Where to place RemoveExistingProducts in a major MSI upgrade

When Windows Installer performs a major upgrade, the position of the RemoveExistingProducts action determines when the uninstall of the old product is performed. Despite efficiency, two factors dominate the decision

What should happen if either the install or the uninstall fails?
Should the new product ‘see’ registry entries/files/etc from the existing product or should the new product install ‘start from scratch’?

The following table summarizes the four possible approaches.

Position	Audit scripted?	Which product remains if …		Unchanged files are reinstalled?
Position	Audit scripted?	uninstall fails?	install fails?	Unchanged files are reinstalled?
Between InstallValidate and InstallInitializeRemove old, install new	No	Old	Neither	Yes
After InstallFinalizeInstall new, remove old	No	Both	Old	No
After InstallInitialize, before any script-generating actionsRemove old, install new	Yes	Old	Old	Yes
Between InstallExecute (or InstallExecuteAgain) and InstallFinalizeInstall new, remove old	Yes	Old	Old	No

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About me

Johannes Passing, M.Sc., living in Berlin, Germany.

Besides his consulting work, Johannes mainly focusses on Win32, COM, and NT kernel mode development, along with Java and .Net. He also is the author of cfix, a C/C++ unit testing framework for Win32 and NT kernel mode, Visual Assert, a Visual Studio Unit Testing-AddIn, and NTrace, a dynamic function boundary tracing toolkit for Windows NT/x86 kernel/user mode code.

Contact Johannes: jpassing (at) acm org

Johannes' GPG fingerprint is BBB1 1769 B82D CD07 D90A 57E8 9FE1 D441 F7A0 1BB1.