Don't report empty histograms to FastForward #140
Merged
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Rationale
If histograms don't have any reported values, or have not been used
in a long time, the snapshot is empty and the histogram metrics
will not have a reasonable default value. All stats (min, max, median, etc) would
incorrectly be reported as zero
Performance impact
The performance impact should be minimal, since it only adds one additional
if-check when reporting histograms. Snapshot.size() is a fast method, simply
returning the length of its internal array.
For cases where snapshots are empty - i.e. unused histograms we should see
a performance improvement since we can skip emitting the data points to FastForward
as well as skipping the creation of the metric ids.