Is Registry Compactor Safe?

tullik

Is Registry Compactor Safe?

Plamen234 wrote
... ps2: I intend to defrag the reg (never done this before) with registry compactor but I am a little afraid about such intervention (a reg save is compulsory I guess)

It is pretty safe. The compaction is done with two Windows APIs, described briefly in this 1999 article (Inside the Registry) on Microsoft TechNet under the heading Registry Optimizations.

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Here are some forum highpoints in the history:

Why include the feature in Power Tools?

... the risk exposure ...

... getting closer ...

... the breakthrough ...

Compact without restart! Dangerous???

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To Restart or not to Restart?

When a hive is compacted and Windows has switched to the new hive, the old hive still exists. In jv16pt, the old hive file has a suffix of "bak_jv16pt." The old hive can still have open handles -- this may be a Windows bug. In any case, a Restart clears the handles.

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To be extra safe, one could create a system restore point before doing the compaction. I haven't done this since the Technet article convinced me the process is safe enough. It is your call.

tullik

Here's some additional information about the PT 2006 Registry Compactor.

As you have probably seen, the Registry Compactor window displays four columns (screenshots below), normally for 11 hives. Where does PT get the information shown?

Hive -- from the registry key HKLM\Sys\CurrentControlSet\Control\hivelist (99.9% certain), probably via API calls..

Storage file -- the active hive file paths (except for the drive prefix, e.g., C:\) are values under that key. Those values have a string prefix like Device\HarddiskVolume1. I don't know if the string is converted to a drive letter by an API, or if PT converts some other registry value (perhaps from a binary value in HKLM\Sys\Setup, Name=SystemPrefix).

Note: the conversion (however it is done) has in rare cases failed, most often when the registry is on a drive other than C.

Size before -- this is probably obtained by PT using an API to obtain the filename properties.

Size after -- same method as Size before for hives successfully compacted. Otherwise, and initially, shows as N/A.

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Capability observation:

If you have (or create) another admin account with a password, you can start PT from a shortcut using "right click...Run as..."

Registry Compactor and HKLM\Sys\CurrentControlSet\Control\hivelist then show 2 additional hives (for the "Run as..." userID).

Registry Compactor can compact those 2 hives as well as the 11 normally associated with your userID.

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Registry Compactor thumbnail, sorted by "Size before", showing all columns:

Comparison of hive file sizes shown by Registry Compactor and File finder:

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~~Regedit thumbnail showing values under HKLM\Sys\CurrentControlSet\Control\hivelist :~~