如果要执行更复杂的查询，或者要连续执行多个查询，那么执行时间的差距就不是次秒级的，而是以秒甚至分钟来计算的。
If more complex queries are executed, or if several queries are executed in sequence, the difference in the execution time is not just sub-seconds but seconds or even minutes.
如果interval的执行时间较长(比指定的延时长)，那么它们将连续地执行而没有延时。
Intervals may execute back-to-back with no delay if they take long enough to execute (longer than the specified delay).
如果interval的执行时间较长(比指定的延时长)，那么它们将连续地执行而没有延时。
Intervals may execute back-to-back with no delay if they take long enough to execute (longer than the specified delay).
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