How to transfer learned conversions to new computer on Windows

[niwazukihon]

Hi, I'm wondering how to transfer the "typing habits" mozc learned over time on a Windows system to another Windows system. I know I can already export/import the user dictionaries, but I want, for example, the custom words I created by manually typing them out, without adding them explicitly to a dictionary.

It seems on Windows the data is at C:\Users\<User-name>\AppData\LocalLow\Mozc, and the files history.db, segment.db, boundary.db, and cform.db contain the info I'm after, while user_dictionary.db contains user dictionaries, which I also want to transfer.

However, it seems that history.db is hidden and encrypted. I'm also not sure about if I can just copy and paste the other data files. I would appreciate if I can get a guide on exactly how to transfer everything to a new computer on Windows. Thank you.

[qoxmfaktmxj]

Short answer: everything except history.db can be copied. history.db is tied to the old machine by design.

Why history.db can't be moved

In the Mozc source, the user history (user://history.db) is read through EncryptedStringStorage. The encryption key is a random password stored in encrypt_key.db in the same folder, and on Windows that password is itself protected with CryptProtectData (DPAPI) for the current Windows user (see base/password_manager.cc and base/encryptor.cc). DPAPI data can only be decrypted by the same user on the same machine, so even if you copy both history.db and encrypt_key.db, the new PC can't decrypt them. Mozc then logs "Can't load user history data." and starts with an empty history. There's no export for this data.

What you can transfer

• user_dictionary.db: use Dictionary Tool > export/import as you already know, or copy the file.
• segment.db, boundary.db, cform.db: these are plain LRU storage files (not encrypted), holding learned segment choices and boundaries. You can copy them over.

Steps:

1. On the old PC, copy %USERPROFILE%\AppData\LocalLow\Mozc\ segment.db, boundary.db, cform.db (and user_dictionary.db if you don't use export).
2. On the new PC, make sure Mozc isn't running (sign out and back in, or copy before you first use it), then put the files in the same folder, replacing the ones there. Mozc keeps its data in memory and writes it back, so copying while it's running may get overwritten.
3. Don't copy history.db / encrypt_key.db. Let the new PC create its own.

For the words you only ever typed by hand and care about keeping, the reliable way is to add them to the user dictionary once, since that part is portable.