Anybody knows difference between redo log files and undo tablespace.

Its fucking confusing.

No :(

Apparently most of people don't. Its surprising that apart from the official documentation, which is really hard to understand, there is no other trusted source of tutorials for Oracle DBA related things.

Undo is for rolling back transactions.
Redo is a performance optimisation of writes. It is important when restoring the system after a crash.

When you modify random million bytes on a disk, you don’t really have to wait for the disk to actually modify all the random blocks. The DB saves the change instructions in a linear redo and then executes the instructions one by one in the background. In the meantime, the blocks are served as they would have already been written.

@matste thanks you for detailed information. ☺️