stats/src/main/java/io/airlift/stats/ExponentialDecay.java
public static double computeAlpha(double targetWeight, long targetAgeInSeconds)
    {
        checkArgument(targetAgeInSeconds > 0, "targetAgeInSeconds must be > 0");
        checkArgument(targetWeight > 0 && targetWeight < 1, "targetWeight must be in range (0, 1)");

        return -Math.log(targetWeight) / targetAgeInSeconds;
    }
public static double computeAlpha(double targetWeight, long targetAgeInSeconds)
    {
        checkArgument(targetAgeInSeconds > 0, "targetAgeInSeconds must be > 0");
        checkArgument(targetWeight > 0 && targetWeight < 1, "targetWeight must be in range (0, 1)");

        return -Math.log(targetWeight) / targetAgeInSeconds;
    }
Compute the alpha decay factor such that the weight of an entry with age 'targetAgeInSeconds' is targetWeight'