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An edit of a task in the Admin Interface will update the taskproperties.xml to the value in <taskruns expiredays="..."/> setting.
Preserving taskrun information
Timeseries without taskruns are referred to as "orphaned timeseries". They can still be viewed in the client and used in calculations but merely the information which workflow was responsible for creating the timeseries has been removed. In order to preserve taskruns longer than the default, the taskruns expirydays property above can be increased, Do this only when necessary. If there are many runs per day, this will make it slower to build up the localDataStore because the taskruns table is bigger.