store: use k-way merging for proxying logic

CHANGELOG.md

@@ -20,6 +20,8 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 ### Changed
 
+- [#5255](https://github.com/thanos-io/thanos/pull/5296) Query: Use k-way merging for the proxying logic. The proxying sub-system now uses much less resources (~25-80% less CPU usage, ~30-50% less RAM usage according to our benchmarks). Reduces query duration by a few percent on queries with lots of series.
+
 ### Removed
 
 ## [v0.28.0](https://github.com/thanos-io/thanos/tree/release-0.28) - 2022.08.26

cmd/thanos/query.go

@@ -182,6 +182,7 @@ func registerQuery(app *extkingpin.App) {
 	reqLogConfig := extkingpin.RegisterRequestLoggingFlags(cmd)
 
 	alertQueryURL := cmd.Flag("alert.query-url", "The external Thanos Query URL that would be set in all alerts 'Source' field.").String()
+	grpcProxyStrategy := cmd.Flag("grpc.proxy-strategy", "Strategy to use when proxying Series requests to leaf nodes. Hidden and only used for testing, will be removed after lazy becomes the default.").Default(string(store.EagerRetrieval)).Hidden().Enum(string(store.EagerRetrieval), string(store.LazyRetrieval))
 
 	cmd.Setup(func(g *run.Group, logger log.Logger, reg *prometheus.Registry, tracer opentracing.Tracer, _ <-chan struct{}, _ bool) error {
 		selectorLset, err := parseFlagLabels(*selectorLabels)
@@ -292,6 +293,7 @@ func registerQuery(app *extkingpin.App) {
 			*webDisableCORS,
 			enableQueryPushdown,
 			*alertQueryURL,
+			*grpcProxyStrategy,
 			component.Query,
 		)
 	})
@@ -362,6 +364,7 @@ func runQuery(
 	disableCORS bool,
 	enableQueryPushdown bool,
 	alertQueryURL string,
+	grpcProxyStrategy string,
 	comp component.Component,
 ) error {
 	if alertQueryURL == "" {
@@ -472,7 +475,7 @@ func runQuery(
 			unhealthyStoreTimeout,
 			endpointInfoTimeout,
 		)
-		proxy            = store.NewProxyStore(logger, reg, endpoints.GetStoreClients, component.Query, selectorLset, storeResponseTimeout)
+		proxy            = store.NewProxyStore(logger, reg, endpoints.GetStoreClients, component.Query, selectorLset, storeResponseTimeout, store.RetrievalStrategy(grpcProxyStrategy))
 		rulesProxy       = rules.NewProxy(logger, endpoints.GetRulesClients)
 		targetsProxy     = targets.NewProxy(logger, endpoints.GetTargetsClients)
 		metadataProxy    = metadata.NewProxy(logger, endpoints.GetMetricMetadataClients)

pkg/query/query_test.go

@@ -36,7 +36,7 @@ func TestQuerier_Proxy(t *testing.T) {
 			logger,
 			nil,
 			store.NewProxyStore(logger, nil, func() []store.Client { return clients },
-				component.Debug, nil, 5*time.Minute),
+				component.Debug, nil, 5*time.Minute, store.EagerRetrieval),
 			1000000,
 			5*time.Minute,
 		)