diff --git a/apps/api/src/routes/account.ts b/apps/api/src/routes/account.ts
index 8f91b44..443f27e 100644
--- a/apps/api/src/routes/account.ts
+++ b/apps/api/src/routes/account.ts
@@ -181,23 +181,27 @@ accountRoutes.get("/rankings/users", optionalAuth, async (c) => {
   const limit = queryInteger(c.req.query("limit"), 10, { min: 1, max: LEADERBOARD_SIZE })
   const offset = queryInteger(c.req.query("offset"), 0, { min: 0 })
 
-  const [totalRow] = await db.select({ value: count() }).from(schema.userProfile)
-    .innerJoin(schema.user, eq(schema.userProfile.userId, schema.user.id))
-    .where(leaderboardWhere)
-  const total = Math.min(totalRow?.value ?? 0, LEADERBOARD_SIZE)
+  // 榜单封顶 100 名，所以这一页最多还能取几条只取决于 offset，**不取决于总人数** ——
+  // 真人不够时数据库自己会少返回。不拿 total 当上限，三段查询就能并发发出去，
+  // 端点延迟从「四个来回相加」变成「最慢的那个」。越界页一条不剩，直接不发 SQL。
+  const pageLimit = Math.max(0, Math.min(limit, LEADERBOARD_SIZE - offset))
 
-  // 末页可能只剩不足 limit 条，越界页一条不剩 —— 后者直接不发 SQL
-  const pageLimit = Math.max(0, Math.min(limit, total - offset))
-  const rows = pageLimit === 0 ? [] : await db
-    .select({ profile: schema.userProfile, user: schema.user }).from(schema.userProfile)
-    .innerJoin(schema.user, eq(schema.userProfile.userId, schema.user.id))
-    .where(leaderboardWhere).orderBy(...leaderboardOrder)
-    .limit(pageLimit).offset(offset)
+  const [totalRow, rows, me] = await Promise.all([
+    db.select({ value: count() }).from(schema.userProfile)
+      .innerJoin(schema.user, eq(schema.userProfile.userId, schema.user.id))
+      .where(leaderboardWhere).then(([row]) => row),
+    pageLimit === 0 ? [] : db
+      .select({ profile: schema.userProfile, user: schema.user }).from(schema.userProfile)
+      .innerJoin(schema.user, eq(schema.userProfile.userId, schema.user.id))
+      .where(leaderboardWhere).orderBy(...leaderboardOrder)
+      .limit(pageLimit).offset(offset),
+    myLeaderboardRank(c.get("user")?.id),
+  ])
 
   return success(c, userRankSchema.parse({
     results: rows.map(serializeRankRow),
-    total,
-    me: await myLeaderboardRank(c.get("user")?.id),
+    total: Math.min(totalRow?.value ?? 0, LEADERBOARD_SIZE),
+    me,
   }))
 })
 
diff --git a/apps/api/src/routes/classroom.ts b/apps/api/src/routes/classroom.ts
index f40ba7b..642d629 100644
--- a/apps/api/src/routes/classroom.ts
+++ b/apps/api/src/routes/classroom.ts
@@ -5,7 +5,7 @@ import {
   classRankItemSchema,
   classUserRankSchema,
 } from "@oj2/contract"
-import { and, asc, eq, gte, inArray, lte, sql } from "drizzle-orm"
+import { and, eq, gte, inArray, like, lte, sql } from "drizzle-orm"
 import { Hono } from "hono"
 
 import { requireAuth, type AppEnv } from "../auth/middleware"
@@ -24,13 +24,19 @@ interface ClassUser {
   submissionNumber: number
 }
 
-async function loadClassUsers(classNames?: string[]) {
+/**
+ * 入班学生的 AC/提交数。`gradePrefix` 是年级（班号形如 `241` = 24 级 1 班），
+ * 走 SQL 的 like 而不是拉全表再在内存里 startsWith —— 班级榜每换一次年级就要跑一遍，
+ * 没必要每次都把全校一千多号人搬进进程。年级在调用处已校验为纯数字，不含 like 通配符。
+ */
+async function loadClassUsers(classNames?: string[], gradePrefix?: string) {
   const filters = [
     eq(schema.user.isDisabled, false),
     inArray(schema.user.adminType, ["Regular User", "Student Admin"]),
     sql`${schema.user.className} is not null`,
   ]
   if (classNames) filters.push(inArray(schema.user.className, classNames))
+  if (gradePrefix) filters.push(like(schema.user.className, `${gradePrefix}%`))
   const rows = await db.select({
     userId: schema.user.id,
     username: schema.user.username,
@@ -72,7 +78,7 @@ function sampleStdDev(values: number[]) {
 classroomRoutes.get("/rankings/classes", async (c) => {
   const grade = c.req.query("grade")?.trim()
   if (!grade || !/^\d+$/.test(grade)) return failure(c, 400, "invalid-grade", "grade is required")
-  const users = (await loadClassUsers()).filter((user) => user.className.startsWith(grade))
+  const users = await loadClassUsers(undefined, grade)
   const groups = new Map<string, ClassUser[]>()
   for (const user of users) groups.set(user.className, [...(groups.get(user.className) ?? []), user])
   const result = [...groups].map(([className, members]) => {
diff --git a/apps/web/src/oj/rank/list.vue b/apps/web/src/oj/rank/list.vue
index 020ebe5..1981133 100644
--- a/apps/web/src/oj/rank/list.vue
+++ b/apps/web/src/oj/rank/list.vue
@@ -242,11 +242,13 @@ const columns: DataTableColumn<Rank>[] = [
 ]
 
 watch(() => query.page, init)
+// 改每页条数时，若当前不在第一页，把重新取数交给 page 的 watcher ——
+// 这里再自己取一次，就是两个一模一样的请求
 watch(
   () => query.limit,
   () => {
-    query.page = 1
-    init()
+    if (query.page === 1) init()
+    else query.page = 1
   },
 )
 watch(duration, listActivity)
@@ -265,12 +267,6 @@ async function listActivity() {
   }))
 }
 
-// 「全服 Top10」就是同一个榜的第一页 —— 上限由服务端定，这里只要前 10 条
-async function listRank() {
-  const res = await getRank(0, 10)
-  rankChart.value = res.results
-}
-
 const options: SelectOption[] = [
   { label: "一周内", value: "weeks:1" },
   { label: "一个月内", value: "months:1" },
@@ -288,8 +284,10 @@ const subOptions = computed<Duration>(() => {
 })
 
 onMounted(() => {
-  init()
-  listRank()
+  // 「全服 Top10」就是榜单第一页的前 10 条：挂载时 init() 取的正是 offset=0&limit=10，
+  // 再单发一次一模一样的 /rankings/users 只会让这张图排在日活后面出来。
+  // 图只在挂载时定一次，翻页/改每页条数不该动它。
+  init().then((results) => (rankChart.value = results.slice(0, 10)))
   listActivity()
   listClassRank()
   listMyClassRank()
@@ -480,13 +478,12 @@ watch(
   },
 )
 
+// 同上：page 改了自会触发下面那个 watcher，别重复取
 watch(
   () => myClassQuery.limit,
   () => {
-    myClassQuery.page = 1
-    if (myClassScope.value === "all") {
-      listMyClassRank()
-    }
+    if (myClassQuery.page !== 1) myClassQuery.page = 1
+    else if (myClassScope.value === "all") listMyClassRank()
   },
 )
 </script>