OPTIONS

Configure a Delayed Replica Set Member

To configure a delayed secondary member, set its priority value to 0, its hidden value to true, and its slaveDelay value to the number of seconds to delay.

Important

The length of the secondary slaveDelay must fit within the window of the oplog. If the oplog is shorter than the slaveDelay window, the delayed member cannot successfully replicate operations.

When you configure a delayed member, the delay applies both to replication and to the member’s oplog. For details on delayed members and their uses, see Delayed Replica Set Members.

Example

The following example sets a 1-hour delay on a secondary member currently at the index 0 in the members array. To set the delay, issue the following sequence of operations in a mongo shell connected to the primary:

cfg = rs.conf()
cfg.members[0].priority = 0
cfg.members[0].hidden = true
cfg.members[0].slaveDelay = 3600
rs.reconfig(cfg)

After the replica set reconfigures, the delayed secondary member cannot become primary and is hidden from applications. The slaveDelay value delays both replication and the member’s oplog by 3600 seconds (1 hour).

When updating the replica configuration object, access the replica set members in the members array with the array index. The array index begins with 0. Do not confuse this index value with the value of the _id field in each document in the members array.

Warning

  • The rs.reconfig() shell method can force the current primary to step down, which causes an election. When the primary steps down, the mongod closes all client connections. While this typically takes 10-20 seconds, try to make these changes during scheduled maintenance periods.
  • To successfully reconfigure a replica set, a majority of the members must be accessible. If your replica set has an even number of members, add an arbiter to ensure that members can quickly obtain a majority of votes in an election for primary.