[chore] [translator/prometheusremotewrite] ensure unknown reset hint (#…

…29326)

Ensure that native histogram reset hint is UNKNOWN and document
reasoning.

See discussion in the related PR: #28663

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

pkg/translator/prometheusremotewrite/histograms.go

@@ -74,7 +74,17 @@ func exponentialToNativeHistogram(p pmetric.ExponentialHistogramDataPoint) (prom
 	nSpans, nDeltas := convertBucketsLayout(p.Negative(), scaleDown)
 
 	h := prompb.Histogram{
-		Schema: scale,
+		// The counter reset detection must be compatible with Prometheus to
+		// safely set ResetHint to NO. This is not ensured currently.
+		// Sending a sample that triggers counter reset but with ResetHint==NO
+		// would lead to Prometheus panic as it does not double check the hint.
+		// Thus we're explicitly saying UNKNOWN here, which is always safe.
+		// TODO: using created time stamp should be accurate, but we
+		// need to know here if it was used for the detection.
+		// Ref: https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/28663#issuecomment-1810577303
+		// Counter reset detection in Prometheus: https://github.com/prometheus/prometheus/blob/f997c72f294c0f18ca13fa06d51889af04135195/tsdb/chunkenc/histogram.go#L232
+		ResetHint: prompb.Histogram_UNKNOWN,
+		Schema:    scale,
 
 		ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: p.ZeroCount()},
 		// TODO use zero_threshold, if set, see