192.1.5 REQUIRED_UNDO_SIZE Function

This function returns the required undo tablespace size (in MB) to satisfy certain undo retention value based on undo statistics available for a given period.

Syntax

Note:

Zero will be returned if the information about the given period is not available.

Viewing the output using the historical information in memory:

DBMS_UNDO_ADV.REQUIRED_UNDO_SIZE(
    retention IN NUMBER)
RETURN NUMBER; 

Viewing the output using start time and end time:

DBMS_UNDO_ADV.REQUIRED_UNDO_SIZE(
    retention  IN NUMBER,
    start_time IN DATE,
    end_time   IN DATE)
RETURN NUMBER;

Viewing the output using begin and end AWR snapshot ID:

DBMS_UNDO_ADV.REQUIRED_UNDO_SIZE(
    retention  IN NUMBER,
    begin_snap IN NUMBER,
    end_snap   IN NUMBER)
RETURN NUMBER;  

Parameters

Table 192-6 REQUIRED_UNDO_SIZE Function Parameters

Parameter	Description
retention	Retention value you want to set for the undo_retention init.ora parameter.
start_time	Start time of the given period.
end_time	End time of the given period.
begin_snap	Begin snapshot identifier. It is based on historical information in AWR from the begin_snap identifier.
end_snap	End snapshot identifier. It is based on historical information in AWR until the end_snap identifier.