A cost estimation that assumes normal data distribution may not best reflect the real cost of a query when different parameters are used.

假定正常数据分布的开销评估可能并不能最好地反映查询使用不同参数时的实际开销。

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For each predicate in the query, query Tuner adds statistics annotations for the referenced columns in the predicate and also the cost estimation for the predicate.

对于查询中的每个谓词，Query Tuner为谓词中的引用行和谓词的成本评估添加了统计数据注释。

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In the integration server layer, design a query optimizer and research query rewrite, cost estimation model and caches mechanism.

在服务器层设计一个查询优化器，并研究了查询重写和代价估计优化方法以及缓存机制。

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