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Percona Software for MongoDB Documentation

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Known issues and limitations

This page lists known limitations for using Percona ClusterSync for MongoDB.

Versions and topology

  • MongoDB versions that reached End-of-Life are not supported
  • PCSM connects only to the primary node in the replica set. You cannot force connection to secondary members using the directConnection option. This option is ignored.

Cross-version replication

  • Feature Compatibility Version (FCV) is not automatically checked between your source and target clusters

    PCSM does not automatically check the Feature Compatibility Version (FCV) between your source and target clusters. Because an incompatible FCV might cause replication failures, it is important to perform this check manually before you begin:

    Confirm the FCV for both your source and target clusters. Ensure the target cluster’s FCV is equal to or higher than the source cluster’s FCV.

  • Downgrade replication is not supported

    PCSM blocks startup if the source major version is higher than the target major version.

Sharded clusters

The following limitations apply specifically to sharded cluster replication:

  • PCSM replicates the data and doesn’t replicate metadata. This means that the following information is not preserved from the source cluster:

  • The primary shard name for a collection. The target cluster may have a different primary shard name.

  • The chunk distribution information. The target cluster manages chunk distribution according to its own sharding configuration. See Sharding support for more information.

  • The configuration of zones for sharded data .

  • During data replication, the following commands are not supported: movePrimary, reshardCollecton, unshardCollection, refineCollectionShardKey. Running them results in failed replication and you must start it anew, from the initial data sync stage.

Data types

  • Queryable encryption is not supported
  • Users and roles are not synchronized
  • Timeseries collections are not supported
  • system.* collections are not replicated
  • Clustered collections with indexes that have the expireAfterSeconds field defined are not supported because the change stream does not provide a Time-to-Live (TTL) value for the index
  • Capped collections created or converted as the result of cloneCollectionAsCapped and convertToCapped commands are not supported. These operations don’t change the event and are not captured by the change streams.
  • Percona Memory Engine is not supported
  • Persistent Query Settings (added in MongoDB 8) are not supported
  • Documents that have field names with periods and dollar signs are not supported

Other

The following functionalities are not supported:

  • Multiple source or multiple target clusters
  • You cannot resume initial synchronization if an issue occurred. You must start it from scratch.
  • Arbitrary database upgrades during a sync are not supported. For supported staged upgrades from lower to higher MongoDB major versions, follow the cross-version replication procedure.
  • Reverse synchronization
  • External authentication via Kerberos, AWS and LDAP
Last update: June 17, 2026
Created: June 17, 2026