Some embodiments provide a program that queries a database for a subset of a plurality of records in the database. Each record in the plurality of records includes a value for a field. The program further samples the subset of the plurality of records to identify a set of records in the subset of the plurality of records. The program also sorts the set of records based on the value for the field in each record in the set of records. The program further determines a first value for the field of a first record in the sorted set of records and a second value for the field of a second record in the sorted set of records forms a slope that is greater than or equal to a defined slope. The program determines a threshold value for the subset of the plurality of records based on the first record.