A representation of the xid event.

Xid event's binlog payload is structured as follow:

Common to both 5.5 and 5.6:
    19 bytes for common v4 event headers
    8 bytes (uint64) for xid.  NOTE: xid is written using the master's
        machine endianness.  The id's value will differ when read on
        different processor platforms; however, replication will function
        correctly since the uniqueness of the id is preserved.
5.6 Specific:
    (optional) 4 bytes footer for checksum