feat: Introduce shardable probabilistic topk for instant queries.

docs/sources/shared/configuration.md

@@ -130,6 +130,11 @@ querier_rf1:
     # CLI flag: -querier-rf1.engine.max-lookback-period
     [max_look_back_period: <duration> | default = 30s]
 
+    # The maximum number of labels the heap of a topk query using a count min
+    # sketch can track.
+    # CLI flag: -querier-rf1.engine.max-count-min-sketch-heap-size
+    [max_count_min_sketch_heap_size: <int> | default = 10000]
+
   # The maximum number of queries that can be simultaneously processed by the
   # querier.
   # CLI flag: -querier-rf1.max-concurrent
@@ -3841,6 +3846,9 @@ otlp_config:
 # CLI flag: -limits.ingestion-partition-tenant-shard-size
 [ingestion_partitions_tenant_shard_size: <int> | default = 0]
 
+# List of LogQL vector and range aggregations that should be sharded.
+[shard_aggregations: <list of strings>]
+
 # Enable metric aggregation. When enabled, pushed streams will be sampled for
 # bytes and count, and these metric will be written back into Loki as a special
 # __aggregated_metric__ stream, which can be queried for faster histogram
@@ -4245,6 +4253,11 @@ engine:
   # CLI flag: -querier.engine.max-lookback-period
   [max_look_back_period: <duration> | default = 30s]
 
+  # The maximum number of labels the heap of a topk query using a count min
+  # sketch can track.
+  # CLI flag: -querier.engine.max-count-min-sketch-heap-size
+  [max_count_min_sketch_heap_size: <int> | default = 10000]
+
 # The maximum number of queries that can be simultaneously processed by the
 # querier.
 # CLI flag: -querier.max-concurrent

integration/loki_micro_services_test.go

@@ -94,7 +94,7 @@ func TestMicroServicesIngestQuery(t *testing.T) {
 			"-common.compactor-address="+tCompactor.HTTPURL(),
 			"-querier.per-request-limits-enabled=true",
 			"-frontend.encoding=protobuf",
-			"-querier.shard-aggregations=quantile_over_time",
+			"-querier.shard-aggregations=quantile_over_time,approx_topk",
 			"-frontend.tail-proxy-url="+tQuerier.HTTPURL(),
 		)
 	)
@@ -784,6 +784,115 @@ func TestOTLPLogsIngestQuery(t *testing.T) {
 	})
 }
 
+func TestProbabilisticQuery(t *testing.T) {
+	clu := cluster.New(nil, cluster.SchemaWithTSDBAndTSDB, func(c *cluster.Cluster) {
+		c.SetSchemaVer("v13")
+	})
+	defer func() {
+		assert.NoError(t, clu.Cleanup())
+	}()
+
+	// run initially the compactor, indexgateway, and distributor.
+	var (
+		tCompactor = clu.AddComponent(
+			"compactor",
+			"-target=compactor",
+			"-compactor.compaction-interval=1s",
+			"-compactor.retention-delete-delay=1s",
+			// By default, a minute is added to the delete request start time. This compensates for that.
+			"-compactor.delete-request-cancel-period=-60s",
+			"-compactor.deletion-mode=filter-and-delete",
+		)
+		tIndexGateway = clu.AddComponent(
+			"index-gateway",
+			"-target=index-gateway",
+		)
+		tDistributor = clu.AddComponent(
+			"distributor",
+			"-target=distributor",
+		)
+	)
+	require.NoError(t, clu.Run())
+
+	// then, run only the ingester and query scheduler.
+	var (
+		tIngester = clu.AddComponent(
+			"ingester",
+			"-target=ingester",
+			"-boltdb.shipper.index-gateway-client.server-address="+tIndexGateway.GRPCURL(),
+		)
+		tQueryScheduler = clu.AddComponent(
+			"query-scheduler",
+			"-target=query-scheduler",
+			"-query-scheduler.use-scheduler-ring=false",
+			"-boltdb.shipper.index-gateway-client.server-address="+tIndexGateway.GRPCURL(),
+		)
+	)
+	require.NoError(t, clu.Run())
+
+	// the run querier.
+	var (
+		tQuerier = clu.AddComponent(
+			"querier",
+			"-target=querier",
+			"-querier.scheduler-address="+tQueryScheduler.GRPCURL(),
+			"-boltdb.shipper.index-gateway-client.server-address="+tIndexGateway.GRPCURL(),
+			"-common.compactor-address="+tCompactor.HTTPURL(),
+		)
+	)
+	require.NoError(t, clu.Run())
+
+	// finally, run the query-frontend.
+	var (
+		tQueryFrontend = clu.AddComponent(
+			"query-frontend",
+			"-target=query-frontend",
+			"-frontend.scheduler-address="+tQueryScheduler.GRPCURL(),
+			"-boltdb.shipper.index-gateway-client.server-address="+tIndexGateway.GRPCURL(),
+			"-common.compactor-address="+tCompactor.HTTPURL(),
+			"-querier.per-request-limits-enabled=true",
+			"-frontend.encoding=protobuf",
+			"-querier.shard-aggregations=quantile_over_time,approx_topk",
+			"-frontend.tail-proxy-url="+tQuerier.HTTPURL(),
+		)
+	)
+	require.NoError(t, clu.Run())
+
+	tenantID := randStringRunes()
+
+	now := time.Now()
+	cliDistributor := client.New(tenantID, "", tDistributor.HTTPURL())
+	cliDistributor.Now = now
+	cliIngester := client.New(tenantID, "", tIngester.HTTPURL())
+	cliIngester.Now = now
+	cliQueryFrontend := client.New(tenantID, "", tQueryFrontend.HTTPURL())
+	cliQueryFrontend.Now = now
+
+	t.Run("ingest-logs", func(t *testing.T) {
+		// ingest some log lines
+		require.NoError(t, cliDistributor.PushLogLine("lineA", now.Add(-45*time.Minute), nil, map[string]string{"job": "one"}))
+		require.NoError(t, cliDistributor.PushLogLine("lineB", now.Add(-45*time.Minute), nil, map[string]string{"job": "one"}))
+
+		require.NoError(t, cliDistributor.PushLogLine("lineC", now, nil, map[string]string{"job": "one"}))
+		require.NoError(t, cliDistributor.PushLogLine("lineD", now, nil, map[string]string{"job": "two"}))
+	})
+
+	t.Run("query", func(t *testing.T) {
+		resp, err := cliQueryFrontend.RunQuery(context.Background(), `approx_topk(1, count_over_time({job=~".+"}[1h]))`)
+		require.NoError(t, err)
+		assert.Equal(t, "vector", resp.Data.ResultType)
+
+		var values []string
+		var labels []string
+		for _, value := range resp.Data.Vector {
+			values = append(values, value.Value)
+			labels = append(labels, value.Metric["job"])
+		}
+		assert.ElementsMatch(t, []string{"3"}, values)
+		assert.ElementsMatch(t, []string{"one"}, labels)
+	})
+}
+
 func TestCategorizedLabels(t *testing.T) {
 	clu := cluster.New(nil, cluster.SchemaWithTSDB, func(c *cluster.Cluster) {
 		c.SetSchemaVer("v13")