In a replicaSet we build a new background index on several collections on the primary.

db.foo.ensureIndex({_pm:1}, {name: 'foo_pm_idx', sparse: true, background: true })

For our smaller collections the index creation on the slave successed. (not sure if this matters)

However on our second biggest collection (the biggest one did succeed) it crashed our secondary.

crash.txt shows the first crash
crash2.txt shows the crash when starting up the secondary again.