The Alerts tab of the Console Options window allows you to enter the number of rows you want displayed in the historical Alerts view. While this restriction limits the historical view, there is no limit to the number of rows used for your active alerts. The default entry is 0, which does not limit the number of rows in your historical view.
Access the Console Options window Alerts tab
You can open the Alerts tab of the Console Options window from the SQLDM Console by selecting 
> Console Option, and then selecting the Alerts tab.