Oplog Rollover Resilience
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Important
Cluster-to-Cluster Sync Beta Program
This feature is only available in mongosync beta. To learn more,
see Cluster-to-Cluster Sync Beta Program.
Starting in mongosync beta 1.8, you can enable Oplog Rollover
Resilience (ORR). With ORR, mongosync applies changes made on
the source cluster to the destination cluster concurrently with initial sync.
By applying changes earlier in the sync process, mongosync maintains a more
recent position in the oplog. For source clusters with a high write
rate, ORR significantly lowers the risk of oplog rollover during initial sync
and reduces the need to restart the sync.
Syntax
To enable ORR, use --oplogRolloverResilienceIntervalSeconds and specify the
interval, in seconds, in which mongosync checks for eligible change events
in the oplog. The default value is -1, which disables ORR.
For example, to start mongosync with the
oplogRolloverResilienceIntervalSeconds set to 60 seconds, run the
following command:
./bin/mongosync \ --cluster0 "mongodb://localhost:27000" \ --cluster1 "mongodb://localhost:27001" \ --oplogRolloverResilienceIntervalSeconds 60
Behavior
ORR increases the resilience of mongosync to oplog rollover during initial
sync but does not prevent rollover entirely.
You might exceed the oplog window if you:
Sync from a high write rate source cluster for an extended period.
Pause sync for an extended period.
To increase the size of the oplog on the source cluster, use
oplogSizeMB.