app/vmselect: de-duplicate data exported via /api/v1/export/csv by default

Previously the exported data wasn't de-duplicated.
Now it is possible to export the raw data without deduplication
by passing reduce_mem_usage=1 query arg to /api/v1/export/csv

See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1837

README.md

@@ -837,7 +837,7 @@ unix timestamp in seconds or [RFC3339](https://www.ietf.org/rfc/rfc3339.txt) val
 
 The exported CSV data can be imported to VictoriaMetrics via [/api/v1/import/csv](#how-to-import-csv-data).
 
-The [deduplication](#deduplication) isn't applied for the data exported in CSV. It is expected that the de-duplication is performed during data import.
+The [deduplication](#deduplication) is applied for the data exported in CSV by default. It is possible to export raw data without de-duplication by passing `reduce_mem_usage=1` query arg to `/api/v1/export/csv`.
 
 
 ### How to export data in native format

app/vmselect/prometheus/prometheus.go

@@ -129,6 +129,7 @@ func ExportCSVHandler(startTime time.Time, w http.ResponseWriter, r *http.Reques
 	if err != nil {
 		return err
 	}
+	reduceMemUsage := searchutils.GetBool(r, "reduce_mem_usage")
 	deadline := searchutils.GetDeadlineForExport(r, startTime)
 	tagFilterss, err := getTagFilterssFromRequest(r)
 	if err != nil {
@@ -140,7 +141,38 @@ func ExportCSVHandler(startTime time.Time, w http.ResponseWriter, r *http.Reques
 	defer bufferedwriter.Put(bw)
 
 	resultsCh := make(chan *quicktemplate.ByteBuffer, cgroup.AvailableCPUs())
-	doneCh := make(chan error)
+	writeCSVLine := func(xb *exportBlock) {
+		if len(xb.timestamps) == 0 {
+			return
+		}
+		bb := quicktemplate.AcquireByteBuffer()
+		WriteExportCSVLine(bb, xb, fieldNames)
+		resultsCh <- bb
+	}
+	doneCh := make(chan error, 1)
+	if !reduceMemUsage {
+		rss, err := netstorage.ProcessSearchQuery(sq, true, deadline)
+		if err != nil {
+			return fmt.Errorf("cannot fetch data for %q: %w", sq, err)
+		}
+		go func() {
+			err := rss.RunParallel(func(rs *netstorage.Result, workerID uint) error {
+				if err := bw.Error(); err != nil {
+					return err
+				}
+				xb := exportBlockPool.Get().(*exportBlock)
+				xb.mn = &rs.MetricName
+				xb.timestamps = rs.Timestamps
+				xb.values = rs.Values
+				writeCSVLine(xb)
+				xb.reset()
+				exportBlockPool.Put(xb)
+				return nil
+			})
+			close(resultsCh)
+			doneCh <- err
+		}()
+	} else {
 		go func() {
 			err := netstorage.ExportBlocks(sq, deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange) error {
 				if err := bw.Error(); err != nil {
@@ -152,11 +184,7 @@ func ExportCSVHandler(startTime time.Time, w http.ResponseWriter, r *http.Reques
 				xb := exportBlockPool.Get().(*exportBlock)
 				xb.mn = mn
 				xb.timestamps, xb.values = b.AppendRowsWithTimeRangeFilter(xb.timestamps[:0], xb.values[:0], tr)
-			if len(xb.timestamps) > 0 {
+				writeCSVLine(xb)
-				bb := quicktemplate.AcquireByteBuffer()
-				WriteExportCSVLine(bb, xb, fieldNames)
-				resultsCh <- bb
-			}
 				xb.reset()
 				exportBlockPool.Put(xb)
 				return nil
@@ -164,6 +192,7 @@ func ExportCSVHandler(startTime time.Time, w http.ResponseWriter, r *http.Reques
 			close(resultsCh)
 			doneCh <- err
 		}()
+	}
 	// Consume all the data from resultsCh.
 	for bb := range resultsCh {
 		// Do not check for error in bw.Write, since this error is checked inside netstorage.ExportBlocks above.
@@ -360,7 +389,7 @@ func exportHandler(w http.ResponseWriter, matches []string, etfs [][]storage.Tag
 	defer bufferedwriter.Put(bw)
 
 	resultsCh := make(chan *quicktemplate.ByteBuffer, cgroup.AvailableCPUs())
-	doneCh := make(chan error)
+	doneCh := make(chan error, 1)
 	if !reduceMemUsage {
 		rss, err := netstorage.ProcessSearchQuery(sq, true, deadline)
 		if err != nil {

docs/CHANGELOG.md

@@ -24,6 +24,7 @@ sort: 15
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix navigation over query history with `Ctrl+up/down` and fix zoom relatively to the cursor position. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/1936).
 * BUGFIX: deduplicate samples more thoroughly if [deduplication](https://docs.victoriametrics.com/#deduplication) is enabled. Previously some duplicate samples may be left on disk for time series with high churn rate. This may result in bigger storage space requirements.
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): follow up to 5 redirects when `follow_redirects: true` is set for a particular scrape config. Previously only a single redirect was performed in this case. It is expected these redirects are performed to the original hostname. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1945).
+* BUGFIX: de-duplicate data exported via [/api/v1/export/csv](https://docs.victoriametrics.com/#how-to-export-csv-data) by default if [deduplication](https://docs.victoriametrics.com/#deduplication) is enabled. The de-duplication can be disabled by passing `reduce_mem_usage=1` query arg to `/api/v1/export/csv`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1837).
 
 
 ## [v1.70.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.70.0)

docs/README.md

@@ -837,7 +837,7 @@ unix timestamp in seconds or [RFC3339](https://www.ietf.org/rfc/rfc3339.txt) val
 
 The exported CSV data can be imported to VictoriaMetrics via [/api/v1/import/csv](#how-to-import-csv-data).
 
-The [deduplication](#deduplication) isn't applied for the data exported in CSV. It is expected that the de-duplication is performed during data import.
+The [deduplication](#deduplication) is applied for the data exported in CSV by default. It is possible to export raw data without de-duplication by passing `reduce_mem_usage=1` query arg to `/api/v1/export/csv`.
 
 
 ### How to export data in native format

docs/Single-server-VictoriaMetrics.md

@@ -841,7 +841,7 @@ unix timestamp in seconds or [RFC3339](https://www.ietf.org/rfc/rfc3339.txt) val
 
 The exported CSV data can be imported to VictoriaMetrics via [/api/v1/import/csv](#how-to-import-csv-data).
 
-The [deduplication](#deduplication) isn't applied for the data exported in CSV. It is expected that the de-duplication is performed during data import.
+The [deduplication](#deduplication) is applied for the data exported in CSV by default. It is possible to export raw data without de-duplication by passing `reduce_mem_usage=1` query arg to `/api/v1/export/csv`.
 
 
 ### How to export data in native format