‘mongod replication lag’
Investigating the problem
There is a fabric task to show various mongo replication status information.:
fab <environment> -H mongo-?.backend mongo.status
db.printReplicationInfo()section shows where the primary node’s oplog is up to.
db.printSlaveReplicationInfo()section shows where each secondary is synced to and how far behind the master it is.
rs.status()section shows the current status of each node and the last heartbeat error message for the secondaries.
Try restarting one of the lagging mongod secondaries:
fab <environment> -H mongo-?.backend app.restart:mongodb
This may restart replication on that node, and also cause the other lagging node to resync with the primary node and restart its own replication.
If restarting doesn’t solve the problem force a resync with fabric:
fab <environment> -H mongo-?.backend mongo.force_resync