lib/promscrape: allow using sample_limit and series_limit options in stream parsing mode

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3458

app/vmagent/README.md

@@ -654,8 +654,9 @@ scrape_configs:
     'match[]': ['{__name__!=""}']
 ```
 
-Note that `sample_limit` and `series_limit` [scrape_config options](https://docs.victoriametrics.com/sd_configs.html#scrape_configs)
-cannot be used in stream parsing mode because the parsed data is pushed to remote storage as soon as it is parsed.
+Note that `vmagent` in stream parsing mode stores up to `sample_limit` samples to the configured `-remoteStorage.url`
+instead of droping all the samples read from the target, because the parsed data is sent to the remote storage
+as soon as it is parsed in stream parsing mode.
 
 ## Scraping big number of targets
 
@@ -744,8 +745,8 @@ By default `vmagent` doesn't limit the number of time series each scrape target
 
 * Via `-promscrape.seriesLimitPerTarget` command-line option. This limit is applied individually
   to all the scrape targets defined in the file pointed by `-promscrape.config`.
-* Via `series_limit` config option at `scrape_config` section. This limit is applied individually
-  to all the scrape targets defined in the given `scrape_config`.
+* Via `series_limit` config option at [scrape_config](https://docs.victoriametrics.com/sd_configs.html#scrape_configs) section.
+  This limit is applied individually to all the scrape targets defined in the given `scrape_config`.
 * Via `__series_limit__` label, which can be set with [relabeling](#relabeling) at `relabel_configs` section.
   This limit is applied to the corresponding scrape targets. Typical use case: to set the limit
   via [Kubernetes annotations](https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/) for targets,

docs/CHANGELOG.md

@@ -47,6 +47,8 @@ The following tip changes can be tested by building VictoriaMetrics components f
   * `vm_rows{type="indexdb/file"}` - the total number of file-based `indexdb` rows
 * FEATURE: [DataDog parser](https://docs.victoriametrics.com/#how-to-send-data-from-datadog-agent): add `device` tag when it is passed in the `device` field is present in the `series` object of the input request. Thanks to @PerGon for the provided [pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/3431).
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): improve [service discovery](https://docs.victoriametrics.com/sd_configs.html) performance when discovering big number of targets (10K and more).
+* FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): allow using `series_limit` option for [limiting the number of series a single scrape target generates](https://docs.victoriametrics.com/vmagent.html#cardinality-limiter) in [stream parsing mode](https://docs.victoriametrics.com/vmagent.html#stream-parsing-mode). See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3458).
+* FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): allow using `sample_limit` option for limiting the number of metrics a single scrape target can expose in every response sent over [stream parsing mode](https://docs.victoriametrics.com/vmagent.html#stream-parsing-mode).
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): add `exported_` prefix to metric names exported by scrape targets if these metric names clash with [automatically generated metrics](https://docs.victoriametrics.com/vmagent.html#automatically-generated-metrics) such as `up`, `scrape_samples_scraped`, etc. This prevents from corruption of automatically generated metrics. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3406).
 * FEATURE: [VictoriaMetrics cluster](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): improve error message when the requested path cannot be properly parsed, so users could identify the issue and properly fix the path. Now the error message links to [url format docs](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#url-format). See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3402).
 * FEATURE: [VictoriaMetrics enterprise cluster](https://docs.victoriametrics.com/enterprise.html): add `-storageNode.discoveryInterval` command-line flag to `vmselect` and `vminsert` to control load on DNS servers when [automatic discovery of vmstorage nodes](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#automatic-vmstorage-discovery) is enabled. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3417).

lib/promscrape/config.go

@@ -936,12 +936,6 @@ func getScrapeWorkConfig(sc *ScrapeConfig, baseDir string, globalCfg *GlobalConf
 	if err != nil {
 		return nil, fmt.Errorf("cannot parse `metric_relabel_configs` for `job_name` %q: %w", jobName, err)
 	}
-	if (*streamParse || sc.StreamParse) && sc.SampleLimit > 0 {
-		return nil, fmt.Errorf("cannot use stream parsing mode when `sample_limit` is set for `job_name` %q", jobName)
-	}
-	if (*streamParse || sc.StreamParse) && sc.SeriesLimit > 0 {
-		return nil, fmt.Errorf("cannot use stream parsing mode when `series_limit` is set for `job_name` %q", jobName)
-	}
 	externalLabels := globalCfg.ExternalLabels
 	noStaleTracking := *noStaleMarkers
 	if sc.NoStaleMarkers != nil {

lib/promscrape/scrapework.go

@@ -543,6 +543,10 @@ func (sw *scrapeWork) scrapeStream(scrapeTimestamp, realTimestamp int64) error {
 	// Do not pool sbr and do not pre-allocate sbr.body in order to reduce memory usage when scraping big responses.
 	var sbr streamBodyReader
 
+	lastScrape := sw.loadLastScrape()
+	bodyString := ""
+	areIdenticalSeries := true
+	samplesDropped := 0
 	sr, err := sw.GetStreamReader()
 	if err != nil {
 		err = fmt.Errorf("cannot read data: %s", err)
@@ -550,6 +554,8 @@ func (sw *scrapeWork) scrapeStream(scrapeTimestamp, realTimestamp int64) error {
 		var mu sync.Mutex
 		err = sbr.Init(sr)
 		if err == nil {
+			bodyString = bytesutil.ToUnsafeString(sbr.body)
+			areIdenticalSeries = sw.Config.NoStaleMarkers || parser.AreIdenticalSeriesFast(lastScrape, bodyString)
 			err = parser.ParseStream(&sbr, scrapeTimestamp, false, func(rows []parser.Row) error {
 				mu.Lock()
 				defer mu.Unlock()
@@ -557,9 +563,6 @@ func (sw *scrapeWork) scrapeStream(scrapeTimestamp, realTimestamp int64) error {
 				for i := range rows {
 					sw.addRowToTimeseries(wc, &rows[i], scrapeTimestamp, true)
 				}
-				// Push the collected rows to sw before returning from the callback, since they cannot be held
-				// after returning from the callback - this will result in data race.
-				// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/825#issuecomment-723198247
 				samplesPostRelabeling += len(wc.writeRequest.Timeseries)
 				if sw.Config.SampleLimit > 0 && samplesPostRelabeling > sw.Config.SampleLimit {
 					wc.resetNoRows()
@@ -567,6 +570,15 @@ func (sw *scrapeWork) scrapeStream(scrapeTimestamp, realTimestamp int64) error {
 					return fmt.Errorf("the response from %q exceeds sample_limit=%d; "+
 						"either reduce the sample count for the target or increase sample_limit", sw.Config.ScrapeURL, sw.Config.SampleLimit)
 				}
+				if sw.seriesLimitExceeded || !areIdenticalSeries {
+					samplesDropped += sw.applySeriesLimit(wc)
+					if samplesDropped > 0 && !sw.seriesLimitExceeded {
+						sw.seriesLimitExceeded = true
+					}
+				}
+				// Push the collected rows to sw before returning from the callback, since they cannot be held
+				// after returning from the callback - this will result in data race.
+				// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/825#issuecomment-723198247
 				sw.pushData(sw.Config.AuthToken, &wc.writeRequest)
 				wc.resetNoRows()
 				return nil
@@ -574,9 +586,6 @@ func (sw *scrapeWork) scrapeStream(scrapeTimestamp, realTimestamp int64) error {
 		}
 		sr.MustClose()
 	}
-	lastScrape := sw.loadLastScrape()
-	bodyString := bytesutil.ToUnsafeString(sbr.body)
-	areIdenticalSeries := sw.Config.NoStaleMarkers || parser.AreIdenticalSeriesFast(lastScrape, bodyString)
 
 	scrapedSamples.Update(float64(samplesScraped))
 	endTimestamp := time.Now().UnixNano() / 1e6
@@ -603,6 +612,7 @@ func (sw *scrapeWork) scrapeStream(scrapeTimestamp, realTimestamp int64) error {
 		samplesScraped:            samplesScraped,
 		samplesPostRelabeling:     samplesPostRelabeling,
 		seriesAdded:               seriesAdded,
+		seriesLimitSamplesDropped: samplesDropped,
 	}
 	sw.addAutoMetrics(am, wc, scrapeTimestamp)
 	sw.pushData(sw.Config.AuthToken, &wc.writeRequest)