21 abr 2009

ORA_ROWSCN Pseudocolumn

Después de leer un articulo en OTN "When a table was updated"

Me surge la duda sobre "scn_to_timestamp", en el manual de oracle figura lo siguiente sobre esta función y su seudo columna:

SCN_TO_TIMESTAMP

Purpose

SCN_TO_TIMESTAMP takes as an argument a number that evaluates to a system change number (SCN), and returns the approximate timestamp associated with that SCN. The returned value is of TIMESTAMP datatype. This function is useful any time you want to know the timestamp associated with an SCN. For example, it can be used in conjunction with the ORA_ROWSCN pseudocolumn to associate a timestamp with the most recent change to a row.

ORA_ROWSCN Pseudocolumn

Purpose

For each row, ORA_ROWSCN returns the conservative upper bound system change number (SCN) of the most recent change to the row. This pseudocolumn is useful for determining approximately when a row was last updated. It is not absolutely precise, because Oracle tracks SCNs by transaction committed for the block in which the row resides. You can obtain a more fine-grained approximation of the SCN by creating your tables with row-level dependency tracking. Please refer to CREATE TABLE ... NOROWDEPENDENCIES | ROWDEPENDENCIES for more information on row-level dependency tracking.