> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# Release Notes for mongosync 1.11

This page describes changes and new features introduced in MongoDB Mongosync 1.11.

## 1.11.0 Release

**February 10, 2025**

### Destination-Only Write-Blocking

By default, `mongosync` enables destination-only write-blocking on the destination cluster. `mongosync` unblocks writes right before the [/progress](https://www.mongodb.com/docs/mongosync/current/reference/api/progress.md#std-label-c2c-api-progress) endpoint reports that `canWrite` is `true`. You can explicitly enable destination-only write-blocking by using the [/start](https://www.mongodb.com/docs/mongosync/current/reference/api/start.md#std-label-c2c-api-start) endpoint to set `enableUserWriteBlocking` to `"destinationOnly"`.

You can enable dual write-blocking. If you enable dual write-blocking, `mongosync` blocks writes:

- On the destination cluster during the migration. `mongosync` unblocks writes right before it sets `canWrite` to `true`

- On the source cluster after you call `/commit`

To enable dual write-blocking, use [/start](https://www.mongodb.com/docs/mongosync/current/reference/api/start.md#std-label-c2c-api-start) to set `enableUserWriteBlocking` to `"sourceAndDestination"`.

You can use [/start](https://www.mongodb.com/docs/mongosync/current/reference/api/start.md#std-label-c2c-api-start) to set `enableUserWriteBlocking` to `"none"`.

You cannot enable dual write-blocking or disable write-blocking after the sync starts.

### Live Upgrades

Starting in version 1.11.0, `mongosync` does not support [Live Upgrades.](https://www.mongodb.com/docs/mongosync/current/reference/versioning.md#std-label-c2c-live-upgrade)

### Permissions

`mongosync` requires additional permissions on Atlas destination clusters for default migrations. See [Atlas Clusters.](https://www.mongodb.com/docs/mongosync/current/reference/permissions.md#std-label-c2c-atlas-permissions)

### Other Notes

Fixed Issues:

- Fixed a bug introduced in v1.9.0, where the embedded verifier could incorrectly report a failure if a collection with a TTL index was renamed and later recreated without a TTL index.

- Fixed a bug introduced in v1.0.0 where a `prepareUnique` index could be made unique on the destination collection or a previously unique index could be left in a `prepareUnique` state on the destination collection after cutover.

## Minimum Supported Version

For information on minimum supported versions, see [MongoDB Server Version Compatibility.](https://www.mongodb.com/docs/mongosync/current/reference/supported-server-version.md#std-label-c2c-server-version-compatibility)

For best performance, upgrade your source and destination clusters to the most recent MongoDB Server patch release prior to migration. For more information, see [Upgrade to the Latest Self-Managed Patch Release of MongoDB.](https://www.mongodb.com/docs/manual/tutorial/upgrade-revision.md#std-label-upgrade-to-latest-revision)