Registry Defragmenter [duplicate]

This question already has answers here: Rewrite Registry File in Windows (3 answers) Closed 9 years ago.

This is out of curiosity, but I have seen several (and some of them v开发者_如何学编程ery popular) software called registry defragmenter. While I can see the benefit they offer, but I am very curious on how exactly do you do registry defragmenting? Note that I'm not asking for software name, just a basic description of how it's done programmatically. I understand there is disk defragmenting API from microsoft. Is this that they are using? Or is there "registry defragmenting" api?

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While disk defragmenting would be helpful, the more important speed benefit which could be obtained would be arranging the registry nodes so that a typical depth-first search would put the sequentially-accessed nodes in the same registry page.

I'm not aware of any API for that. The algorithm is a straightforward reordering and rewriting operation, complicated by dealing with Windows' concurrent access.

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I suspect they're just defragmenting the files used to store registry information. Since the registry files are open during all normal Windows operation, a "normal" file defragmenting tool won't even touch them.

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Answer: Most parse the file format directly and manually.

There is another possible way: Using the RegSaveKey and then the RegReplaceKey functions, which are used by the Windows Backup utility.

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How do they prevent crashes in a live OS? Simple, they reroute API calls to the Windows Reg* functions and handle them themselves. Caching any changes that need to be written later. It would also be wise to hold an exclusive lock on the hive files.

I trust defragmenters MUCH more than I trust optimizers. Registry Optimizers can set untested or broken keys and enable broken features. With the mass commercialization of them, this is less of a problem. But still, with what I've seen in the past I don't trust them mucking my stable system up in ways that are too hard to pin down.