fix(metrics): enhance metrics dashboard layout and optimize database queries

- Increased the bottom margin of charts in the metrics dashboard for improved visual spacing.
- Added titles to the charts for better context and understanding of displayed data.
- Introduced composite indexes in the database to optimize aggregation queries and improve performance.
- Modified the SQL query in GetRecentMetrics to calculate incremental changes in metrics, enhancing data accuracy and usability.

These changes improve the user experience by providing clearer visualizations and more efficient data retrieval in the metrics dashboard.

internal/handler/metrics.go

@@ -318,7 +318,7 @@ var metricsTemplate = `
         }
         .chart {
             height: 200px;
-            margin-bottom: 20px;
+            margin-bottom: 50px;
         }
         #timeRange {
             padding: 8px;
@@ -488,12 +488,15 @@ var metricsTemplate = `
         <div id="historyChart">
             <div class="chart-container">
                 <div class="chart">
+                    <h3 style="text-align:center">请求数</h3>
                     <canvas id="requestsChart"></canvas>
                 </div>
                 <div class="chart">
+                    <h3 style="text-align:center">错误率%</h3>
                     <canvas id="errorRateChart"></canvas>
                 </div>
                 <div class="chart">
+                    <h3 style="text-align:center">流量MB</h3>
                     <canvas id="bytesChart"></canvas>
                 </div>
             </div>

internal/models/metrics.go

@@ -113,6 +113,29 @@ func initTables(db *sql.DB) error {
 		CREATE INDEX IF NOT EXISTS idx_metrics_timestamp ON metrics_history(timestamp);
 		CREATE INDEX IF NOT EXISTS idx_status_timestamp ON status_stats(timestamp);
 		CREATE INDEX IF NOT EXISTS idx_path_timestamp ON path_stats(timestamp);
+
+		-- 复合索引，用于优化聚合查询
+		CREATE INDEX IF NOT EXISTS idx_metrics_timestamp_values ON metrics_history(
+			timestamp,
+			total_requests,
+			total_errors,
+			total_bytes,
+			avg_latency
+		);
+
+		-- 路径统计的复合索引
+		CREATE INDEX IF NOT EXISTS idx_path_stats_composite ON path_stats(
+			timestamp,
+			path,
+			requests
+		);
+
+		-- 状态码统计的复合索引
+		CREATE INDEX IF NOT EXISTS idx_status_stats_composite ON status_stats(
+			timestamp,
+			status_group,
+			count
+		);
 	`)
 	if err != nil {
 		return err
@@ -240,7 +263,7 @@ func (db *MetricsDB) GetRecentMetrics(hours int) ([]HistoricalMetrics, error) {
 		interval = "%Y-%m-%d 00:00:00"
 	}
 
-	// 修改查询，使用 localtime 修饰符
+	// 修改查询，计算每个时间段的增量
 	rows, err := db.DB.Query(`
 		WITH grouped_metrics AS (
 			SELECT 
@@ -248,13 +271,22 @@ func (db *MetricsDB) GetRecentMetrics(hours int) ([]HistoricalMetrics, error) {
 				SUM(total_requests) as total_requests,
 				SUM(total_errors) as total_errors,
 				SUM(total_bytes) as total_bytes,
-				CAST(AVG(CAST(avg_latency AS FLOAT)) AS FLOAT) as avg_latency
+				CAST(AVG(CAST(avg_latency AS FLOAT)) AS FLOAT) as avg_latency,
+				LAG(SUM(total_requests)) OVER (ORDER BY strftime(?1, timestamp, 'localtime')) as prev_requests,
+				LAG(SUM(total_errors)) OVER (ORDER BY strftime(?1, timestamp, 'localtime')) as prev_errors,
+				LAG(SUM(total_bytes)) OVER (ORDER BY strftime(?1, timestamp, 'localtime')) as prev_bytes
 			FROM metrics_history
 			WHERE timestamp >= datetime('now', '-' || ?2 || ' hours', 'localtime')
 				GROUP BY group_time
 			ORDER BY group_time DESC
 		)
-		SELECT * FROM grouped_metrics
+		SELECT 
+			group_time as timestamp,
+			COALESCE(total_requests - prev_requests, total_requests) as total_requests,
+			COALESCE(total_errors - prev_errors, total_errors) as total_errors,
+			COALESCE(total_bytes - prev_bytes, total_bytes) as total_bytes,
+			avg_latency
+		FROM grouped_metrics
 	`, interval, hours)
 	if err != nil {
 		return nil, err