AlwaysOn & Redo Thread & RollBack Command

Hi,

I have 3 replicas configured in Availability groups with 2 read_only secondary replicas-availability mode-Sync Commit.

I have 1 transaction running for last 4 hrs(insert command) but not committed, will they be visible on secondary Replicas?

If i rollback, How redo thread will do undo as this is only for Redo phase.

Or how redo thread runs Undo phase while replaying records.

Regards

Manish