This page describes changes and new features introduced in MongoDB Mongosync 1.15.
1.15.0 Release
July 15, 2025
New Features
Pre-Existing Namespaces
Important
This feature is currently in Public Preview. Please review the behavior and limitations in order to use this feature in production environments.
Adds the preExistingDestinationData parameter to the /start API endpoint. If preExistingDestinationData is true,
pre-existing namespaces are allowed on the destination cluster. For more
information, see /start Request Body Parameters.
Warning
If you use this feature with an includeNamespaces filter
and embedded verification enabled, migration can fail with the error “Namespace
filter traversal detected." To avoid this, disable embedded
verification and use an alternative verification method.
Verify Metadata
Starting in version 1.15, the embedded verifier checks for collection metadata,
indexes, and views. If the verifier finds a mismatch during metadata
verification, it returns a map[MismatchType]int error listing the
mismatches. To learn more, see Verification Checks.``
Other Changes
Adds
longRetryTimeas a hidden flag to increasemongosyncresiliency against cluster scaling events. When mongosync's retryer encounters a server selection error with the server topology tagReplicaSetNoPrimary, the retryer bumps its total duration to the value set bylongRetryTime. By default,longRetryTimeis 30 minutes.Adds two log metrics:
Source and destination ping latency
Average source CRUD event rate
Fixed Issues
Fixes an issue where the embedded verifier reported "stream hashing" too early, potentially leading to long cutover times.
Updates
circlpackage to v1.6.0 to resolve a security vulnerability.
Live Upgrades
Live upgrades to 1.15 are not supported.
Minimum Supported Version
For information on minimum supported versions, see MongoDB 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.