On this page
mongosyncrun on its own hardware?
- Should I increase the size of the
oplogin the source cluster?
- Which connection string options does
- Which security and authentication options are supported?
- Can I configure
mongosyncfor high availability?
- Can the source or destination be a replica set with arbiters?
- What if I see a Slow Operation Warning?
This page provides answers to some frequently asked questions we have encountered. If you have additional questions please contact MongoDB Support.
mongosync can run on its own hardware.
mongosync does not
have to run on the servers that host your MongoDB instances. When
mongosync runs on its own hardware, it can use an operating system
(OS) that is different than the OS on the source or destination
The oplog is a capped collection that keeps a rolling record of all operations that modify the data stored in your databases.
mongosync applies operations in the
oplog on the source cluster
to the data on the destination cluster. When operations
mongosync has not applied roll off the
on the source cluster, the sync fails and
During the initial sync,
mongosync may apply operations at a slower
rate due to the load imposed by copying documents concurrently.
mongosync completes the initial sync, it applies changes
faster and is more likely to maintain a position in the
that is close to the real-time writes occuring on the source cluster.
If you anticipate syncing a large data set, or if you plan to pause
synchronization for an extended period of time, you might exceed the
oplog window. Use the
to increase the size of the
oplog on the source cluster.
To learn more about how to increase the size of the
Change the Size of the Oplog.
readConcern is not
mongosync returns an
Invalid URI option, read concern must be majority
writeConcern is not
mongosync returns an
Invalid URI option, write concern must be majority
mongosync accepts all other connection string options.
mongosync uses a standard MongoDB connection string to connect to the source and destination clusters.
There is no automatic failover built into
mongosync. However you
can write a script or use your operating system's process managers,
systemd for example, to restart the
mongosync binary is stateless. The metadata for restarting is
stored on the destination cluster.
mongosync operation can be resumed if
unavailable during synchronization. When
available again, restart the
mongosync process with the same
mongosync resumes the operation from where it stopped
mongosync became unavailable.
Yes, the replica set can have arbiters. The source replica set must have more than 2 non-arbiter nodes and you must sync from a non-arbiter node. Use the source cluster's connection string to specify a read preference for a non-arbiter, data-bearing node.
Slow operation warnings can occur during the initial sync or the application of a change event when there is a slow read operation on the source cluster or a slow write operation on the destination cluster. The warning may indicate network congestion or resource strain on the source or destination cluster.
While these warnings do not indicate failures in themselves, slow operations
can cause operation timeout errors in
mongosync and migration failures.
If you see slow operation warnings, check CPU, memory, and network usage on the source and destination clusters. If the clusters are underprovisioned for your needs, consider upgrading the cluster hardware.