Update default exemplar reservoir size for base-2 exponential histogram buckets #3674
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spec:metrics
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Originally posted by @jsuereth in #3670 (comment)
I'd suggest limiting to a range of 5-20 exemplars (or some division of the exponential histogram's max size) purely from an overhead standpoint on tracking these points. I don't have hard numbers to back this up, just some anecdotes.
Here's some VERY lazy math with naive assumptions:
Explicit Bucket histograms
Exponential Bucket Histogram
Given the key size differential, I don't think we should be spending quite as much memory overhead on exemplars. Particularly because Exponential Buckets are intended to give us very high accuracy percentiles. I think we're better of attempting to grab lower number but higher entropy exemplars.
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