You can keep run histories for a specific number of runs or for a specific number of days or months. For example, you can keep the run histories for the ten latest runs (occurrences) or for the past two days or six months. You can also choose to keep all run histories.
You must have read and write permissions for the entry and read or traverse permissions for the folder that contains the entry.
Tip: If you are an administrator, you can also set how long to keep run histories for entries in Cognos Administration from Set properties on the Actions menu next to the entry.
Click the set properties button 
next to the entry you want.
On the General tab, under Run history, choose the retention method and type the value:
To keep run histories for a specific number of occurrences, click Number of occurrences and type the number. To save an unlimited number of run histories, set this value to 0.
To keep run histories for a specific length of time, click Duration and click either Days or Months. Type the appropriate value in the box.
Click OK.
Start Cognos Connection.
In the upper-right corner, click Launch, Cognos Administration.
Click the Status tab, and then click the type of entries you want to view.
Next to the entry, click the arrow and then click Set properties.
On the General tab, under Run history, choose the retention method and type the value:
To keep run histories for a specific number of occurrences, click Number of occurrences and type the number. To save an unlimited number of run histories, set this value to 0.
To keep run histories for a specific length of time, click Duration and click either Days or Months. Type the appropriate value in the box.
Click OK.
