如果采用基于最坏情况下的执行时间(Worst Case Execution Time，WCET)的调度算法，一方面最坏执行时间可能远大于平均执行时间，造成计算资源的浪费[2]；另一方面任务的到达时...
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最后给出测试这两种程序的实验条件和任务，并对这两种程序在不同情况下的执行时间进行分析。
In the end, puts forward the condition and task of the experiment which purpose is to test these two programs and analyzes the executing time under diverse circumstances.
要减少执行时间，除非规则是柱状的，否则，在可能的情况下采用虚拟表，并避免使用抽样。
To reduce execution time, unless the rules are columnar, you should use virtual tables where possible, and avoid using sampling.
避免准备阶段在下面两种情况下最有用：一是sql语句被多次执行；二是准备阶段需要的时间占语句总执行时间的很大一部分。
Avoiding the prepare phase especially pays off if an SQL statement is executed many times and if the prepare phase makes up a significant portion of the statement's overall execution time.
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