Regex set optimisation when looking series in ingester (grafana#2475)

* Regex set optimisation when looking series in ingester

Similar to cortexproject/cortex#2446

Super useful for templated grafana dashboards which send matchers such
as =~"a|b|c|d|e"

Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>

* Add CHANGELOG entry

Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>

* Add benchmark for set optimisation

Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>

chunk_store.go

@@ -441,8 +441,8 @@ func (c *baseStore) lookupIdsByMetricNameMatcher(ctx context.Context, from, thro
 	} else if matcher.Type == labels.MatchEqual {
 		labelName = matcher.Name
 		queries, err = c.schema.GetReadQueriesForMetricLabelValue(from, through, userID, metricName, matcher.Name, matcher.Value)
-	} else if matcher.Type == labels.MatchRegexp && len(findSetMatches(matcher.Value)) > 0 {
-		set := findSetMatches(matcher.Value)
+	} else if matcher.Type == labels.MatchRegexp && len(FindSetMatches(matcher.Value)) > 0 {
+		set := FindSetMatches(matcher.Value)
 		for _, v := range set {
 			var qs []IndexQuery
 			qs, err = c.schema.GetReadQueriesForMetricLabelValue(from, through, userID, metricName, matcher.Name, v)

opts.go

@@ -19,9 +19,9 @@ func init() {
 	}
 }
 
+// FindSetMatches returns list of values that can be equality matched on.
 // copied from Prometheus querier.go, removed check for Prometheus wrapper.
-// Returns list of values that can regex matches.
-func findSetMatches(pattern string) []string {
+func FindSetMatches(pattern string) []string {
 	escaped := false
 	sets := []*strings.Builder{{}}
 	for i := 0; i < len(pattern); i++ {

opts_test.go

@@ -44,7 +44,7 @@ func TestFindSetMatches(t *testing.T) {
 	}
 
 	for _, c := range cases {
-		matches := findSetMatches(c.pattern)
+		matches := FindSetMatches(c.pattern)
 		require.Equal(t, c.exp, matches)
 	}
 }