app/vmselect/graphite: add /tags/findSeries handler from Graphite Tags API

See https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags

README.md

@@ -207,6 +207,7 @@ or [an alternative dashboard for VictoriaMetrics cluster](https://grafana.com/gr
       - `metrics/index.json` - returns all the metric names. See [these docs](https://graphite-api.readthedocs.io/en/latest/api.html#metrics-index-json).
       - `tags` - returns tag names. See [these docs](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags).
       - `tags/<tag_name>` - returns tag values for the given `<tag_name>`. See [these docs](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags).
+      - `tags/findSeries` - returns series matching the given `expr`. See [these docs](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags).
 
 * URL for time series deletion: `http://<vmselect>:8481/delete/<accountID>/prometheus/api/v1/admin/tsdb/delete_series?match[]=<timeseries_selector_for_delete>`.
   Note that the `delete_series` handler should be used only in exceptional cases such as deletion of accidentally ingested incorrect time series. It shouldn't

app/vmselect/graphite/tags_api.go

@@ -3,16 +3,98 @@ package graphite
 import (
 	"fmt"
 	"net/http"
+	"sort"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/bufferedwriter"
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/netstorage"
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/searchutils"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/auth"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
 	"github.com/VictoriaMetrics/metrics"
 )
 
+// TagsFindSeriesHandler implements /tags/findSeries endpoint from Graphite Tags API.
+//
+// See https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags
+func TagsFindSeriesHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter, r *http.Request) error {
+	deadline := searchutils.GetDeadlineForQuery(r, startTime)
+	if err := r.ParseForm(); err != nil {
+		return fmt.Errorf("cannot parse form values: %w", err)
+	}
+	limit, err := getInt(r, "limit")
+	if err != nil {
+		return err
+	}
+	exprs := r.Form["expr"]
+	if len(exprs) == 0 {
+		return fmt.Errorf("expecting at least one `expr` query arg")
+	}
+
+	// Convert exprs to []storage.TagFilter
+	tfs := make([]storage.TagFilter, 0, len(exprs))
+	for _, expr := range exprs {
+		tf, err := parseFilterExpr(expr)
+		if err != nil {
+			return fmt.Errorf("cannot parse `expr` query arg: %w", err)
+		}
+		tfs = append(tfs, *tf)
+	}
+
+	// Send the request to storage
+	ct := time.Now().UnixNano() / 1e6
+	sq := &storage.SearchQuery{
+		MinTimestamp: 0,
+		MaxTimestamp: ct,
+		TagFilterss:  [][]storage.TagFilter{tfs},
+	}
+	denyPartialResponse := searchutils.GetDenyPartialResponse(r)
+	mns, isPartial, err := netstorage.SearchMetricNames(at, denyPartialResponse, sq, deadline)
+	if err != nil {
+		return fmt.Errorf("cannot fetch metric names for %q: %w", sq, err)
+	}
+	paths := getCanonicalPaths(mns)
+	if limit > 0 && limit < len(paths) {
+		paths = paths[:limit]
+	}
+
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	bw := bufferedwriter.Get(w)
+	defer bufferedwriter.Put(bw)
+	WriteTagsFindSeriesResponse(bw, isPartial, paths)
+	if err := bw.Flush(); err != nil {
+		return err
+	}
+	tagsFindSeriesDuration.UpdateDuration(startTime)
+	return nil
+}
+
+func getCanonicalPaths(mns []storage.MetricName) []string {
+	paths := make([]string, 0, len(mns))
+	var b []byte
+	var tags []storage.Tag
+	for _, mn := range mns {
+		b = append(b[:0], mn.MetricGroup...)
+		tags = append(tags[:0], mn.Tags...)
+		sort.Slice(tags, func(i, j int) bool {
+			return string(tags[i].Key) < string(tags[j].Key)
+		})
+		for _, tag := range tags {
+			b = append(b, ';')
+			b = append(b, tag.Key...)
+			b = append(b, '=')
+			b = append(b, tag.Value...)
+		}
+		paths = append(paths, string(b))
+	}
+	sort.Strings(paths)
+	return paths
+}
+
+var tagsFindSeriesDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/tags/findSeries"}`)
+
 // TagValuesHandler implements /tags/<tag_name> endpoint from Graphite Tags API.
 //
 // See https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags
@@ -88,3 +170,31 @@ func getInt(r *http.Request, argName string) (int, error) {
 	}
 	return n, nil
 }
+
+func parseFilterExpr(s string) (*storage.TagFilter, error) {
+	n := strings.Index(s, "=")
+	if n < 0 {
+		return nil, fmt.Errorf("missing tag value in filter expression %q", s)
+	}
+	tagName := s[:n]
+	tagValue := s[n+1:]
+	isNegative := false
+	if strings.HasSuffix(tagName, "!") {
+		isNegative = true
+		tagName = tagName[:len(tagName)-1]
+	}
+	if tagName == "name" {
+		tagName = ""
+	}
+	isRegexp := false
+	if strings.HasPrefix(tagValue, "~") {
+		isRegexp = true
+		tagValue = "^(?:" + tagValue[1:] + ").*"
+	}
+	return &storage.TagFilter{
+		Key:        []byte(tagName),
+		Value:      []byte(tagValue),
+		IsNegative: isNegative,
+		IsRegexp:   isRegexp,
+	}, nil
+}

app/vmselect/graphite/tags_find_series_response.qtpl

@@ -0,0 +1,12 @@
+{% stripspace %}
+
+{% func TagsFindSeriesResponse(isPartial bool, paths []string) %}
+[
+	{% for i, path := range paths %}
+		{%q= path %}
+		{% if i+1 < len(paths) %},{% endif %}
+	{% endfor %}
+]
+{% endfunc %}
+
+{% endstripspace %}

app/vmselect/graphite/tags_find_series_response.qtpl.go

@@ -0,0 +1,65 @@
+// Code generated by qtc from "tags_find_series_response.qtpl". DO NOT EDIT.
+// See https://github.com/valyala/quicktemplate for details.
+
+//line app/vmselect/graphite/tags_find_series_response.qtpl:3
+package graphite
+
+//line app/vmselect/graphite/tags_find_series_response.qtpl:3
+import (
+	qtio422016 "io"
+
+	qt422016 "github.com/valyala/quicktemplate"
+)
+
+//line app/vmselect/graphite/tags_find_series_response.qtpl:3
+var (
+	_ = qtio422016.Copy
+	_ = qt422016.AcquireByteBuffer
+)
+
+//line app/vmselect/graphite/tags_find_series_response.qtpl:3
+func StreamTagsFindSeriesResponse(qw422016 *qt422016.Writer, isPartial bool, paths []string) {
+//line app/vmselect/graphite/tags_find_series_response.qtpl:3
+	qw422016.N().S(`[`)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:5
+	for i, path := range paths {
+//line app/vmselect/graphite/tags_find_series_response.qtpl:6
+		qw422016.N().Q(path)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:7
+		if i+1 < len(paths) {
+//line app/vmselect/graphite/tags_find_series_response.qtpl:7
+			qw422016.N().S(`,`)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:7
+		}
+//line app/vmselect/graphite/tags_find_series_response.qtpl:8
+	}
+//line app/vmselect/graphite/tags_find_series_response.qtpl:8
+	qw422016.N().S(`]`)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+}
+
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+func WriteTagsFindSeriesResponse(qq422016 qtio422016.Writer, isPartial bool, paths []string) {
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	qw422016 := qt422016.AcquireWriter(qq422016)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	StreamTagsFindSeriesResponse(qw422016, isPartial, paths)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	qt422016.ReleaseWriter(qw422016)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+}
+
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+func TagsFindSeriesResponse(isPartial bool, paths []string) string {
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	qb422016 := qt422016.AcquireByteBuffer()
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	WriteTagsFindSeriesResponse(qb422016, isPartial, paths)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	qs422016 := string(qb422016.B)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	qt422016.ReleaseByteBuffer(qb422016)
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+	return qs422016
+//line app/vmselect/graphite/tags_find_series_response.qtpl:10
+}

app/vmselect/main.go

@@ -209,7 +209,7 @@ func selectHandler(startTime time.Time, w http.ResponseWriter, r *http.Request,
 			return true
 		}
 	}
-	if strings.HasPrefix(p.Suffix, "graphite/tags/") {
+	if strings.HasPrefix(p.Suffix, "graphite/tags/") && p.Suffix != "graphite/tags/findSeries" {
 		tagName := p.Suffix[len("graphite/tags/"):]
 		graphiteTagValuesRequests.Inc()
 		if err := graphite.TagValuesHandler(startTime, at, tagName, w, r); err != nil {
@@ -354,6 +354,14 @@ func selectHandler(startTime time.Time, w http.ResponseWriter, r *http.Request,
 			return true
 		}
 		return true
+	case "graphite/tags/findSeries":
+		graphiteTagsFindSeriesRequests.Inc()
+		if err := graphite.TagsFindSeriesHandler(startTime, at, w, r); err != nil {
+			graphiteTagsFindSeriesErrors.Inc()
+			httpserver.Errorf(w, r, "error in %q: %s", r.URL.Path, err)
+			return true
+		}
+		return true
 	case "prometheus/api/v1/rules":
 		// Return dumb placeholder
 		rulesRequests.Inc()
@@ -463,6 +471,9 @@ var (
 	graphiteTagValuesRequests = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/graphite/tags/<tag_name>"}`)
 	graphiteTagValuesErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/select/{}/graphite/tags/<tag_name>"}`)
 
+	graphiteTagsFindSeriesRequests = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/graphite/tags/findSeries"}`)
+	graphiteTagsFindSeriesErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/select/{}/graphite/tags/findSeries"}`)
+
 	rulesRequests    = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/rules"}`)
 	alertsRequests   = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/alerts"}`)
 	metadataRequests = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/metadata"}`)

app/vmselect/netstorage/netstorage.go

@@ -1151,7 +1151,6 @@ func GetSeriesCount(at *auth.Token, denyPartialResponse bool, deadline searchuti
 		}
 		isPartial = true
 	}
-
 	return n, isPartial, nil
 }
 
@@ -1237,6 +1236,81 @@ func ExportBlocks(at *auth.Token, sq *storage.SearchQuery, deadline searchutils.
 	return nil
 }
 
+// SearchMetricNames returns all the metric names matching sq until the given deadline.
+func SearchMetricNames(at *auth.Token, denyPartialResponse bool, sq *storage.SearchQuery, deadline searchutils.Deadline) ([]storage.MetricName, bool, error) {
+	if deadline.Exceeded() {
+		return nil, false, fmt.Errorf("timeout exceeded before starting to search metric names: %s", deadline.String())
+	}
+	requestData := sq.Marshal(nil)
+
+	// Send the query to all the storage nodes in parallel.
+	type nodeResult struct {
+		metricNames [][]byte
+		err         error
+	}
+	resultsCh := make(chan nodeResult, len(storageNodes))
+	for _, sn := range storageNodes {
+		go func(sn *storageNode) {
+			sn.searchMetricNamesRequests.Inc()
+			metricNames, err := sn.processSearchMetricNames(requestData, deadline)
+			if err != nil {
+				sn.searchMetricNamesRequestErrors.Inc()
+				err = fmt.Errorf("cannot search metric names on vmstorage %s: %w", sn.connPool.Addr(), err)
+			}
+			resultsCh <- nodeResult{
+				metricNames: metricNames,
+				err:         err,
+			}
+		}(sn)
+	}
+
+	// Collect results.
+	var errors []error
+	metricNames := make(map[string]struct{})
+	for i := 0; i < len(storageNodes); i++ {
+		// There is no need in timer here, since all the goroutines executing
+		// sn.processSearchQuery must be finished until the deadline.
+		nr := <-resultsCh
+		if nr.err != nil {
+			errors = append(errors, nr.err)
+			continue
+		}
+		for _, metricName := range nr.metricNames {
+			metricNames[string(metricName)] = struct{}{}
+		}
+	}
+	isPartial := false
+	if len(errors) > 0 {
+		if len(errors) == len(storageNodes) {
+			// Return only the first error, since it has no sense in returning all errors.
+			return nil, false, errors[0]
+		}
+
+		// Just return partial results.
+		// This allows gracefully degrade vmselect in the case
+		// if certain storageNodes are temporarily unavailable.
+		// Do not return the error, since it may spam logs on busy vmselect
+		// serving high amounts of requests.
+		partialSearchResults.Inc()
+		if denyPartialResponse {
+			return nil, true, errors[0]
+		}
+		isPartial = true
+	}
+
+	// Unmarshal metricNames
+	mns := make([]storage.MetricName, len(metricNames))
+	i := 0
+	for metricName := range metricNames {
+		mn := &mns[i]
+		if err := mn.Unmarshal(bytesutil.ToUnsafeBytes(metricName)); err != nil {
+			return nil, false, fmt.Errorf("cannot unmarshal metric name obtained from vmstorage: %w; metricName=%q", err, metricName)
+		}
+		i++
+	}
+	return mns, isPartial, nil
+}
+
 // ProcessSearchQuery performs sq until the given deadline.
 //
 // Results.RunParallel or Results.Cancel must be called on the returned Results.
@@ -1399,9 +1473,15 @@ type storageNode struct {
 	// The number of errors during requests to seriesCount.
 	seriesCountRequestErrors *metrics.Counter
 
+	// The number of 'search metric names' requests to storageNode.
+	searchMetricNamesRequests *metrics.Counter
+
 	// The number of search requests to storageNode.
 	searchRequests *metrics.Counter
 
+	// The number of 'search metric names' errors to storageNode.
+	searchMetricNamesRequestErrors *metrics.Counter
+
 	// The number of search request errors to storageNode.
 	searchRequestErrors *metrics.Counter
 
@@ -1593,6 +1673,25 @@ func (sn *storageNode) getSeriesCount(accountID, projectID uint32, deadline sear
 	return n, nil
 }
 
+func (sn *storageNode) processSearchMetricNames(requestData []byte, deadline searchutils.Deadline) ([][]byte, error) {
+	var metricNames [][]byte
+	f := func(bc *handshake.BufferedConn) error {
+		mns, err := sn.processSearchMetricNamesOnConn(bc, requestData)
+		if err != nil {
+			return err
+		}
+		metricNames = mns
+		return nil
+	}
+	if err := sn.execOnConn("searchMetricNames_v1", f, deadline); err != nil {
+		// Try again before giving up.
+		if err = sn.execOnConn("searchMetricNames_v1", f, deadline); err != nil {
+			return nil, err
+		}
+	}
+	return metricNames, nil
+}
+
 func (sn *storageNode) processSearchQuery(requestData []byte, fetchData bool, processBlock func(mb *storage.MetricBlock) error, deadline searchutils.Deadline) error {
 	var blocksRead int
 	f := func(bc *handshake.BufferedConn) error {
@@ -2078,6 +2177,42 @@ const maxMetricBlockSize = 1024 * 1024
 // from vmstorage.
 const maxErrorMessageSize = 64 * 1024
 
+func (sn *storageNode) processSearchMetricNamesOnConn(bc *handshake.BufferedConn, requestData []byte) ([][]byte, error) {
+	// Send the requst to sn.
+	if err := writeBytes(bc, requestData); err != nil {
+		return nil, fmt.Errorf("cannot write requestData: %w", err)
+	}
+	if err := bc.Flush(); err != nil {
+		return nil, fmt.Errorf("cannot flush requestData to conn: %w", err)
+	}
+
+	// Read response error.
+	buf, err := readBytes(nil, bc, maxErrorMessageSize)
+	if err != nil {
+		return nil, fmt.Errorf("cannot read error message: %w", err)
+	}
+	if len(buf) > 0 {
+		return nil, newErrRemote(buf)
+	}
+
+	// Read metricNames from response.
+	metricNamesCount, err := readUint64(bc)
+	if err != nil {
+		return nil, fmt.Errorf("cannot read metricNamesCount: %w", err)
+	}
+	metricNames := make([][]byte, 0, metricNamesCount)
+	for i := int64(0); i < int64(metricNamesCount); i++ {
+		buf, err = readBytes(buf[:0], bc, maxMetricNameSize)
+		if err != nil {
+			return nil, fmt.Errorf("cannot read metricName #%d: %w", i+1, err)
+		}
+		metricNames[i] = append(metricNames[i][:0], buf...)
+	}
+	return metricNames, nil
+}
+
+const maxMetricNameSize = 64 * 1024
+
 func (sn *storageNode) processSearchQueryOnConn(bc *handshake.BufferedConn, requestData []byte, fetchData bool, processBlock func(mb *storage.MetricBlock) error) (int, error) {
 	// Send the request to sn.
 	if err := writeBytes(bc, requestData); err != nil {
@@ -2090,11 +2225,8 @@ func (sn *storageNode) processSearchQueryOnConn(bc *handshake.BufferedConn, requ
 		return 0, fmt.Errorf("cannot flush requestData to conn: %w", err)
 	}
 
-	var err error
-	var buf []byte
-
 	// Read response error.
-	buf, err = readBytes(buf[:0], bc, maxErrorMessageSize)
+	buf, err := readBytes(nil, bc, maxErrorMessageSize)
 	if err != nil {
 		return 0, fmt.Errorf("cannot read error message: %w", err)
 	}
@@ -2248,7 +2380,9 @@ func InitStorageNodes(addrs []string) {
 			tsdbStatusRequestErrors:             metrics.NewCounter(fmt.Sprintf(`vm_request_errors_total{action="tsdbStatus", type="rpcClient", name="vmselect", addr=%q}`, addr)),
 			seriesCountRequests:                 metrics.NewCounter(fmt.Sprintf(`vm_requests_total{action="seriesCount", type="rpcClient", name="vmselect", addr=%q}`, addr)),
 			seriesCountRequestErrors:            metrics.NewCounter(fmt.Sprintf(`vm_request_errors_total{action="seriesCount", type="rpcClient", name="vmselect", addr=%q}`, addr)),
+			searchMetricNamesRequests:           metrics.NewCounter(fmt.Sprintf(`vm_requests_total{action="searchMetricNames", type="rpcClient", name="vmselect", addr=%q}`, addr)),
 			searchRequests:                      metrics.NewCounter(fmt.Sprintf(`vm_requests_total{action="search", type="rpcClient", name="vmselect", addr=%q}`, addr)),
+			searchMetricNamesRequestErrors:      metrics.NewCounter(fmt.Sprintf(`vm_request_errors_total{action="searchMetricNames", type="rpcClient", name="vmselect", addr=%q}`, addr)),
 			searchRequestErrors:                 metrics.NewCounter(fmt.Sprintf(`vm_request_errors_total{action="search", type="rpcClient", name="vmselect", addr=%q}`, addr)),
 			metricBlocksRead:                    metrics.NewCounter(fmt.Sprintf(`vm_metric_blocks_read_total{name="vmselect", addr=%q}`, addr)),
 			metricRowsRead:                      metrics.NewCounter(fmt.Sprintf(`vm_metric_rows_read_total{name="vmselect", addr=%q}`, addr)),

app/vmselect/prometheus/prometheus.go

@@ -952,6 +952,34 @@ func SeriesHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter, r
 		TagFilterss:  tagFilterss,
 	}
 	denyPartialResponse := searchutils.GetDenyPartialResponse(r)
+	if end-start > 24*3600*1000 {
+		// It is cheaper to call SearchMetricNames on time ranges exceeding a day.
+		mns, isPartial, err := netstorage.SearchMetricNames(at, denyPartialResponse, sq, deadline)
+		if err != nil {
+			return fmt.Errorf("cannot fetch time series for %q: %w", sq, err)
+		}
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		bw := bufferedwriter.Get(w)
+		defer bufferedwriter.Put(bw)
+		resultsCh := make(chan *quicktemplate.ByteBuffer)
+		doneCh := make(chan struct{})
+		go func() {
+			for i := range mns {
+				bb := quicktemplate.AcquireByteBuffer()
+				writemetricNameObject(bb, &mns[i])
+				resultsCh <- bb
+			}
+			close(doneCh)
+		}()
+		// WriteSeriesResponse must consume all the data from resultsCh.
+		WriteSeriesResponse(bw, isPartial, resultsCh)
+		if err := bw.Flush(); err != nil {
+			return err
+		}
+		<-doneCh
+		seriesDuration.UpdateDuration(startTime)
+		return nil
+	}
 	rss, isPartial, err := netstorage.ProcessSearchQuery(at, denyPartialResponse, sq, false, deadline)
 	if err != nil {
 		return fmt.Errorf("cannot fetch data for %q: %w", sq, err)

app/vmstorage/transport/server.go

@@ -538,6 +538,20 @@ func (ctx *vmselectRequestCtx) readAccountIDProjectID() (uint32, uint32, error)
 	return accountID, projectID, nil
 }
 
+func (ctx *vmselectRequestCtx) readSearchQuery() error {
+	if err := ctx.readDataBufBytes(maxSearchQuerySize); err != nil {
+		return fmt.Errorf("cannot read searchQuery: %w", err)
+	}
+	tail, err := ctx.sq.Unmarshal(ctx.dataBuf)
+	if err != nil {
+		return fmt.Errorf("cannot unmarshal SearchQuery: %w", err)
+	}
+	if len(tail) > 0 {
+		return fmt.Errorf("unexpected non-zero tail left after unmarshaling SearchQuery: (len=%d) %q", len(tail), tail)
+	}
+	return nil
+}
+
 func (ctx *vmselectRequestCtx) readDataBufBytes(maxDataSize int) error {
 	ctx.sizeBuf = bytesutil.Resize(ctx.sizeBuf, 8)
 	if _, err := io.ReadFull(ctx.bc, ctx.sizeBuf); err != nil {
@@ -663,7 +677,9 @@ func (s *Server) processVMSelectRequest(ctx *vmselectRequestCtx) error {
 
 	switch rpcName {
 	case "search_v4":
-		return s.processVMSelectSearchQuery(ctx)
+		return s.processVMSelectSearch(ctx)
+	case "searchMetricNames_v1":
+		return s.processVMSelectSearchMetricNames(ctx)
 	case "labelValuesOnTimeRange_v1":
 		return s.processVMSelectLabelValuesOnTimeRange(ctx)
 	case "labelValues_v2":
@@ -1061,19 +1077,52 @@ func writeTopHeapEntries(ctx *vmselectRequestCtx, a []storage.TopHeapEntry) erro
 // maxSearchQuerySize is the maximum size of SearchQuery packet in bytes.
 const maxSearchQuerySize = 1024 * 1024
 
-func (s *Server) processVMSelectSearchQuery(ctx *vmselectRequestCtx) error {
-	vmselectSearchQueryRequests.Inc()
+func (s *Server) processVMSelectSearchMetricNames(ctx *vmselectRequestCtx) error {
+	vmselectSearchMetricNamesRequests.Inc()
 
-	// Read search query.
-	if err := ctx.readDataBufBytes(maxSearchQuerySize); err != nil {
-		return fmt.Errorf("cannot read searchQuery: %w", err)
+	// Read request.
+	if err := ctx.readSearchQuery(); err != nil {
+		return err
 	}
-	tail, err := ctx.sq.Unmarshal(ctx.dataBuf)
+
+	// Search metric names.
+	if err := ctx.setupTfss(); err != nil {
+		return ctx.writeErrorMessage(err)
+	}
+	tr := storage.TimeRange{
+		MinTimestamp: ctx.sq.MinTimestamp,
+		MaxTimestamp: ctx.sq.MaxTimestamp,
+	}
+	mns, err := s.storage.SearchMetricNames(ctx.sq.AccountID, ctx.sq.ProjectID, ctx.tfss, tr, *maxMetricsPerSearch, ctx.deadline)
 	if err != nil {
-		return fmt.Errorf("cannot unmarshal SearchQuery: %w", err)
+		return ctx.writeErrorMessage(err)
 	}
-	if len(tail) > 0 {
-		return fmt.Errorf("unexpected non-zero tail left after unmarshaling SearchQuery: (len=%d) %q", len(tail), tail)
+
+	// Send empty error message to vmselect.
+	if err := ctx.writeString(""); err != nil {
+		return fmt.Errorf("cannot send empty error message: %w", err)
+	}
+
+	// Send response.
+	metricNamesCount := len(mns)
+	if err := ctx.writeUint64(uint64(metricNamesCount)); err != nil {
+		return fmt.Errorf("cannot send metricNamesCount: %w", err)
+	}
+	for i, mn := range mns {
+		ctx.dataBuf = mn.Marshal(ctx.dataBuf[:0])
+		if err := ctx.writeDataBufBytes(); err != nil {
+			return fmt.Errorf("cannot send metricName #%d: %w", i+1, err)
+		}
+	}
+	return nil
+}
+
+func (s *Server) processVMSelectSearch(ctx *vmselectRequestCtx) error {
+	vmselectSearchRequests.Inc()
+
+	// Read request.
+	if err := ctx.readSearchQuery(); err != nil {
+		return err
 	}
 	fetchData, err := ctx.readBool()
 	if err != nil {
@@ -1153,7 +1202,8 @@ var (
 	vmselectLabelEntriesRequests           = metrics.NewCounter("vm_vmselect_label_entries_requests_total")
 	vmselectSeriesCountRequests            = metrics.NewCounter("vm_vmselect_series_count_requests_total")
 	vmselectTSDBStatusRequests             = metrics.NewCounter("vm_vmselect_tsdb_status_requests_total")
-	vmselectSearchQueryRequests            = metrics.NewCounter("vm_vmselect_search_query_requests_total")
+	vmselectSearchMetricNamesRequests      = metrics.NewCounter("vm_vmselect_search_metric_names_requests_total")
+	vmselectSearchRequests                 = metrics.NewCounter("vm_vmselect_search_requests_total")
 	vmselectMetricBlocksRead               = metrics.NewCounter("vm_vmselect_metric_blocks_read_total")
 	vmselectMetricRowsRead                 = metrics.NewCounter("vm_vmselect_metric_rows_read_total")
 )

docs/Cluster-VictoriaMetrics.md

@@ -207,6 +207,7 @@ or [an alternative dashboard for VictoriaMetrics cluster](https://grafana.com/gr
       - `metrics/index.json` - returns all the metric names. See [these docs](https://graphite-api.readthedocs.io/en/latest/api.html#metrics-index-json).
       - `tags` - returns tag names. See [these docs](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags).
       - `tags/<tag_name>` - returns tag values for the given `<tag_name>`. See [these docs](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags).
+      - `tags/findSeries` - returns series matching the given `expr`. See [these docs](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags).
 
 * URL for time series deletion: `http://<vmselect>:8481/delete/<accountID>/prometheus/api/v1/admin/tsdb/delete_series?match[]=<timeseries_selector_for_delete>`.
   Note that the `delete_series` handler should be used only in exceptional cases such as deletion of accidentally ingested incorrect time series. It shouldn't

docs/Single-server-VictoriaMetrics.md

@@ -550,6 +550,7 @@ VictoriaMetrics supports the following handlers from [Graphite Tags API](https:/
 * [/tags/tagMultiSeries](https://graphite.readthedocs.io/en/stable/tags.html#adding-series-to-the-tagdb)
 * [/tags](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags)
 * [/tags/tag_name](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags)
+* [/tags/findSeries](https://graphite.readthedocs.io/en/stable/tags.html#exploring-tags)
 
 
 ### How to build from sources

lib/storage/storage.go

@@ -859,6 +859,44 @@ func nextRetentionDuration(retentionMonths int) time.Duration {
 	return deadline.Sub(t)
 }
 
+// SearchMetricNames returns metric names matching the given tfss on the given tr.
+func (s *Storage) SearchMetricNames(accountID, projectID uint32, tfss []*TagFilters, tr TimeRange, maxMetrics int, deadline uint64) ([]MetricName, error) {
+	tsids, err := s.searchTSIDs(tfss, tr, maxMetrics, deadline)
+	if err != nil {
+		return nil, err
+	}
+	if len(tsids) == 0 {
+		return nil, nil
+	}
+	if err = s.prefetchMetricNames(tsids, deadline); err != nil {
+		return nil, err
+	}
+	idb := s.idb()
+	is := idb.getIndexSearch(accountID, projectID, deadline)
+	defer idb.putIndexSearch(is)
+	mns := make([]MetricName, 0, len(tsids))
+	var metricName []byte
+	for i := range tsids {
+		metricID := tsids[i].MetricID
+		var err error
+		metricName, err = is.searchMetricName(metricName[:0], metricID)
+		if err != nil {
+			if err == io.EOF {
+				// Skip missing metricName for metricID.
+				// It should be automatically fixed. See indexDB.searchMetricName for details.
+				continue
+			}
+			return nil, fmt.Errorf("error when searching metricName for metricID=%d: %w", metricID, err)
+		}
+		mns = mns[:len(mns)+1]
+		mn := &mns[len(mns)-1]
+		if err = mn.Unmarshal(metricName); err != nil {
+			return nil, fmt.Errorf("cannot unmarshal metricName=%q: %w", metricName, err)
+		}
+	}
+	return mns, nil
+}
+
 // searchTSIDs returns sorted TSIDs for the given tfss and the given tr.
 func (s *Storage) searchTSIDs(tfss []*TagFilters, tr TimeRange, maxMetrics int, deadline uint64) ([]TSID, error) {
 	// Do not cache tfss -> tsids here, since the caching is performed