diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index 95a394a43..149123e2c 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -990,17 +990,15 @@ export class ProblemPrefixListHandler extends Handler {
     @param('prefix', Types.Name)
     async get(domainId: string, prefix: string) {
         const pdocs = await problem.getPrefixList(domainId, prefix);
-        if (!Number.isNaN(+prefix)) {
+        if (!Number.isNaN(+prefix) && !pdocs.filter((i) => i.docId === +prefix)) {
             const pdoc = await problem.get(domainId, +prefix, ['domainId', 'docId', 'pid', 'title']);
             if (pdoc) pdocs.unshift(pdoc);
         }
-        const search = global.Hydro.lib.problemSearch;
         if (pdocs.length < 20) {
-            if (search) {
-                const result = await search(domainId, prefix, { limit: 20 - pdocs.length });
-                const docs = await problem.getMulti(domainId, { docId: { $in: result.hits.map((i) => +i.split('/')[1]) } }).toArray();
-                pdocs.push(...docs);
-            }
+            const search = global.Hydro.lib.problemSearch || defaultSearch;
+            const result = await search(domainId, prefix, { limit: 20 - pdocs.length });
+            const docs = await problem.getMulti(domainId, { docId: { $in: result.hits.map((i) => +i.split('/')[1]) } }).toArray();
+            pdocs.push(...docs);
         }
         this.response.body = pdocs;
     }
diff --git a/packages/hydrooj/src/loader.ts b/packages/hydrooj/src/loader.ts
index edfff0c01..922d6ba1b 100644
--- a/packages/hydrooj/src/loader.ts
+++ b/packages/hydrooj/src/loader.ts
@@ -70,7 +70,7 @@ export async function load() {
     addon(path.resolve(__dirname, '..'), true);
     Error.stackTraceLimit = 50;
     require('./entry/worker').load();
-    if (global.gc) global.gc();
+    global.gc?.();
 }
 
 export async function loadCli() {
diff --git a/packages/hydrooj/src/model/problem.ts b/packages/hydrooj/src/model/problem.ts
index 90001aa35..282129c26 100644
--- a/packages/hydrooj/src/model/problem.ts
+++ b/packages/hydrooj/src/model/problem.ts
@@ -340,7 +340,8 @@ export class ProblemModel {
         prefix = prefix.toLowerCase();
         const $regex = new RegExp(`\\A${escapeRegExp(prefix)}`, 'gmi');
         const filter = { $or: [{ pid: { $regex } }, { title: { $regex } }] };
-        return await document.getMulti(domainId, document.TYPE_PROBLEM, filter, ['domainId', 'docId', 'pid', 'title']).toArray();
+        return await document.getMulti(domainId, document.TYPE_PROBLEM, filter, ['domainId', 'docId', 'pid', 'title'])
+            .limit(20).toArray();
     }
 
     static async getListStatus(domainId: string, uid: number, pids: number[]) {
diff --git a/packages/hydrooj/src/ui.ts b/packages/hydrooj/src/ui.ts
index c7609da21..3a29c5225 100644
--- a/packages/hydrooj/src/ui.ts
+++ b/packages/hydrooj/src/ui.ts
@@ -33,7 +33,7 @@ async function executeCommand(input: string) {
 }
 
 process.stdin.setEncoding('utf-8');
-if (process.stdin.setRawMode) process.stdin.setRawMode(false);
+process.stdin.setRawMode?.(false);
 process.stdin.on('data', (buf) => {
     const input = buf.toString();
     executeCommand(input);
diff --git a/packages/hydrooj/src/upgrade.ts b/packages/hydrooj/src/upgrade.ts
index 9b3e13b5e..9e83bdc72 100644
--- a/packages/hydrooj/src/upgrade.ts
+++ b/packages/hydrooj/src/upgrade.ts
@@ -842,6 +842,11 @@ const scripts: UpgradeScript[] = [
         }
         return true;
     },
+    async function _68_69() {
+        const _FRESH_INSTALL_IGNORE = 1;
+        await db.collection('cache' as any).deleteMany({});
+        return true;
+    },
 ];
 
 export default scripts;