Manage Sharded Cluster Balancer
On this page
- Check the Balancer State
- Check if Balancer is Running
- Configure Default Chunk Size
- Schedule the Balancing Window
- Remove a Balancing Window Schedule
- Disable the Balancer
- Enable the Balancer
- Disable Balancing During Backups
- Disable Balancing on a Collection
- Enable Balancing on a Collection
- Confirm Balancing is Enabled or Disabled
- Change Replication Behavior for Chunk Migration
- Change the Maximum Storage Size for a Given Shard
Changed in version 3.4: The balancer process has moved from the
mongos instances to the primary member of the config server replica set.
This page describes common administrative procedures related to balancing. For an introduction to balancing, see Sharded Cluster Balancer. For lower level information on balancing, see Cluster Balancer.
To see if the balancer is enabled in your sharded cluster, issue the following command, which returns a boolean:
To see if the balancer process is active in your cluster:
The default chunk size for a sharded cluster is 64 megabytes. In most situations, the default size is appropriate for splitting and migrating chunks. For information on how chunk size affects deployments, see details, see Chunk Size.
Changing the default chunk size affects chunks that are processes during migrations and auto-splits but does not retroactively affect all chunks.
To configure default chunk size, see Modify Chunk Size in a Sharded Cluster.
In some situations, particularly when your data set grows slowly and a migration can impact performance, it is useful to ensure that the balancer is active only at certain times. The following procedure specifies the
activeWindow, which is the timeframe during which the balancer will be able to migrate chunks:
Switch to the Config Database.
Issue the following command to switch to the config database.
The balancer will not activate in the
stopped state. To ensure that the balancer is not
sh.setBalancerState(), as in the following:
The balancer will not start if you are outside of the
update(), as in the following:
<end-time> with time values using two digit hour and minute values (i.e.
HH:MM) that specify the beginning and end boundaries of the balancing window.
HHvalues, use hour values ranging from
MMvalue, use minute values ranging from
MongoDB evaluates the start and stop times relative to the time zone of the member which is serving as a primary in the config server replica set.
The balancer window must be sufficient to complete the migration of all data inserted during the day.
As data insert rates can change based on activity and usage patterns, it is important to ensure that the balancing window you select will be sufficient to support the needs of your deployment.
Do not use the
sh.startBalancer() method when you have set an
By default, the balancer may run at any time and only moves chunks as needed. To disable the balancer for a short period of time and prevent all migration, use the following procedure:
Issue the following operation to disable the balancer:
If a migration is in progress, the system will complete the in-progress migration before stopping.
To verify that the balancer will not start, issue the following command, which returns
falseif the balancer is disabled:
Optionally, to verify no migrations are in progress after disabling, issue the following operation in the
To disable the balancer from a driver, use the balancerStop command against the
admin database, as in the following:
Use this procedure if you have disabled the balancer and are ready to re-enable it: