Re: [Gnu-arch-users] Fast commits

[Robin Farine]

Aaron Bentley wrote:

> Unfortunately, commit is still an O(n) operation.  It's just a faster
> O(n) operation, because it uses the project tree to list all revisions
> instead of using the archive.


I wonder whether the following modification of the revision locking 
mechanism would work for O(1) commits.

An unlocked archive version directory contains a lock directory as follows:

foo--bar--1.0
         |
        + ---- base-0
         |
        ...
         |
        + ---- patch-N
         |
        + ---- ++version-lock
                            |
                           + ---- last-revision
                            |
                           + ---- +contents


where the file 'last-revision' in this example contains "patch-N".

During a commit, the client:

  1. checks that the working tree is up-to-date by reading
     ++version-lock/last-revision
  2. locks the version by renaming the ++version-lock directory
  3. reads and checks the last-revision file against the working tree
     again, computes the new revision name
  4. copies the new change set into the +contents directory, then moves
     it into its final revision directory
  5. updates the last-revision file, creates a new +contents directory
  6. renames the owned version lock directory back as ++version-lock,
     which  unlocks this version


I think that each step is almost what arch currently does (at least it 
should), the fact that the lock directory remains a direct child of the 
version directory excepted. This looks too easy, what did I miss?


Robin