查找一个任务来执行所需要的时间并不依赖于活动任务的个数，而是依赖于优先级的数量。
The time it takes to find a task to execute depends not on the number of active tasks but instead on the number of priorities.
那么就需要对表数据的子集而不是整个表执行维护操作，来减少操作时间，并避免对静态数据进行不必要的操作。
This leads to a requirement for performing maintenance on a subset of table data instead of the entire table in order to reduce operating time and avoid unnecessary operations on static data.
编写系统测试是个挑战，也需要大量的时间来实际地执行。
System tests are challenging to author and also take a good deal of time to actually execute.
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