diff --git a/docs/ops/go-vehicle-ingest-memory.md b/docs/ops/go-vehicle-ingest-memory.md
index d46813e3..1d7e1558 100644
--- a/docs/ops/go-vehicle-ingest-memory.md
+++ b/docs/ops/go-vehicle-ingest-memory.md
@@ -440,7 +440,7 @@ FAST_WRITER_TDENGINE_MAX_OPEN_CONNS
 FAST_WRITER_TDENGINE_MAX_IDLE_CONNS
 ```
 
-默认 `max_open=1`、`max_idle=1`。原因是当前 TDengine 写入依赖启动时执行的 `USE <database>`；`database/sql` 连接池新建连接不会继承其他连接上的 `USE` 状态。实测默认跟随 worker 放大到 8 会导致 `[0x200] db is not specified` / `[0x2616] Database not specified`。后续只有在 TDengine DSN 或 writer SQL 改为每条连接都明确选库后，才能提高该连接池。
+默认 `max_open=1`、`max_idle=1`，生产可以通过 env 小步放大。此前实测默认跟随 worker 放大到 8 会导致 `[0x200] db is not specified` / `[0x2616] Database not specified`，根因是 TDengine `USE <database>` 不会自动作用到 `database/sql` 新建连接。2026-07-03 已将 fast-writer 使用的 history writer 改为生成 `database.table` 形式的 database-qualified SQL，并在 ECS 上将 pool 调到 `2/2` 验证通过：未再出现选库错误，写入 ok 计数持续增长。
 
 同时新增 batch pending gauge：
 
diff --git a/docs/ops/vehicle-ingest-runbook.md b/docs/ops/vehicle-ingest-runbook.md
index 94d617d1..93b57ea5 100644
--- a/docs/ops/vehicle-ingest-runbook.md
+++ b/docs/ops/vehicle-ingest-runbook.md
@@ -136,7 +136,7 @@ go run ./cmd/load-sim \
 | `vehicle_fast_writer_nats_consumer_pending` | 持续增长且 `> 10000` | fast-writer 消费 NATS 的速度跟不上入口写入速度。 |
 | `vehicle_fast_writer_batch_pending_messages` | 持续非 0 或 burst 后不回落 | fast-writer 已拉取 NATS 消息但尚未完成 TDengine/Redis 写入和 ack。 |
 | `vehicle_fast_writer_batch_pending_envelopes` | 持续非 0 或 burst 后不回落 | fast-writer 当前批次已有有效 envelope 在等待落库或 ack。 |
-| `vehicle_fast_writer_stage_duration_ms_histogram_bucket` | 某个 stage 的 p99 连续 5 分钟上升 | NATS 快速写链路在 TDengine、Redis 或 NATS ack 某一阶段变慢；当前 TDengine 连接池默认保持 `1`，放大 `FAST_WRITER_TDENGINE_MAX_OPEN_CONNS` 前必须先确认每条连接都能明确选库。 |
+| `vehicle_fast_writer_stage_duration_ms_histogram_bucket` | 某个 stage 的 p99 连续 5 分钟上升 | NATS 快速写链路在 TDengine、Redis 或 NATS ack 某一阶段变慢；TDengine 阶段可小步调整 `FAST_WRITER_TDENGINE_MAX_OPEN_CONNS`，调整后必须观察是否出现选库错误和 ack-pending 增长。 |
 | `vehicle_realtime_store_update_duration_ms_histogram_bucket{store="redis"}` | p99 连续 5 分钟上升 | Redis 实时投影变慢，会直接影响 realtime consumer 追平能力。 |
 | `vehicle_realtime_store_update_duration_ms_histogram_bucket{store="mysql"}` | p99 连续 5 分钟上升 | MySQL 当前态/位置投影变慢，需结合 async queue depth 和 dropped 计数判断。 |
 | `vehicle_stat_write_duration_ms_histogram_bucket` | p99 连续 5 分钟上升 | MySQL 每日里程统计写入变慢，可能导致 stat Kafka lag 增长。 |
diff --git a/go/vehicle-gateway/cmd/nats-fast-writer/main.go b/go/vehicle-gateway/cmd/nats-fast-writer/main.go
index e7fc1013..2013d9c7 100644
--- a/go/vehicle-gateway/cmd/nats-fast-writer/main.go
+++ b/go/vehicle-gateway/cmd/nats-fast-writer/main.go
@@ -72,19 +72,13 @@ func main() {
 		logger.Error("tdengine ping failed", "error", err)
 		os.Exit(1)
 	}
-	historyWriter := history.NewWriter(tdDB)
+	historyWriter := history.NewWriterWithDatabase(tdDB, cfg.TDengineDatabase)
 	if cfg.TDengineEnsureSchema {
 		if err := historyWriter.EnsureSchema(ctx, cfg.TDengineDatabase); err != nil {
 			logger.Error("tdengine schema bootstrap failed", "error", err)
 			os.Exit(1)
 		}
 	}
-	if strings.TrimSpace(cfg.TDengineDatabase) != "" {
-		if _, err := tdDB.ExecContext(ctx, "USE "+cfg.TDengineDatabase); err != nil {
-			logger.Error("tdengine use database failed", "database", cfg.TDengineDatabase, "error", err)
-			os.Exit(1)
-		}
-	}
 
 	redisClient := redis.NewClient(&redis.Options{
 		Addr:     cfg.RedisAddr,
diff --git a/go/vehicle-gateway/internal/history/writer.go b/go/vehicle-gateway/internal/history/writer.go
index 69bce4fb..7e627c47 100644
--- a/go/vehicle-gateway/internal/history/writer.go
+++ b/go/vehicle-gateway/internal/history/writer.go
@@ -22,8 +22,9 @@ type Execer interface {
 }
 
 type Writer struct {
-	exec  Execer
-	cache tableCache
+	exec     Execer
+	database string
+	cache    tableCache
 }
 
 const (
@@ -50,6 +51,12 @@ func NewWriter(exec Execer) *Writer {
 	return &Writer{exec: exec, cache: tableCache{seen: map[string]struct{}{}}}
 }
 
+func NewWriterWithDatabase(exec Execer, database string) *Writer {
+	writer := NewWriter(exec)
+	writer.database = normalizeIdentifier(database)
+	return writer
+}
+
 func (w *Writer) EnsureSchema(ctx context.Context, database string) error {
 	for _, statement := range SchemaStatements(database) {
 		if _, err := w.exec.ExecContext(ctx, statement); err != nil {
@@ -59,6 +66,14 @@ func (w *Writer) EnsureSchema(ctx context.Context, database string) error {
 	return nil
 }
 
+func (w *Writer) qualify(table string) string {
+	table = normalizeIdentifier(table)
+	if w.database == "" {
+		return table
+	}
+	return w.database + "." + table
+}
+
 func (w *Writer) AppendAll(ctx context.Context, env envelope.FrameEnvelope) error {
 	if err := w.AppendRawFrame(ctx, env); err != nil {
 		return err
@@ -87,7 +102,7 @@ func (w *Writer) AppendRawFrame(ctx context.Context, env envelope.FrameEnvelope)
 	_, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, frame_id, event_id, message_id, event_time, received_at, raw_size_bytes,
    raw_hex, raw_text, parsed_json, parse_status, parse_error, source_endpoint)
-VALUES (%s)`, table, joinLiterals(rawValues(env, rawHex, rawText, parsedFields))))
+VALUES (%s)`, w.qualify(table), joinLiterals(rawValues(env, rawHex, rawText, parsedFields))))
 	if err != nil {
 		return err
 	}
@@ -103,7 +118,7 @@ VALUES (%s)`, table, joinLiterals(rawValues(env, rawHex, rawText, parsedFields))
 	for _, chunk := range chunks {
 		if _, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, event_id, frame_id, received_at, payload_kind, chunk_index, chunk_count, chunk_text)
-VALUES (%s)`, chunkTable, joinLiterals(chunkValues(env, chunk)))); err != nil {
+VALUES (%s)`, w.qualify(chunkTable), joinLiterals(chunkValues(env, chunk)))); err != nil {
 			return err
 		}
 	}
@@ -144,7 +159,7 @@ func (w *Writer) AppendRawFrameBatch(ctx context.Context, envelopes []envelope.F
 		if _, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, frame_id, event_id, message_id, event_time, received_at, raw_size_bytes,
    raw_hex, raw_text, parsed_json, parse_status, parse_error, source_endpoint)
-VALUES %s`, table, strings.Join(rows, ","))); err != nil {
+VALUES %s`, w.qualify(table), strings.Join(rows, ","))); err != nil {
 			return err
 		}
 	}
@@ -155,7 +170,7 @@ VALUES %s`, table, strings.Join(rows, ","))); err != nil {
 		_ = chunkEnvByTable[table]
 		if _, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, event_id, frame_id, received_at, payload_kind, chunk_index, chunk_count, chunk_text)
-VALUES %s`, table, strings.Join(rows, ","))); err != nil {
+VALUES %s`, w.qualify(table), strings.Join(rows, ","))); err != nil {
 			return err
 		}
 	}
@@ -178,7 +193,7 @@ func (w *Writer) AppendLocation(ctx context.Context, env envelope.FrameEnvelope)
 	_, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, event_id, received_at, longitude, latitude, altitude_m, speed_kmh,
    direction_deg, alarm_flag, status_flag, total_mileage_km)
-VALUES (%s)`, table, joinLiterals(locationValues(env, longitude, latitude))))
+VALUES (%s)`, w.qualify(table), joinLiterals(locationValues(env, longitude, latitude))))
 	return err
 }
 
@@ -206,7 +221,7 @@ func (w *Writer) AppendLocationBatch(ctx context.Context, envelopes []envelope.F
 		if _, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, event_id, received_at, longitude, latitude, altitude_m, speed_kmh,
    direction_deg, alarm_flag, status_flag, total_mileage_km)
-VALUES %s`, table, strings.Join(rows, ","))); err != nil {
+VALUES %s`, w.qualify(table), strings.Join(rows, ","))); err != nil {
 			return err
 		}
 	}
@@ -222,7 +237,7 @@ func (w *Writer) ensureRawChild(ctx context.Context, table string, stable string
 		return nil
 	}
 	statement := fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s USING %s TAGS ('%s', '%s', '%s', '%s', '%s')",
-		table, stable,
+		w.qualify(table), w.qualify(stable),
 		quote(string(env.Protocol)),
 		quote(env.VehicleKey()),
 		quote(env.VIN),
@@ -232,7 +247,7 @@ func (w *Writer) ensureRawChild(ctx context.Context, table string, stable string
 		return err
 	}
 	if phone := normalizePhoneTag(env.Phone); phone != "" {
-		if _, err := w.exec.ExecContext(ctx, fmt.Sprintf("ALTER TABLE %s SET TAG phone = '%s'", table, quote(phone))); err != nil {
+		if _, err := w.exec.ExecContext(ctx, fmt.Sprintf("ALTER TABLE %s SET TAG phone = '%s'", w.qualify(table), quote(phone))); err != nil {
 			return err
 		}
 	}
@@ -250,8 +265,9 @@ func (w *Writer) ensureLocationChild(ctx context.Context, table string, env enve
 	if ok {
 		return nil
 	}
-	statement := fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s USING vehicle_locations TAGS ('%s', '%s')",
-		table,
+	statement := fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s USING %s TAGS ('%s', '%s')",
+		w.qualify(table),
+		w.qualify("vehicle_locations"),
 		quote(string(env.Protocol)),
 		quote(strings.TrimSpace(env.VIN)))
 	if _, err := w.exec.ExecContext(ctx, statement); err != nil {
@@ -367,6 +383,12 @@ func locationTableName(env envelope.FrameEnvelope) string {
 	return "loc_" + strings.ToLower(string(env.Protocol)) + "_" + hash16(strings.TrimSpace(env.VIN))
 }
 
+func normalizeIdentifier(value string) string {
+	value = strings.TrimSpace(value)
+	value = strings.Trim(value, "`")
+	return value
+}
+
 func normalizePhoneTag(phone string) string {
 	trimmed := strings.TrimLeft(strings.TrimSpace(phone), "0")
 	if trimmed == "" {
diff --git a/go/vehicle-gateway/internal/history/writer_test.go b/go/vehicle-gateway/internal/history/writer_test.go
index 150f819c..7e8a6e8f 100644
--- a/go/vehicle-gateway/internal/history/writer_test.go
+++ b/go/vehicle-gateway/internal/history/writer_test.go
@@ -261,6 +261,30 @@ func TestWriterAppendsBatchRowsByChildTable(t *testing.T) {
 	}
 }
 
+func TestWriterWithDatabaseQualifiesTDengineTables(t *testing.T) {
+	exec := &recordingExec{}
+	writer := NewWriterWithDatabase(exec, "vehicle_ts")
+	env := sampleEnvelope()
+
+	if err := writer.AppendAll(context.Background(), env); err != nil {
+		t.Fatalf("AppendAll() error = %v", err)
+	}
+
+	for _, want := range []string{
+		"CREATE TABLE IF NOT EXISTS vehicle_ts.raw_",
+		"USING vehicle_ts.raw_frames",
+		"ALTER TABLE vehicle_ts.raw_",
+		"INSERT INTO vehicle_ts.raw_",
+		"CREATE TABLE IF NOT EXISTS vehicle_ts.loc_",
+		"USING vehicle_ts.vehicle_locations",
+		"INSERT INTO vehicle_ts.loc_",
+	} {
+		if !containsSQL(exec.calls, want) {
+			t.Fatalf("qualified sql missing %q, calls=%v", want, exec.calls)
+		}
+	}
+}
+
 func TestWriterAppendAllBatchSkipsEmptyBatch(t *testing.T) {
 	exec := &recordingExec{}
 	writer := NewWriter(exec)
@@ -338,6 +362,10 @@ func findSQL(calls []execCall, pattern string) string {
 	return ""
 }
 
+func containsSQL(calls []execCall, pattern string) bool {
+	return findSQL(calls, pattern) != ""
+}
+
 func between(value string, start string, end string) string {
 	startIndex := strings.Index(value, start)
 	if startIndex < 0 {