I have a question about step down. The release notes for mongo 2.0 (we are running 2.4.6) state,

‘To minimize time without a primary, the rs.stepDown() method will now fail if the primary does not see asecondary within 10 seconds of its latest optime. You can force the primary to step down anyway, but by default it will return an error message.’ (http://docs.mongodb.org/manual/release-notes/2.0/)

Lets take the following example;

There are 2 data nodes, nodeA & nodeB, nodeA is the primary, nodeB is the secondary and is 9 seconds behind. The replica set is told to step down, nodeA becomes secondary, and nodeB elects itself as primary.

What I am interested in is, what happens to the 9 seconds worth of data that the primary had when it was in front and told to step down? Is that data 'lost' in a rollback, ie. http://docs.mongodb.org/manual/core/replica-set-rollbacks/ ??