Message (logical replication)

Logical replication Message format. Identifies the message as a logical decoding message.

Reading PG 18·Select a recorded version

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

Definition PG 18

Byte1('M'): Identifies the message as a logical decoding message.
Int32 (TransactionId): Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.
Int8: Flags; Either 0 for no flags or 1 if the logical decoding message is transactional.
Int64 (XLogRecPtr): The LSN of the logical decoding message.
String: The prefix of the logical decoding message.
Int32: Length of the content.
Byten: The content of the logical decoding message.

Fields in documented order

Position	Format	Meaning
1	Byte1('M')	Identifies the message as a logical decoding message.
2	Int32 (TransactionId)	Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.
3	Int8	Flags; Either 0 for no flags or 1 if the logical decoding message is transactional.
4	Int64 (XLogRecPtr)	The LSN of the logical decoding message.
5	String	The prefix of the logical decoding message.
6	Int32	Length of the content.
7	Byte n	The content of the logical decoding message.

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Complete source facts

fields

map[description:Identifies the message as a logical decoding message. format:Byte1('M')], map[description:Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2. format:Int32 (TransactionId)], map[description:Flags; Either 0 for no flags or 1 if the logical decoding message is transactional. format:Int8], map[description:The LSN of the logical decoding message. format:Int64 (XLogRecPtr)], map[description:The prefix of the logical decoding message. format:String], map[description:Length of the content. format:Int32], map[description:The content of the logical decoding message. format:Byte n]

Source references

Full definition and evidence JSON

Definition sources

center · PostgreSQL 18 · 555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f