lib/storage: initial support for multi-level downsampling

See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/36

Based on https://github.com/valyala/VictoriaMetrics/pull/203

app/victoria-metrics/main.go

@@ -28,6 +28,8 @@ var (
 		"equal to -dedup.minScrapeInterval > 0. See https://docs.victoriametrics.com/#deduplication and https://docs.victoriametrics.com/#downsampling")
 	dryRun = flag.Bool("dryRun", false, "Whether to check only -promscrape.config and then exit. "+
 		"Unknown config entries are allowed in -promscrape.config by default. This can be changed with -promscrape.config.strictParse")
+	downsamplingPeriods = flagutil.NewArray("downsampling.period", "Comma-separated downsampling periods in the format 'offset:period'. For example, '30d:10m' instructs "+
+		"to leave a single sample per 10 minutes for samples older than 30 days. See https://docs.victoriametrics.com/#downsampling for details")
 )
 
 // custom api help links [["/api","doc"]] without http.pathPrefix.
@@ -57,7 +59,10 @@ func main() {
 
 	logger.Infof("starting VictoriaMetrics at %q...", *httpListenAddr)
 	startTime := time.Now()
-	storage.SetDedupInterval(*minScrapeInterval)
+	err := storage.SetDownsamplingPeriods(*downsamplingPeriods, *minScrapeInterval)
+	if err != nil {
+		logger.Fatalf("cannot parse -downsampling.period: %s", err)
+	}
 	vmstorage.Init(promql.ResetRollupResultCacheIfNeeded)
 	vmselect.Init()
 	vminsert.Init()

app/vmselect/netstorage/netstorage.go

@@ -483,7 +483,7 @@ func (pts *packedTimeseries) Unpack(dst *Result, tbf *tmpBlocksFile, tr storage.
 		dst.Values = append(dst.Values, pts.pd.values...)
 		dst.Timestamps = append(dst.Timestamps, pts.pd.timestamps...)
 	}
-	dedupInterval := storage.GetDedupInterval()
+	dedupInterval := storage.GetDedupInterval(tr.MinTimestamp)
 	mergeSortBlocks(dst, sbs, dedupInterval)
 	if pts.pd != nil {
 		if !sort.IsSorted(dst) {

lib/storage/block.go

@@ -161,7 +161,8 @@ func (b *Block) deduplicateSamplesDuringMerge() {
 		// Nothing to dedup.
 		return
 	}
-	dedupInterval := GetDedupInterval()
+	maxTimestamp := srcTimestamps[len(srcTimestamps)-1]
+	dedupInterval := GetDedupInterval(maxTimestamp)
 	if dedupInterval <= 0 {
 		// Deduplication is disabled.
 		return

lib/storage/dedup.go

@@ -1,27 +1,7 @@
 package storage
 
-import (
-	"time"
-)
-
-// SetDedupInterval sets the deduplication interval, which is applied to raw samples during data ingestion and querying.
-//
-// De-duplication is disabled if dedupInterval is 0.
-//
-// This function must be called before initializing the storage.
-func SetDedupInterval(dedupInterval time.Duration) {
-	globalDedupInterval = dedupInterval.Milliseconds()
-}
-
-// GetDedupInterval returns the dedup interval in milliseconds, which has been set via SetDedupInterval.
-func GetDedupInterval() int64 {
-	return globalDedupInterval
-}
-
-var globalDedupInterval int64
-
 func isDedupEnabled() bool {
-	return globalDedupInterval > 0
+	return len(downsamplingPeriods) > 0
 }
 
 // DeduplicateSamples removes samples from src* if they are closer to each other than dedupInterval in millseconds.

lib/storage/downsampling.go

@@ -0,0 +1,123 @@
+package storage
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
+	"github.com/VictoriaMetrics/metricsql"
+)
+
+// SetDownsamplingPeriods configures downsampling.
+//
+// The function must be called before opening or creating any storage.
+func SetDownsamplingPeriods(periods []string, dedupInterval time.Duration) error {
+	dsps, err := parseDownsamplingPeriods(periods)
+	if err != nil {
+		return err
+	}
+	dedupIntervalMs := dedupInterval.Milliseconds()
+	if dedupIntervalMs > 0 {
+		if len(dsps) > 0 && dsps[len(dsps)-1].Offset == 0 {
+			return fmt.Errorf("-dedup.minScrapeInterval=%s cannot be used if -downsampling.period=%s contains zero offset", dedupInterval, periods)
+		}
+		// Deduplication is a special case of downsampling with zero offset.
+		dsps = append(dsps, DownsamplingPeriod{
+			Offset:   0,
+			Interval: dedupIntervalMs,
+		})
+	}
+	downsamplingPeriods = dsps
+	return nil
+}
+
+// DownsamplingPeriod describes downsampling period
+type DownsamplingPeriod struct {
+	// Offset in milliseconds from the current time when the downsampling with the given interval must be applied
+	Offset int64
+	// Interval for downsampling - only a single sample is left per each interval
+	Interval int64
+}
+
+// String implements interface
+func (dsp DownsamplingPeriod) String() string {
+	offset := time.Duration(dsp.Offset) * time.Millisecond
+	interval := time.Duration(dsp.Interval) * time.Millisecond
+	return fmt.Sprintf("%s:%s", offset, interval)
+}
+
+func (dsp *DownsamplingPeriod) parse(s string) error {
+	idx := strings.Index(s, ":")
+	if idx <= 0 {
+		return fmt.Errorf("incorrect format for downsampling period: %s, want `offset:interval` format", s)
+	}
+	offsetStr, intervalStr := s[:idx], s[idx+1:]
+	interval, err := metricsql.DurationValue(intervalStr, 0)
+	if err != nil {
+		return fmt.Errorf("incorrect interval: %s format for downsampling interval: %s err: %w", intervalStr, s, err)
+	}
+	offset, err := metricsql.DurationValue(offsetStr, 0)
+	if err != nil {
+		return fmt.Errorf("incorrect duration: %s format for downsampling offset: %s err: %w", offsetStr, s, err)
+	}
+	dsp.Interval = interval
+	dsp.Offset = offset
+	// sanity check
+	if offset > 0 && interval > offset {
+		return fmt.Errorf("downsampling interval=%d cannot exceed offset=%d", dsp.Interval, dsp.Offset)
+	}
+	return nil
+}
+
+var downsamplingPeriods []DownsamplingPeriod
+
+// GetDedupInterval returns dedup interval, which must be applied to samples with the given timestamp.
+func GetDedupInterval(timestamp int64) int64 {
+	dsp := getDownsamplingPeriod(timestamp)
+	return dsp.Interval
+}
+
+// getDownsamplingPeriod returns downsampling period, which must be used for the given timestamp
+func getDownsamplingPeriod(timestamp int64) DownsamplingPeriod {
+	offset := int64(fasttime.UnixTimestamp())*1000 - timestamp
+	for _, dsp := range downsamplingPeriods {
+		if offset >= dsp.Offset {
+			return dsp
+		}
+	}
+	return DownsamplingPeriod{}
+}
+
+func parseDownsamplingPeriods(periods []string) ([]DownsamplingPeriod, error) {
+	if len(periods) == 0 {
+		return nil, nil
+	}
+	var dsps []DownsamplingPeriod
+	for _, period := range periods {
+		var dsp DownsamplingPeriod
+		if err := dsp.parse(period); err != nil {
+			return nil, fmt.Errorf("cannot parse downsampling period %q: %w", period, err)
+		}
+		dsps = append(dsps, dsp)
+	}
+	sort.Slice(dsps, func(i, j int) bool {
+		return dsps[i].Offset > dsps[j].Offset
+	})
+	dspPrev := dsps[0]
+	// sanity checks.
+	for _, dsp := range dsps[1:] {
+		if dspPrev.Interval <= dsp.Interval {
+			return nil, fmt.Errorf("prev downsampling interval %d must be bigger than the next interval %d", dspPrev.Interval, dsp.Interval)
+		}
+		if dspPrev.Offset == dsp.Offset {
+			return nil, fmt.Errorf("duplicate downsampling offset: %d", dsp.Offset)
+		}
+		if dspPrev.Interval%dsp.Interval != 0 {
+			return nil, fmt.Errorf("downsamping intervals must be multiples; prev: %d, current: %d", dspPrev.Interval, dsp.Interval)
+		}
+		dspPrev = dsp
+	}
+	return dsps, nil
+}

lib/storage/downsampling_test.go

@@ -0,0 +1,62 @@
+package storage
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestParseDownsamplingPeriodsFailure(t *testing.T) {
+	f := func(name string, src []string) {
+		t.Helper()
+		t.Run(name, func(t *testing.T) {
+			if _, err := parseDownsamplingPeriods(src); err == nil {
+				t.Fatalf("want fail for input: %s", strings.Join(src, ","))
+			}
+		})
+	}
+	f("empty duration", []string{"15d"})
+	f("empty interval", []string{":1m"})
+	f("incorrect duration decrease", []string{"30d:15h", "60d:1h"})
+	f("duplicate offset", []string{"30d:15h", "30d:1h"})
+	f("duplicate interval", []string{"60d:1h", "30d:1h"})
+	f("not multiple intervals", []string{"90d:12h", "60:9h", "30d:7h"})
+}
+
+func TestParseDownsamplingPeriodsSuccess(t *testing.T) {
+	f := func(name string, src []string, expected []DownsamplingPeriod) {
+		t.Helper()
+		t.Run(name, func(t *testing.T) {
+			dsps, err := parseDownsamplingPeriods(src)
+			if err != nil {
+				t.Fatalf("cannot parse downsampling configuration for: %s, err: %s", strings.Join(src, ","), err)
+			}
+			assertDownsamplingPeriods(t, expected, dsps)
+		})
+	}
+	f("one period", []string{"30d:1m"}, []DownsamplingPeriod{
+		{Offset: 30 * 24 * 3600 * 1000, Interval: 60 * 1000},
+	})
+	f("three periods", []string{"15d:30s", "30d:1m", "60d:15m"}, []DownsamplingPeriod{
+		{Offset: 60 * 24 * 3600 * 1000, Interval: 15 * 60 * 1000},
+		{Offset: 30 * 24 * 3600 * 1000, Interval: 60 * 1000},
+		{Offset: 15 * 24 * 3600 * 1000, Interval: 30 * 1000},
+	})
+	f("with the same divider periods", []string{"15d:1m", "30d:7m", "60d:14m", "90d:28m"}, []DownsamplingPeriod{
+		{Offset: 90 * 24 * 3600 * 1000, Interval: 28 * 60 * 1000},
+		{Offset: 60 * 24 * 3600 * 1000, Interval: 14 * 60 * 1000},
+		{Offset: 30 * 24 * 3600 * 1000, Interval: 7 * 60 * 1000},
+		{Offset: 15 * 24 * 3600 * 1000, Interval: 60 * 1000},
+	})
+}
+
+func assertDownsamplingPeriods(t *testing.T, want, got []DownsamplingPeriod) {
+	t.Helper()
+	if len(want) != len(got) {
+		t.Fatalf("len mismatch, want: %d, got: %d", len(want), len(got))
+	}
+	for i := 0; i < len(want); i++ {
+		if want[i] != got[i] {
+			t.Fatalf("want period: %s, got period: %s, idx: %d", want[i], got[i], i)
+		}
+	}
+}

lib/storage/partition.go

@@ -1082,7 +1082,14 @@ func (pt *partition) runFinalDedup() error {
 func isDedupNeeded(pt *partition) bool {
 	pws := pt.GetParts(nil)
 	defer pt.PutParts(pws)
-	dedupInterval := GetDedupInterval()
+	// Get dedup interval, which covers all the parts in the partition.
+	var maxTimestamp int64
+	for _, pw := range pws {
+		if maxTimestamp < pw.p.ph.MaxTimestamp {
+			maxTimestamp = pw.p.ph.MaxTimestamp
+		}
+	}
+	dedupInterval := GetDedupInterval(maxTimestamp)
 	if dedupInterval <= 0 {
 		// The deduplication isn't needed.
 		return false