Returns the time that SQL Server has been idle since it was last started. The result is in CPU time increments, or "ticks," and is cumulative for all CPUs, so it may exceed the actual elapsed time. Multiply by @@TIMETICKS to convert to microseconds.
If the time returned in @@CPU_BUSY, or @@IO_BUSY exceeds approximately 49 days of cumulative CPU time, you receive an arithmetic overflow warning. In that case, the value of @@CPU_BUSY, @@IO_BUSY and @@IDLE variables are not accurate.
The following example shows returning the number of milliseconds SQL Server was idle between the start time and the current time. To avoid arithmetic overflow when converting the value to microseconds, the example converts one of the values to the float data type.
SELECT @@IDLE * CAST(@@TIMETICKS AS float) AS 'Idle microseconds', GETDATE() AS 'as of'
Here is the result set.
Idle microseconds as of ----------------- ---------------------- 8199934 12/5/2006 10:23:00 AM