Update (logical replication)

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

Reading PG 18·Select a recorded version

Layer: Logical replication payload; distinct from the frontend/backend message envelope
First field: Byte1('U')
manual path: /docs/18/protocol-logicalrep-message-formats.html
signature: Update

Definition PG 18

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.

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.

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Complete source facts

fields

map[description:Identifies the message as an update message. format:Byte1('U')], map[description:Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2. format:Int32 (TransactionId)], map[description:OID of the relation corresponding to the ID in the relation message. format:Int32 (Oid)], map[description: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. format:Byte1('K')], map[description: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. format:Byte1('O')], map[description:TupleData message part representing the contents of the old tuple or primary key. Only present if the previous 'O' or 'K' part is present. format:TupleData], map[description:Identifies the following TupleData message as a new tuple. format:Byte1('N')], map[description:TupleData message part representing the contents of a new tuple. format:TupleData]

Source references

Full definition and evidence JSON

Definition sources

center · PostgreSQL 18 · 555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f