Undo/Redo Mechanism
The undo/redo level specified in the Settings (Editor) defines the number of operations that you can undo or redo at any moment and in a given context. The greater the number, the more information saved in memory by Patchwork 3D. It is possible to have an unlimited number of memorized operations. However, each memorized operation may occupy a large amount of memory. A limit of 20 operations is generally sufficient.
The undo/redo operations are not saved in the P3D database: when you load a database, you cannot undo any of the operations performed during a previous editing session.
Edit >
Undo All or Edit > 
Redo All: Undo all memorized operations at once.File > Discard P3D Operation History: Discard the memory of all information used to undo previous operations in the application. This operation can free up a large amount of memory and significantly reduce the side of the file during the next save.
Edit > Discard Module Undo History: Discard only the undo operations in the current module (Shaper or Matter).