Thepg_lsndata 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 ofXLogRecPtrand an internal system type ofPostgreSQL.
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,16/B374D848. Thepg_lsntype supports the standard comparison operators, like=and>. Two LSNs can be subtracted using the-operator; the result is the number of bytes separating those write-ahead log locations.