Mastering MongoDB 4.x - Second Edition

Delayed replica set members

In many cases, we will want to have a node that holds a copy of our data at an earlier point in time. This helps to recover from a big subset of human errors, like accidentally dropping a collection, or an upgrade going horrendously wrong.

A delayed replica set member has to be priority = 0 and hidden = true. A delayed replica set member can vote for elections, but will never be visible to clients (hidden = true) and will never become a primary (priority = 0).

An example is as follows:

> cfg = rs.conf()> cfg.members[0].priority = 0> cfg.members[0].hidden = true> cfg.members[0].slaveDelay = 7200> rs.reconfig(cfg)

This will set the members[0] to a delay of 2 hours. Two important factors for deciding the delta ...