8.19.pg_lsn Type

Thepg_lsn data type can be used to store LSN (Log Sequence Number) data which is a pointer to a location in the XLOG. This type is a representation ofXLogRecPtr and 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_lsn type 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 positions.