diff --git a/packages/backend/server/src/plugins/calendar/__tests__/service.spec.ts b/packages/backend/server/src/plugins/calendar/__tests__/service.spec.ts
index f0a09993c2..9fa7c6bf4e 100644
--- a/packages/backend/server/src/plugins/calendar/__tests__/service.spec.ts
+++ b/packages/backend/server/src/plugins/calendar/__tests__/service.spec.ts
@@ -5,7 +5,11 @@ import test from 'ava';
 
 import { createModule } from '../../../__tests__/create-module';
 import { Mockers } from '../../../__tests__/mocks';
-import { CalendarProviderRequestError, CryptoHelper } from '../../../base';
+import {
+  CalendarProviderRequestError,
+  CryptoHelper,
+  Mutex,
+} from '../../../base';
 import { ConfigModule } from '../../../base/config';
 import { ServerConfigModule } from '../../../core/config';
 import type {
@@ -14,6 +18,7 @@ import type {
 } from '../../../models';
 import { Models } from '../../../models';
 import { CalendarModule } from '../index';
+import { CalendarCronJobs } from '../cron';
 import {
   CalendarProvider,
   CalendarProviderFactory,
@@ -85,8 +90,10 @@ const module = await createModule({
   ],
 });
 const calendarService = module.get(CalendarService);
+const calendarCronJobs = module.get(CalendarCronJobs);
 const providerFactory = module.get(CalendarProviderFactory);
 const models = module.get(Models);
+const mutex = module.get(Mutex);
 module.get(CryptoHelper).onConfigInit();
 
 const createAccount = async (
@@ -599,3 +606,57 @@ test('syncSubscription renews webhook channel when expiring', async t => {
   t.is(updated?.customResourceId, 'new-resource');
   t.truthy(updated?.channelExpiration);
 });
+
+test('pollAccounts skips syncing when cluster lock is unavailable', async t => {
+  mock.method(mutex, 'acquire', async () => undefined);
+  mock.method(
+    models.calendarSubscription,
+    'listAllWithAccountForSync',
+    async () => []
+  );
+  const syncAccountMock = mock.method(calendarService, 'syncAccount', async () => {
+    return;
+  });
+
+  await calendarCronJobs.pollAccounts();
+
+  t.is(syncAccountMock.mock.callCount(), 0);
+});
+
+test('pollAccounts only syncs due accounts', async t => {
+  mock.method(mutex, 'acquire', async () => ({
+    [Symbol.asyncDispose]: async () => {},
+  }));
+  mock.method(
+    models.calendarSubscription,
+    'listAllWithAccountForSync',
+    async () =>
+      [
+        {
+          accountId: 'due-account',
+          lastSyncAt: new Date(Date.now() - 31 * 60 * 1000),
+          account: {
+            refreshIntervalMinutes: 30,
+          },
+        },
+        {
+          accountId: 'fresh-account',
+          lastSyncAt: new Date(Date.now() - 5 * 60 * 1000),
+          account: {
+            refreshIntervalMinutes: 30,
+          },
+        },
+      ] as any
+  );
+
+  const syncAccountMock = mock.method(calendarService, 'syncAccount', async () => {
+    return;
+  });
+
+  await calendarCronJobs.pollAccounts();
+
+  t.deepEqual(
+    syncAccountMock.mock.calls.map(call => call.arguments[0]),
+    ['due-account']
+  );
+});
diff --git a/packages/backend/server/src/plugins/calendar/cron.ts b/packages/backend/server/src/plugins/calendar/cron.ts
index 94c3ad1fd8..b9474a170d 100644
--- a/packages/backend/server/src/plugins/calendar/cron.ts
+++ b/packages/backend/server/src/plugins/calendar/cron.ts
@@ -1,18 +1,27 @@
 import { Injectable } from '@nestjs/common';
 import { Cron, CronExpression } from '@nestjs/schedule';
+import { chunk } from 'lodash-es';
 
+import { Mutex } from '../../base';
 import { Models } from '../../models';
 import { CalendarService } from './service';
 
+const CALENDAR_POLL_LOCK_KEY = 'calendar:poll-accounts';
+const CALENDAR_POLL_BATCH_SIZE = 10;
+
 @Injectable()
 export class CalendarCronJobs {
   constructor(
     private readonly models: Models,
-    private readonly calendar: CalendarService
+    private readonly calendar: CalendarService,
+    private readonly mutex: Mutex
   ) {}
 
   @Cron(CronExpression.EVERY_MINUTE)
   async pollAccounts() {
+    await using lock = await this.mutex.acquire(CALENDAR_POLL_LOCK_KEY);
+    if (!lock) return;
+
     const subscriptions =
       await this.models.calendarSubscription.listAllWithAccountForSync();
 
@@ -46,16 +55,18 @@ export class CalendarCronJobs {
     }
 
     const now = Date.now();
-    await Promise.allSettled(
-      Array.from(accountDueAt.entries()).map(([accountId, info]) => {
-        if (
+    const dueAccountIds = Array.from(accountDueAt.entries())
+      .filter(
+        ([, info]) =>
           !info.lastSyncAt ||
           now - info.lastSyncAt.getTime() >= info.refreshInterval * 60 * 1000
-        ) {
-          return this.calendar.syncAccount(accountId);
-        }
-        return Promise.resolve();
-      })
-    );
+      )
+      .map(([accountId]) => accountId);
+
+    for (const accountIds of chunk(dueAccountIds, CALENDAR_POLL_BATCH_SIZE)) {
+      await Promise.allSettled(
+        accountIds.map(accountId => this.calendar.syncAccount(accountId))
+      );
+    }
   }
 }
diff --git a/packages/backend/server/src/plugins/calendar/service.ts b/packages/backend/server/src/plugins/calendar/service.ts
index dce5877758..0eea2aae20 100644
--- a/packages/backend/server/src/plugins/calendar/service.ts
+++ b/packages/backend/server/src/plugins/calendar/service.ts
@@ -4,6 +4,7 @@ import { Injectable, Logger } from '@nestjs/common';
 import { Transactional } from '@nestjs-cls/transactional';
 import type { CalendarAccount, Prisma } from '@prisma/client';
 import { addDays, subDays } from 'date-fns';
+import { chunk } from 'lodash-es';
 
 import {
   CalendarProviderRequestError,
@@ -32,6 +33,7 @@ const SYNC_FAILURE_BACKOFF_KEY_PREFIX = 'calendar:sync:backoff:';
 const SYNC_FAILURE_BACKOFF_BASE_MS = 5 * 60 * 1000;
 const SYNC_FAILURE_BACKOFF_MAX_MS = 6 * 60 * 60 * 1000;
 const SYNC_FAILURE_BACKOFF_TTL_SECONDS = 24 * 60 * 60;
+const ACCOUNT_SYNC_BATCH_SIZE = 10;
 
 @Injectable()
 export class CalendarService {
@@ -433,11 +435,13 @@ export class CalendarService {
 
     const subscriptions =
       await this.models.calendarSubscription.listByAccountForSync(accountId);
-    await Promise.allSettled(
-      subscriptions.map(subscription =>
-        this.syncSubscription(subscription.id, { reason: 'polling' })
-      )
-    );
+    for (const batch of chunk(subscriptions, ACCOUNT_SYNC_BATCH_SIZE)) {
+      await Promise.allSettled(
+        batch.map(subscription =>
+          this.syncSubscription(subscription.id, { reason: 'polling' })
+        )
+      );
+    }
   }
 
   async listWorkspaceEvents(params: {
diff --git a/packages/backend/server/src/plugins/indexer/__tests__/event.spec.ts b/packages/backend/server/src/plugins/indexer/__tests__/event.spec.ts
index c16f0f25d5..c7139ab346 100644
--- a/packages/backend/server/src/plugins/indexer/__tests__/event.spec.ts
+++ b/packages/backend/server/src/plugins/indexer/__tests__/event.spec.ts
@@ -33,19 +33,37 @@ test('should not index workspace if indexer is disabled', async t => {
   const count = module.queue.count('indexer.indexWorkspace');
 
   // @ts-expect-error ignore missing fields
-  await indexerEvent.indexWorkspace({ id: 'test-workspace' });
+  await indexerEvent.indexWorkspace({
+    workspaceId: 'test-workspace',
+    docId: 'test-workspace',
+  });
 
   t.is(module.queue.count('indexer.indexWorkspace'), count);
 });
 
-test('should index workspace if indexer is enabled', async t => {
+test('should index workspace when root snapshot is updated', async t => {
   // @ts-expect-error ignore missing fields
-  await indexerEvent.indexWorkspace({ id: 'test-workspace' });
+  await indexerEvent.indexWorkspace({
+    workspaceId: 'test-workspace',
+    docId: 'test-workspace',
+  });
 
   const { payload } = await module.queue.waitFor('indexer.indexWorkspace');
   t.is(payload.workspaceId, 'test-workspace');
 });
 
+test('should not index workspace when non-root snapshot is updated', async t => {
+  const count = module.queue.count('indexer.indexWorkspace');
+
+  // @ts-expect-error ignore missing fields
+  await indexerEvent.indexWorkspace({
+    workspaceId: 'test-workspace',
+    docId: 'child-doc',
+  });
+
+  t.is(module.queue.count('indexer.indexWorkspace'), count);
+});
+
 test('should not delete workspace if indexer is disabled', async t => {
   Sinon.stub(config.indexer, 'enabled').value(false);
   const count = module.queue.count('indexer.deleteWorkspace');
diff --git a/packages/backend/server/src/plugins/indexer/event.ts b/packages/backend/server/src/plugins/indexer/event.ts
index 82f9ae1def..1b57085558 100644
--- a/packages/backend/server/src/plugins/indexer/event.ts
+++ b/packages/backend/server/src/plugins/indexer/event.ts
@@ -29,21 +29,20 @@ export class IndexerEvent {
     );
   }
 
-  @OnEvent('workspace.updated')
-  async indexWorkspace({ id }: Events['workspace.updated']) {
+  @OnEvent('doc.snapshot.updated')
+  async indexWorkspace({ workspaceId, docId }: Events['doc.snapshot.updated']) {
     if (!this.config.indexer.enabled) {
       return;
     }
 
+    if (workspaceId !== docId) {
+      return;
+    }
+
     await this.queue.add(
       'indexer.indexWorkspace',
-      {
-        workspaceId: id,
-      },
-      {
-        jobId: `indexWorkspace/${id}`,
-        priority: 100,
-      }
+      { workspaceId },
+      { jobId: `indexWorkspace/${workspaceId}`, priority: 100 }
     );
   }