8.20. pg_lsn Type
The
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,
16/B374D848
. The
pg_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 locations.