test: add load test with throughput and latency metrics

TestLoadTestThroughput: 1000 messages × 4 writes each = 4000 writes,
20 concurrent goroutines. Reports msgs/sec, p50/p95/p99 latency,
SQLITE_BUSY count, and total errors. Hard-asserts zero BUSY errors.

cmd/ingestor/db_test.go

@@ -4,7 +4,9 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
+	"sync/atomic"
 	"testing"
 	"time"
 )
@@ -790,3 +792,144 @@ func TestDBStats(t *testing.T) {
 	// LogStats should not panic
 	s.LogStats()
 }
+
+func TestLoadTestThroughput(t *testing.T) {
+	s, err := OpenStore(tempDBPath(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer s.Close()
+
+	// Pre-create observer
+	if err := s.UpsertObserver("obs1", "Observer1", "SJC"); err != nil {
+		t.Fatal(err)
+	}
+
+	const totalMessages = 1000
+	const goroutines = 20
+	perGoroutine := totalMessages / goroutines
+
+	// Simulate full pipeline: InsertTransmission + UpsertNode + UpsertObserver + IncrementAdvertCount
+	// This matches the real handleMessage write pattern for ADVERT packets
+	latencies := make([]time.Duration, totalMessages)
+	var busyErrors atomic.Int64
+	var totalErrors atomic.Int64
+	errCh := make(chan error, totalMessages)
+	done := make(chan struct{})
+
+	start := time.Now()
+
+	for g := 0; g < goroutines; g++ {
+		go func(gIdx int) {
+			defer func() { done <- struct{}{} }()
+			for i := 0; i < perGoroutine; i++ {
+				msgStart := time.Now()
+				idx := gIdx*perGoroutine + i
+				hash := fmt.Sprintf("load_%04d_%04d____", gIdx, i)
+				snr := 5.0
+				rssi := -100.0
+
+				data := &PacketData{
+					RawHex:      "0A00D69F",
+					Timestamp:   time.Now().UTC().Format(time.RFC3339),
+					ObserverID:  "obs1",
+					Hash:        hash[:16],
+					RouteType:   2,
+					PayloadType: 4,
+					PathJSON:    "[]",
+					DecodedJSON: `{"type":"ADVERT","pubKey":"` + hash[:16] + `"}`,
+					SNR:         &snr,
+					RSSI:        &rssi,
+				}
+
+				_, err := s.InsertTransmission(data)
+				if err != nil {
+					totalErrors.Add(1)
+					if strings.Contains(err.Error(), "database is locked") || strings.Contains(err.Error(), "SQLITE_BUSY") {
+						busyErrors.Add(1)
+					}
+					errCh <- err
+					continue
+				}
+
+				lat := 37.0 + float64(gIdx)*0.001
+				lon := -122.0 + float64(i)*0.001
+				pubKey := fmt.Sprintf("node_%04d_%04d____", gIdx, i)
+				if err := s.UpsertNode(pubKey[:16], "Node", "repeater", &lat, &lon, data.Timestamp); err != nil {
+					totalErrors.Add(1)
+					if strings.Contains(err.Error(), "locked") || strings.Contains(err.Error(), "BUSY") {
+						busyErrors.Add(1)
+					}
+				}
+
+				if err := s.IncrementAdvertCount(pubKey[:16]); err != nil {
+					totalErrors.Add(1)
+				}
+
+				obsID := fmt.Sprintf("obs_%04d_%04d_____", gIdx, i)
+				if err := s.UpsertObserver(obsID[:16], "Obs", "SJC"); err != nil {
+					totalErrors.Add(1)
+					if strings.Contains(err.Error(), "locked") || strings.Contains(err.Error(), "BUSY") {
+						busyErrors.Add(1)
+					}
+				}
+
+				latencies[idx] = time.Since(msgStart)
+			}
+		}(g)
+	}
+
+	for g := 0; g < goroutines; g++ {
+		<-done
+	}
+	close(errCh)
+	elapsed := time.Since(start)
+
+	// Calculate p50, p95, p99
+	validLatencies := make([]time.Duration, 0, totalMessages)
+	for _, l := range latencies {
+		if l > 0 {
+			validLatencies = append(validLatencies, l)
+		}
+	}
+	sort.Slice(validLatencies, func(i, j int) bool { return validLatencies[i] < validLatencies[j] })
+
+	p50 := validLatencies[len(validLatencies)*50/100]
+	p95 := validLatencies[len(validLatencies)*95/100]
+	p99 := validLatencies[len(validLatencies)*99/100]
+	msgsPerSec := float64(totalMessages) / elapsed.Seconds()
+
+	t.Logf("=== LOAD TEST RESULTS ===")
+	t.Logf("Messages:     %d (%d goroutines × %d each)", totalMessages, goroutines, perGoroutine)
+	t.Logf("Writes/msg:   4 (InsertTx + UpsertNode + IncrAdvertCount + UpsertObserver)")
+	t.Logf("Total writes: %d", totalMessages*4)
+	t.Logf("Duration:     %s", elapsed.Round(time.Millisecond))
+	t.Logf("Throughput:   %.1f msgs/sec (%.1f writes/sec)", msgsPerSec, msgsPerSec*4)
+	t.Logf("Latency p50:  %s", p50.Round(time.Microsecond))
+	t.Logf("Latency p95:  %s", p95.Round(time.Microsecond))
+	t.Logf("Latency p99:  %s", p99.Round(time.Microsecond))
+	t.Logf("SQLITE_BUSY:  %d", busyErrors.Load())
+	t.Logf("Total errors: %d", totalErrors.Load())
+	t.Logf("Stats: tx=%d dupes=%d obs=%d nodes=%d observers=%d write_err=%d",
+		s.Stats.TransmissionsInserted.Load(),
+		s.Stats.DuplicateTransmissions.Load(),
+		s.Stats.ObservationsInserted.Load(),
+		s.Stats.NodeUpserts.Load(),
+		s.Stats.ObserverUpserts.Load(),
+		s.Stats.WriteErrors.Load(),
+	)
+
+	// Hard assertions
+	if busyErrors.Load() > 0 {
+		t.Errorf("SQLITE_BUSY errors: %d (expected 0)", busyErrors.Load())
+	}
+	if totalErrors.Load() > 0 {
+		t.Errorf("Total errors: %d (expected 0)", totalErrors.Load())
+	}
+
+	var txCount int
+	s.db.QueryRow("SELECT COUNT(*) FROM transmissions").Scan(&txCount)
+	if txCount != totalMessages {
+		t.Errorf("transmissions=%d, want %d", txCount, totalMessages)
+	}
+}