as an update 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 corresponding to the ID in the relation message.
4	Byte1('K')	Identifies the following TupleData submessage as a key. This field is optional and is only present if the update changed data in any of the column(s) that are part of the REPLICA IDENTITY index.
5	Byte1('O')	Identifies the following TupleData submessage as an old tuple. This field is optional and is only present if table in which the update happened has REPLICA IDENTITY set to FULL.
6	TupleData	TupleData message part representing the contents of the old tuple or primary key. Only present if the previous 'O' or 'K' part is present.
7	Byte1('N')	Identifies the following TupleData message as a new tuple.
8	TupleData	TupleData message part representing the contents of a new tuple.

Manual definition

Byte1('U'): Identifies the message as an update 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 corresponding to the ID in the relation message.
Byte1('K'): Identifies the following TupleData submessage as a key. This field is optional and is only present if the update changed data in any of the column(s) that are part of the REPLICA IDENTITY index.
Byte1('O'): Identifies the following TupleData submessage as an old tuple. This field is optional and is only present if table in which the update happened has REPLICA IDENTITY set to FULL.
TupleData: TupleData message part representing the contents of the old tuple or primary key. Only present if the previous 'O' or 'K' part is present.
Byte1('N'): Identifies the following TupleData message as a new tuple.
TupleData: TupleData message part representing the contents of a new tuple.

The Update message may contain either a 'K' message part or an 'O' message part or neither of them, but never both of them.

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 13 → 14: changed.

--- PostgreSQL 13
+++ PostgreSQL 14
@@ -3,6 +3,10 @@
     {
       "description": "Identifies the message as an update message.",
       "format": "Byte1('U')"
+    },
+    {
+      "description": "Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.",
+      "format": "Int32"
     },
     {
       "description": "ID of the relation corresponding to the ID in the relation message.",

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.