pg_lsn data type can be used to store LSN (Log Sequence Number) data which is a pointer to a location in the WAL. This type is a representation of
XLogRecPtr and an internal system type of PostgreSQL.
Internally, an LSN is a 64-bit integer, representing a byte position in the write-ahead log stream. It is printed as two hexadecimal numbers of up to 8 digits each, separated by a slash; for example,
pg_lsn type supports the standard comparison operators, like
>. Two LSNs can be subtracted using the
- operator; the result is the number of bytes separating those write-ahead log locations.