When SQL Server creates or updates statistics and a sampling rate is not manually specified, SQL Server calculates a default sampling rate. Depending on the real distribution of data in the underlying table, the default sampling rate may not accurately represent the data distribution and then cause degradation of query plan efficiency.
To improve this scenario, a database administrator can choose to manually update statistics with a specific sampling rate that can better represent the distribution of data. However, a subsequent automatic update statistics operation will reset back to the default sampling rate, possibly reintroducing degradation of query plan efficiency.
With the most recent SQL Server 2016 SP1 CU4, we released an enhancement for the CREATE and UPDATE STATISTICS command – the ability to persist sampling rates between updates with a PERSIST_SAMPLE_PERCENT keyword.
This seems rather useful.