(app|lib)/vmstorage: do not increment vm_rows_ignored_total on NaNs (#7166)

`vm_rows_ignored_total` metric is a metric for users to signalize about
ingestion issues, such as bad timestamp or parsing error.
In commit
a5424e95b3
this metric started to increment each time vmstorage gets NaN. But NaN
is a valid value for Prometheus data model and for Prometheus metrics
exposition format. Exporters from Prometheus ecosystem could expose NaNs
as values for metrics and these values will be delivered to vmstorage
and increment the metric.
Since there is nothing user can do with this, in opposite to parsing
errors or bad timestamps, there is not much sense in incrementing this
metric. So this commit rolls-back `reason="nan_value"` increments.

### Describe Your Changes

Please provide a brief description of the changes you made. Be as
specific as possible to help others understand the purpose and impact of
your modifications.

### Checklist

The following checks are **mandatory**:

- [ ] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).

Signed-off-by: hagen1778 <roman@victoriametrics.com>

(cherry picked from commit 0d4f4b8f7d)
Signed-off-by: hagen1778 <roman@victoriametrics.com>

app/vmstorage/main.go

@@ -451,7 +451,6 @@ func writeStorageMetrics(w io.Writer, strg *storage.Storage) {
 	metrics.WriteCounterUint64(w, `vm_deduplicated_samples_total{type="merge"}`, m.DedupsDuringMerge)
 	metrics.WriteGaugeUint64(w, `vm_snapshots`, m.SnapshotsCount)
 
-	metrics.WriteCounterUint64(w, `vm_rows_ignored_total{reason="nan_value"}`, m.NaNValueRows)
 	metrics.WriteCounterUint64(w, `vm_rows_ignored_total{reason="big_timestamp"}`, m.TooBigTimestampRows)
 	metrics.WriteCounterUint64(w, `vm_rows_ignored_total{reason="small_timestamp"}`, m.TooSmallTimestampRows)
 	metrics.WriteCounterUint64(w, `vm_rows_ignored_total{reason="invalid_raw_metric_name"}`, m.InvalidRawMetricNames)

lib/storage/storage.go

@@ -42,7 +42,6 @@ const (
 type Storage struct {
 	rowsReceivedTotal atomic.Uint64
 	rowsAddedTotal    atomic.Uint64
-	naNValueRows      atomic.Uint64
 
 	tooSmallTimestampRows atomic.Uint64
 	tooBigTimestampRows   atomic.Uint64
@@ -505,7 +504,6 @@ type Metrics struct {
 	DedupsDuringMerge uint64
 	SnapshotsCount    uint64
 
-	NaNValueRows          uint64
 	TooSmallTimestampRows uint64
 	TooBigTimestampRows   uint64
 	InvalidRawMetricNames uint64
@@ -581,7 +579,6 @@ func (s *Storage) UpdateMetrics(m *Metrics) {
 	m.DedupsDuringMerge = dedupsDuringMerge.Load()
 	m.SnapshotsCount += uint64(s.mustGetSnapshotsCount())
 
-	m.NaNValueRows += s.naNValueRows.Load()
 	m.TooSmallTimestampRows += s.tooSmallTimestampRows.Load()
 	m.TooBigTimestampRows += s.tooBigTimestampRows.Load()
 	m.InvalidRawMetricNames += s.invalidRawMetricNames.Load()
@@ -1946,7 +1943,6 @@ func (s *Storage) add(rows []rawRow, dstMrs []*MetricRow, mrs []MetricRow, preci
 			if !decimal.IsStaleNaN(mr.Value) {
 				// Skip NaNs other than Prometheus staleness marker, since the underlying encoding
 				// doesn't know how to work with them.
-				s.naNValueRows.Add(1)
 				continue
 			}
 		}

lib/storage/storage_test.go

@@ -2,7 +2,6 @@ package storage
 
 import (
 	"fmt"
-	"math"
 	"math/rand"
 	"os"
 	"path/filepath"
@@ -1591,9 +1590,6 @@ func TestStorageRowsNotAdded(t *testing.T) {
 		if got, want := gotMetrics.RowsAddedTotal, opts.wantMetrics.RowsAddedTotal; got != want {
 			t.Fatalf("unexpected Metrics.RowsAddedTotal: got %d, want %d", got, want)
 		}
-		if got, want := gotMetrics.NaNValueRows, opts.wantMetrics.NaNValueRows; got != want {
-			t.Fatalf("unexpected Metrics.NaNValueRows: got %d, want %d", got, want)
-		}
 		if got, want := gotMetrics.InvalidRawMetricNames, opts.wantMetrics.InvalidRawMetricNames; got != want {
 			t.Fatalf("unexpected Metrics.InvalidRawMetricNames: got %d, want %d", got, want)
 		}
@@ -1649,22 +1645,6 @@ func TestStorageRowsNotAdded(t *testing.T) {
 		},
 	})
 
-	minTimestamp = time.Now().UnixMilli()
-	maxTimestamp = minTimestamp + 1000
-	mrs = testGenerateMetricRowsForTenant(accountID, projectID, rng, numRows, minTimestamp, maxTimestamp)
-	for i := range numRows {
-		mrs[i].Value = math.NaN()
-	}
-	f(&options{
-		name: "NaN",
-		mrs:  mrs,
-		tr:   TimeRange{minTimestamp, maxTimestamp},
-		wantMetrics: &Metrics{
-			RowsReceivedTotal: numRows,
-			NaNValueRows:      numRows,
-		},
-	})
-
 	minTimestamp = time.Now().UnixMilli()
 	maxTimestamp = minTimestamp + 1000
 	mrs = testGenerateMetricRowsForTenant(accountID, projectID, rng, numRows, minTimestamp, maxTimestamp)