Manage Chained Replication
Starting in version 2.0, MongoDB supports chained replication. A chained replication occurs when a secondary member replicates from another secondary member instead of from the primary. This might be the case, for example, if a secondary selects its replication target based on ping time and if the closest member is another secondary.
Chained replication can reduce load on the primary. But chained replication can also result in increased replication lag, depending on the topology of the network.
You can use the settings.chainingAllowed
setting in Replica Set Configuration to disable chained
replication for situations where chained replication is causing lag.
MongoDB enables chained replication by default. This procedure describes how to disable it and how to re-enable it.
Note
If chained replication is disabled, you still can use
replSetSyncFrom
to specify that a secondary replicates
from another secondary. But that configuration will last only until the
secondary recalculates which member to sync from.
Disable Chained Replication
To disable chained replication, set the
settings.chainingAllowed
field in Replica Set Configuration to false
.
You can use the following sequence of commands to set
settings.chainingAllowed
to
false
:
Copy the configuration settings into the
cfg
object:cfg = rs.config() Take note of whether the current configuration settings contain the
settings
embedded document. If they do, skip this step.Warning
To avoid data loss, skip this step if the configuration settings contain the
settings
embedded document.If the current configuration settings do not contain the
settings
embedded document, create the embedded document by issuing the following command:cfg.settings = { } Issue the following sequence of commands to set
settings.chainingAllowed
tofalse
:cfg.settings.chainingAllowed = false rs.reconfig(cfg)
Re-enable Chained Replication
To re-enable chained replication, set
settings.chainingAllowed
to true
.
You can use the following sequence of commands:
cfg = rs.config() cfg.settings.chainingAllowed = true rs.reconfig(cfg)