To improve performance, federation frequently USES caching, materialized query tables (MQTs), and distributed query optimization and execution.

要改进性能，联合需要经常使用缓存、物理查询表(MQT)以及分布式查询优化和执行。

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In the distributed query optimization, both local processing cost and transmission cost should be thought over simultaneously.

在分布式查询优化中，应同时考虑本地处理代价和传输代价。

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So most research of distributed query optimization aim at reducing communication cost.

所以大多数研究分布式查询优化以减少通讯开销为目标。

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