> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/11/the-sql-language/data-types/8.19.-pglsn-xing-bie.md).

# 8.19. pg\_lsn型別

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 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`. 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.


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