jeffpc added a comment.
In https://phab.mercurial-scm.org/D2945#58586, @pulkit wrote: > There is a suggestion from @jeffpc to have a plain text header in statefiles like `HGStateFile` so that user can grep for them or look into files and know that they are state files. How does that sound? > (@jeffpc I am not sure I explained this correctly, it will be great if you can chime in.) I don't really care about the actual string value, I just think it is a good storage design practice to have every on-disk structure contain a magic value of some sort. (Beware, I have a storage background and therefore opinions about these things... ;) ) This makes it easier to do all sort of data recovery should the need arise. E.g., - if you know that a random file (e.g., from lost+found) is a hg state file, you can ignore/delete it and just reclone your repos - hg can detect some corruption better, and depending on the state file regenerate it or error out - hg developers can more easily sort out what's what when looking at buffers/files/etc. - as an added bonus, the magic can be used for format versioning FWIW, the three major things that I consider essential to good on-disk structures: 1. magic numbers - see above 2. checksums - possibly two checksums: one for the header and one for the payload 3. back-pointers - see below Back-pointers allow you to tie the file/buffer into the bigger context - be it which state file it is, or which repository it belongs to. In this case a state file's back-pointer could be something like the repo-id + state-file-name stored in the state file's header. (I realize that there is no repo-id, but in general some approximation of it tends to be better than nothing.) This should make it painfully obvious what data one is dealing with and how to parse/interpret it just by looking at the byte-stream without any other context. REPOSITORY rHG Mercurial REVISION DETAIL https://phab.mercurial-scm.org/D2945 To: pulkit, #hg-reviewers Cc: jeffpc, yuja, mercurial-devel _______________________________________________ Mercurial-devel mailing list Mercurial-devel@mercurial-scm.org https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel
