OM2 - CompositeValue + start timestamp + exemplar compliance

[jaydeluca]

• compositeValues:
  • Histogram as single line: foo {count:17,sum:324789.3,bucket:[0.1:8,0.25:10,0.5:11,1.0:14,+Inf:17]} 1.0 st@0.5
  • Summary as single line: bar {count:17,sum:324789.3,quantile:[0.95:123.7,0.99:150.0]}
  • GaugeHistogram as single line with count/sum (not gcount/gsum)
  • _created lines replaced by inline st@ start timestamp
  • _count, _sum, _bucket suffixed lines no longer emitted for these types
  • Reserved label prefix changed from _ to __
  • Histogram/GaugeHistogram Count and Sum always present (MUST, was SHOULD for Sum)
  • Histogram bucket values may be float (SHOULD be integer, was MUST)
  • Spec: CompositeValue, Histogram, Summary
• exemplarCompliance:
  • Exemplar timestamps always emitted (OM2: MUST, was MAY in OM1)
  • 128-char LabelSet hard limit removed