feat(migration): 添加 flow_run_logs 复合索引并修复 flow_id 类型

优化 flow_run_logs 查询性能，添加常用排序和过滤的复合索引
将 flow_id 从 VARCHAR(64) 改为 BIGINT 以匹配实体模型
在分页查询中实现末页优化策略

backend/src/services/flow_run_log_service.rs

@@ -1,5 +1,6 @@
 use crate::{db::Db, models::flow_run_log};
 use sea_orm::{ActiveModelTrait, Set, EntityTrait, PaginatorTrait, QueryFilter, QueryOrder, ColumnTrait};
+use sea_orm::QuerySelect;
 use chrono::{DateTime, FixedOffset, Utc};
 
 #[derive(serde::Serialize)]
@@ -61,18 +62,71 @@ pub async fn create(db: &Db, input: CreateRunLogInput) -> anyhow::Result<i64> {
     Ok(m.id)
 }
 
+
+/// 分页查询流程运行日志
+/// 
+/// # 参数
+/// * `db` - 数据库连接
+/// * `p` - 查询参数，包含页码、每页大小、流程ID、流程代码、用户名、运行状态等过滤条件
+/// 
+/// # 返回值
+/// * `Ok(PageResp<RunLogItem>)` - 分页查询结果，包含日志列表和分页信息
+/// * `Err(anyhow::Error)` - 查询失败的错误信息
 pub async fn list(db: &Db, p: ListParams) -> anyhow::Result<PageResp<RunLogItem>> {
-    let page = p.page.unwrap_or(1); let page_size = p.page_size.unwrap_or(10);
-    let mut selector = flow_run_log::Entity::find();
-    if let Some(fid) = p.flow_id { selector = selector.filter(flow_run_log::Column::FlowId.eq(fid)); }
-    if let Some(fcode) = p.flow_code { selector = selector.filter(flow_run_log::Column::FlowCode.eq(fcode)); }
-    if let Some(u) = p.user {
-        let like = format!("%{}%", u);
-        selector = selector.filter(flow_run_log::Column::Username.like(like));
+    let page = p.page.unwrap_or(1).max(1);
+    let page_size = p.page_size.unwrap_or(10).max(1);
+
+    // 公用查询条件
+    let mut base_selector = flow_run_log::Entity::find();
+    if let Some(fid) = p.flow_id {
+        base_selector = base_selector.filter(flow_run_log::Column::FlowId.eq(fid));
     }
-    if let Some(ok) = p.ok { selector = selector.filter(flow_run_log::Column::Ok.eq(ok)); }
-    let paginator = selector.order_by_desc(flow_run_log::Column::Id).paginate(db, page_size);
-    let total = paginator.num_items().await? as u64;
-    let models = paginator.fetch_page(if page>0 { page-1 } else { 0 }).await?;
-    Ok(PageResp { items: models.into_iter().map(Into::into).collect(), total, page, page_size })
+    if let Some(fcode) = p.flow_code.as_ref() {
+        base_selector = base_selector.filter(flow_run_log::Column::FlowCode.eq(fcode.clone()));
+    }
+    if let Some(u) = p.user.as_ref() {
+        let like = format!("%{}%", u.replace('%', "\\%").replace('_', "\\_"));
+        base_selector = base_selector.filter(flow_run_log::Column::Username.like(like));
+    }
+    if let Some(ok) = p.ok {
+        base_selector = base_selector.filter(flow_run_log::Column::Ok.eq(ok));
+    }
+
+    // 总数只查一次，保持和老接口兼容
+    let total = base_selector.clone().count(db).await? as u64;
+
+    // 计算偏移量
+    let offset = (page - 1) * page_size;
+
+    // ⭐ 关键优化：判断前半区 / 后半区
+    let models = if offset > total / 2 {
+        // ---- 末页优化：用升序 + limit + reverse ----
+        let start_idx = total.saturating_sub(page * page_size);
+        let asc_selector = base_selector.clone();
+        let mut rows = asc_selector
+            .order_by_asc(flow_run_log::Column::StartedAt)
+            .order_by_asc(flow_run_log::Column::Id)
+            .offset(start_idx)
+            .limit(page_size)
+            .all(db)
+            .await?;
+        rows.reverse();
+        rows
+    } else {
+        // ---- 常规分页 ----
+        base_selector
+            .order_by_desc(flow_run_log::Column::StartedAt)
+            .order_by_desc(flow_run_log::Column::Id)
+            .offset(offset)
+            .limit(page_size)
+            .all(db)
+            .await?
+    };
+
+    Ok(PageResp {
+        items: models.into_iter().map(Into::into).collect(),
+        total,
+        page,
+        page_size,
+    })
 }