Method beginReplication

server/logrepl/replication.go:426–455

beginReplication starts a new replication connection to the primary server and returns it. The LSN provided is the last one we have confirmed that we flushed to disk.

(slotName string, lastFlushLsn pglogrepl.LSN)

// beginReplication starts a new replication connection to the primary server and returns it. The LSN provided is the
// last one we have confirmed that we flushed to disk.
func (r *LogicalReplicator) beginReplication(slotName string, lastFlushLsn pglogrepl.LSN) (*pgconn.PgConn, error) {
	conn, err := pgconn.Connect(context.Background(), r.ReplicationDns())
	if err != nil {
		return nil, err
	}

	// streaming of large transactions is available since PG 14 (protocol version 2)
	// we also need to set 'streaming' to 'true'
	pluginArguments := []string{
		"proto_version '2'",
		fmt.Sprintf("publication_names '%s'", slotName),
		"messages 'true'",
		"streaming 'true'",
	}

	// The LSN is the position in the WAL where we want to start replication, but it can only be used to skip entries,
	// not rewind to previous entries that we've already confirmed to the primary that we flushed. We still pass an LSN
	// for the edge case where we have flushed an entry to disk, but crashed before the primary received confirmation.
	// In that edge case, we want to "skip" entries (from the primary's perspective) that we have already flushed to disk.
	log.Printf("Starting logical replication on slot %s at WAL location %s", slotName, lastFlushLsn+1)
	err = pglogrepl.StartReplication(context.Background(), conn, slotName, lastFlushLsn+1, pglogrepl.StartReplicationOptions{
		PluginArgs: pluginArguments,
	})
	if err != nil {
		return nil, err
	}
	log.Println("Logical replication started on slot", slotName)

	return conn, nil
}

// DropPublication drops the publication with the given name if it exists. Mostly useful for testing.
func DropPublication(primaryDns, slotName string) error {