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53.9. Logical Replication Message Formats

This section describes the detailed format of each logical replication message. These messages are returned either by the replication slot SQL interface or are sent by a walsender. In case of a walsender they are encapsulated inside the replication protocol WAL messages as described in Section 53.4 and generally obey same message flow as physical replication.

Begin
Byte1('B')

Identifies the message as a begin message.

Int64

The final LSN of the transaction.

Int64

Commit timestamp of the transaction. The value is in number of microseconds since PostgreSQL epoch (2000-01-01).

Int32

Xid of the transaction.

Message
Byte1('M')

Identifies the message as a logical decoding message.

Int32

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

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.

Commit
Byte1('C')

Identifies the message as a commit message.

Int8

Flags; currently unused (must be 0).

Int64

The LSN of the commit.

Int64

The end LSN of the transaction.

Int64

Commit timestamp of the transaction. The value is in number of microseconds since PostgreSQL epoch (2000-01-01).

Origin
Byte1('O')

Identifies the message as an origin message.

Int64

The LSN of the commit on the origin server.

String

Name of the origin.

Note that there can be multiple Origin messages inside a single transaction.

Relation
Byte1('R')

Identifies the message as a relation message.

Int32

Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.

Int32

ID 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 (except generated columns):

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

ID of the column's data type.

Int32

Type modifier of the column (atttypmod).

Type
Byte1('Y')

Identifies the message as a type message.

Int32

Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.

Int32

ID of the data type.

String

Namespace (empty string for pg_catalog).

String

Name of the data type.

Insert
Byte1('I')

Identifies the message as an insert message.

Int32

Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.

Int32

ID of the relation corresponding to the ID in the relation message.

Byte1('N')

Identifies the following TupleData message as a new tuple.

TupleData

TupleData message part representing the contents of new tuple.

Update
Byte1('U')

Identifies the message as an update message.

Int32

Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.

Int32

ID 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.

Delete
Byte1('D')

Identifies the message as a delete message.

Int32

Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.

Int32

ID of the relation corresponding to the ID in the relation message.

Byte1('K')

Identifies the following TupleData submessage as a key. This field is present if the table in which the delete has happened uses an index as REPLICA IDENTITY.

Byte1('O')

Identifies the following TupleData message as an old tuple. This field is present if the table in which the delete happened has REPLICA IDENTITY set to FULL.

TupleData

TupleData message part representing the contents of the old tuple or primary key, depending on the previous field.

The Delete message may contain either a 'K' message part or an 'O' message part, but never both of them.

Truncate
Byte1('T')

Identifies the message as a truncate message.

Int32

Xid of the transaction (only present for streamed transactions). This field is available since protocol version 2.

Int32

Number of relations

Int8

Option bits for TRUNCATE: 1 for CASCADE, 2 for RESTART IDENTITY

Int32

ID of the relation corresponding to the ID in the relation message. This field is repeated for each relation.

The following messages (Stream Start, Stream Stop, Stream Commit, and Stream Abort) are available since protocol version 2.

Stream Start
Byte1('S')

Identifies the message as a stream start message.

Int32

Xid of the transaction.

Int8

A value of 1 indicates this is the first stream segment for this XID, 0 for any other stream segment.

Stream Stop
Byte1('E')

Identifies the message as a stream stop message.

Stream Commit
Byte1('c')

Identifies the message as a stream commit message.

Int32

Xid of the transaction.

Int8

Flags; currently unused (must be 0).

Int64

The LSN of the commit.

Int64

The end LSN of the transaction.

Int64

Commit timestamp of the transaction. The value is in number of microseconds since PostgreSQL epoch (2000-01-01).

Stream Abort
Byte1('A')

Identifies the message as a stream abort message.

Int32

Xid of the transaction.

Int32

Xid of the subtransaction (will be same as xid of the transaction for top-level transactions).

The following message parts are shared by the above messages.

TupleData
Int16

Number of columns.

Next, one of the following submessages appears for each column (except generated columns):

Byte1('n')

Identifies the data as NULL value.

Or

Byte1('u')

Identifies unchanged TOASTed value (the actual value is not sent).

Or

Byte1('t')

Identifies the data as text formatted value.

Or

Byte1('b')

Identifies the data as binary formatted value.

Int32

Length of the column value.

Byten

The value of the column, either in binary or in text format. (As specified in the preceding format byte). n is the above length.

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