Wiki / Protocol Messages / Logical replication formats
Message (logical replication)
Logical replication Message format. Identifies the message as a logical decoding message.
Reading PostgreSQL 18.6.
Description
Logical replication Message format. Identifies the message as a logical decoding message.
- Layer
- Logical replication payload; distinct from the frontend/backend message envelope
- First field
- Byte1('M')
Usage
MessageProtocol 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('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. |
Manual definition
-
- 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.
- Byte
n -
The content of the logical decoding message.
Related entries
Documentation and source
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
Begin (logical replication)Begin Prepare (logical replication)Commit (logical replication)Commit Prepared (logical replication)Delete (logical replication)Insert (logical replication)Origin (logical replication)Prepare (logical replication)Relation (logical replication)Rollback Prepared (logical replication)Stream Abort (logical replication)Stream Commit (logical replication)
Export JSON · Back to Protocol Messages · Recorded in PostgreSQL 14 through 20; the first sample is not necessarily its introduction.