ExpHist
Related Docs:
class ExpHist
| package algebird
number of items tracked by this bucket.
timestamp of the most recent item tracked by this bucket.
ExpHist guarantees that the returned guess will be within epsilon relative error of the true count
across a sliding window of size windowSize.
ExpHist guarantees that the returned guess will be within epsilon relative error of the true count
across a sliding window of size windowSize.
relative error, from [0, 0.5]
number of time ticks to track
Value class wrapper around timestamps (>= 0) used by each bucket.
The paper that introduces the exponential histogram proves that, given a positive number l, every
integer s can be uniquely represented as the sum of
The paper that introduces the exponential histogram proves that, given a positive number l, every
integer s can be uniquely represented as the sum of
(l or (l + 1)) * 2i + (# from 1 to (l + 1)) 2j
for i = (0 to j - 1), given some j.
The paper calls this the "l-canonical" representation of s.
It turns out that if you follow the exponential histogram bucket-merging algorithm, you end up with the invariant that the number of buckets with size 2^i exactly matches that power of 2's coefficient in s's l-canonical representation.
Put another way - only sequences of buckets with sizes matching the l-canonical representation of some number s are valid exponential histograms.
(We use this idea in ExpHist.rebucket to take a sequence of buckets of any size and rebucket them into
a sequence where the above invariant holds.)
This is huge. This means that you can implement addAll(newBuckets) by
The resulting sequence of buckets is a valid exponential histogram.
Returns an empty instance with the supplied Config.
Returns an instance directly from a number i.
Returns an instance directly from a number i. All buckets in the returned ExpHist will have the same
timestamp, equal to ts.