Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @anurags92, @karlmcguire, and @manishrjain)

cache.go, line 326 at r1 (raw file):

	c.Metrics.updateLatency(hist)

	addToHist := func(key uint64) {

Do we want to still do this even if metrics are disabled? We'll be adding to the map but ultimately discarding the data.

cache.go, line 339 at r1 (raw file):

	onEvict := func(i *Item) {
		if ts, has := startTs[i.Key]; has {
			hist.Update(int64(time.Since(ts) / time.Second))

Add a comment here so it's clearer what the histogram is keeping track of. Like:

// Add the amount of time this item spent in the cache to the histogram.

z/histogram.go, line 83 at r1 (raw file):

}

// PrintHistogram prints the histogram data in a human-readable format.

Update docstring.

Reviewed 1 of 1 files at r2.
Reviewable status: 0 of 2 files reviewed, 3 unresolved discussions (waiting on @anurags92, @karlmcguire, @manishrjain, and @martinmr)