automatically reduce resolution rather than fail scrape

Signed-off-by: Ziqi Zhao <zhaoziqi9146@gmail.com>

scrape/target.go

@@ -366,13 +366,21 @@ type bucketLimitAppender struct {
 
 func (app *bucketLimitAppender) AppendHistogram(ref storage.SeriesRef, lset labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
 	if h != nil {
-		if len(h.PositiveBuckets)+len(h.NegativeBuckets) > app.limit {
+		for len(h.PositiveBuckets)+len(h.NegativeBuckets) > app.limit {
-			return 0, errBucketLimit
+			lastSum := len(h.PositiveBuckets) + len(h.NegativeBuckets)
+			h = h.ReduceResolution(h.Schema - 1)
+			if len(h.PositiveBuckets)+len(h.NegativeBuckets) == lastSum {
+				return 0, errBucketLimit
+			}
 		}
 	}
 	if fh != nil {
-		if len(fh.PositiveBuckets)+len(fh.NegativeBuckets) > app.limit {
+		for len(fh.PositiveBuckets)+len(fh.NegativeBuckets) > app.limit {
-			return 0, errBucketLimit
+			lastSum := len(fh.PositiveBuckets) + len(fh.NegativeBuckets)
+			fh = fh.ReduceResolution(fh.Schema - 1)
+			if len(fh.PositiveBuckets)+len(fh.NegativeBuckets) == lastSum {
+				return 0, errBucketLimit
+			}
 		}
 	}
 	ref, err := app.Appender.AppendHistogram(ref, lset, t, h, fh)

scrape/target_test.go

@@ -517,6 +517,11 @@ func TestBucketLimitAppender(t *testing.T) {
 			limit:       3,
 			expectError: true,
 		},
+		{
+			h:           example,
+			limit:       4,
+			expectError: false,
+		},
 		{
 			h:           example,
 			limit:       10,