What is the use of Repair option in a msi installer and what does it really do (internally)?

Question

I have a software package deployed using WIX. When I run the installer again after installing, it gives as option to repair, what does it exactly do?

Answer 1

The links by @Stein Asmul explains the quite a lot of things in depth, to me in simple words this is what MSI repair/self healing does. If you have written the MSI you know that it consists of multiple features and each feature is made up of multiple components. Th repair option in simple words compares the ID/Primary Key for each component with that of the workstation in which it is running. If one of the component ID/Primary key is missing on the workstation it will re-install that component.

For example, if we have 2 components Component one to install abc.txt and Component two to install xyz.txt. The repair will go and check the ID/Primary key of Component 1 and Component 2 to make sure they exist of the workstation/server. If it's not present it will reinstall it. @Stein Asmul's links should have more details, this is a very simple short answer to it.