Fix v2 function names in ClickHouse queries

pkg/clickhouse/ingester_test.go

@@ -79,6 +79,24 @@ func TestDecodeLineInfoNoMapping(t *testing.T) {
 	require.Equal(t, "app/importer.py", info.FunctionFilename)
 }
 
+func TestDecodeLineInfoV2SystemName(t *testing.T) {
+	stringTable := []string{"", "decode_system", "app/importer.py"}
+	encoded := profile.EncodePprofLocation(
+		&pprofpb.Location{
+			Address: 0x47,
+			Line:    []*pprofpb.Line{{FunctionId: 1, Line: 7}},
+		},
+		nil,
+		[]*pprofpb.Function{{SystemName: 1, Filename: 2}},
+		stringTable,
+	)
+
+	info := decodeLineInfo(encoded)
+	require.Empty(t, info.FunctionName)
+	require.Equal(t, "decode_system", info.FunctionSystemName)
+	require.Equal(t, "app/importer.py", info.FunctionFilename)
+}
+
 // Native frames are sent unsymbolized (no lines); nothing should be decoded.
 func TestDecodeLineInfoUnsymbolizedFrame(t *testing.T) {
 	stringTable := []string{"", "build-id-456", "libc.so.6"}

pkg/clickhouse/querier.go

@@ -835,6 +835,13 @@ type sampleData struct {
 	period              int64
 }
 
+func (s sampleData) hasStoredFunction(i int) bool {
+	return (i < len(s.functionNames) && s.functionNames[i] != "") ||
+		(i < len(s.functionSystemNames) && s.functionSystemNames[i] != "") ||
+		(i < len(s.functionFilenames) && s.functionFilenames[i] != "") ||
+		(i < len(s.functionStartLines) && s.functionStartLines[i] != 0)
+}
+
 // rowsToArrowRecords converts ClickHouse query results to Arrow records.
 func (q *Querier) rowsToArrowRecords(
 	ctx context.Context,
@@ -884,8 +891,8 @@ func (q *Querier) rowsToArrowRecords(
 			}
 			addr := s.addresses[i]
 
-			// Check if this location needs symbolization (no function name but has build ID)
-			needsSymbolization := (i >= len(s.functionNames) || s.functionNames[i] == "") && buildID != "" && addr != 0
+			// Symbolize only when no stored function metadata is available.
+			needsSymbolization := !s.hasStoredFunction(i) && buildID != "" && addr != 0
 
 			if needsSymbolization {
 				if _, ok := locationIndex[buildID]; !ok {
@@ -1037,8 +1044,9 @@ func (q *Querier) rowsToArrowRecords(
 						w.FunctionStartLine.AppendNull()
 					}
 				}
-			} else if idx < len(s.functionNames) && s.functionNames[idx] != "" {
-				// Use stored function data
+			} else if s.hasStoredFunction(idx) {
+				// Use stored function data, including v2 rows where only the
+				// system name is populated.
 				w.Lines.Append(true)
 				w.Line.Append(true)
 				if idx < len(s.lineNumbers) {

pkg/clickhouse/querier_test.go

@@ -0,0 +1,26 @@
+// Copyright 2026 The Parca Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package clickhouse
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSampleDataHasStoredFunction(t *testing.T) {
+	require.True(t, (sampleData{functionSystemNames: []string{"local_function"}}).hasStoredFunction(0))
+	require.True(t, (sampleData{functionNames: []string{"function"}}).hasStoredFunction(0))
+	require.False(t, (sampleData{functionNames: []string{""}, functionSystemNames: []string{""}}).hasStoredFunction(0))
+}