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mongosync does not check for compliance with the documented
limitations. Please ensure that your application is not affected by
the limitations. Running
mongosync in the presence of one of
these limitations could lead to undefined behavior on the destination
For information on MongoDB server compatility, see MongoDB Server Version Compatibility and Support.
The destination cluster must be empty.
mongosyncdoesn't validate that the clusters or the environment are properly configured.
Other clients must not write to the destination cluster while
If write blocking is disabled, the client must prevent writes to the source cluster before starting the commit process.
applyOpsoperations from the source cluster aren't supported.
system.* collections aren't replicated.
Documents that have dollar (
$) prefixed field names aren't supported. See Field Names with Periods and Dollar Signs.
Serverless clusters aren't supported.
A MongoDB Shared Tier isn't supported.
Queryable Encryption isn't supported.
You cannot sync a collection that has a unique index and a non-unique index defined on the same field(s).
Before you attempt to run
M10+Atlas cluster, disable the Require Indexes for All Queries option.
mongosyncdoesn't sync users or roles.
MongoDB does not test Cluster-to-Cluster Sync with Community builds and in most cases, MongoDB does not offer support for Cluster-to-Cluster Sync with Community deployments. If you would like to use Cluster-to-Cluster Sync with MongoDB Community Edition, contact a MongoDB sales representative to discuss requirements and individualized options.
Time-series collections aren't supported.
Clustered collections with expireAfterSeconds set aren't supported.
mongosyncdoesn't support sync from a sharded cluster to a replica set.
Sync from a replica set to a sharded cluster has the following limitations:
mongosyncallows users to rename collections that the
sharding.shardingEntriesoption for the
startcommand includes during sync. To see limitations on renaming collections while
mongosyncis running, see Renaming During Sync.
When using the
sharding.createSupportingIndexesoption to create indexes supporting shard keys on the destination cluster during sync, you cannot create these indexes afterwards on the source cluster.
The index must either exist before
mongosyncstarts or be created after the migration is complete and
Within a collection, the
_idfield must be unique across all of the shards in the cluster. See Sharded Clusters and Unique Indexes for more details.
movePrimarycommand cannot be used to reassign the primary shard while syncing.
There is no replication for zone configuration.
mongosyncreplicates data, it doesn't inherit zones.
Shards cannot be added or removed while syncing.
mongosynconly syncs indexes that exist on all shards.
mongosynconly syncs indexes that have consistent index specifications on all shards.
To check for index inconsistencies, see Find Inconsistent Indexes Across Shards.
The shard key cannot be refined while syncing.
The shard key cannot be modified using
The maximum number of indexes per sharded collection is 63, which is one less than the default limit of 64.
mongosynconly supports syncing sharded collections that have default collation settings.
If the old source has unique indexes which are partially distributed across shards, reversing may cause failures. Ensure that unique indexes exist on all shards before reversing.
The source and destination clusters must have the same number of shards. You cannot reverse sync when the clusters have different topologies or major versions.
Syncing multiple source clusters to one destination cluster isn't supported.
Syncing one source cluster to many destination clusters isn't supported.
Filtering is not supported with reversible sync.
The destination cluster must not contain user data prior to starting.
The destination cluster must not contain the
mongosync_reserved_for_internal_usesystem database prior to starting.
You cannot modify a filter that is in use. To create a new filter, see: Replace an Existing Filter.
You can only rename collections in certain situations. For more details see: Adding and Renaming Collections.
If a filter includes a view but not the base collection, only the view is replicated.
You cannot specify system collections or system databases in a filter.
To use the
$outaggregation stage or the
mapReducecommand (when set to create or replace a collection) with filtering, you must configure the filter to use the entire database. You cannot limit the filter to collections within the database.
For more information, see Filtering with mapReduce and $out.
Starting in 1.3.0, Cluster-to-Cluster Sync supports capped collections with some limitations.
convertToCappedis not supported. If you run
mongosyncexits with an error.
cloneCollectionAsCappedis not supported.
Capped collections on the source cluster work normally during sync.
Capped collections on the destination cluster have temporary changes during sync:
There is no maximum number of documents.
The maximum collection size is 1PB.
mongosync restores the original values for maximum number of
documents and maximum document size during commit.
Cluster-to-Cluster Sync does not replicate system collections to the destination cluster.
If you issue a
dropDatabase command on the source cluster,
this change is not directly applied on the destination cluster. Instead,
Cluster-to-Cluster Sync drops user collections and views in the database
on the destination cluster, but it does not drop system collections
on that database.
For example, on the destination cluster:
The drop operation does not affect a user-created
If you enable profiling, the
If you create views on the source cluster and then drop the database, replicating the drop removes the views, but leaves an empty
In these cases, the replication of
dropDatabase removes all user-created
collections from the database, but leaves its system collections on the