maximum number of tuples 最大元组数
They improve performance by reducing the number of tuples fetched during query execution.
通过减少执行查询时需要检索的元组（tuple）的数量，以及减少查询所需的计算，函数索引能够显著改善性能。
If the number of tuples, calculated by using the Cartesian product, exceeds the set threshold; the NON EMPTY clause is applied to the query.
如果通过使用Cartesian产品计算的元组数超过设定的阈值，将NON empty子句应用于查询。
Usage: This parameter controls the decision on whether or not to apply a NON EMPTY clause on member requests when the number of tuples exceeds the set threshold.
用法：当元组数超过设定的阈值时，该参数控制是否对成员请求应用NON empty子句的决策。
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