[PATCH 2 of 8] transaction: track newly introduced revisions

[Jun Wu]

Excerpts from Pierre-Yves David's message of 2017-05-03 01:43:39 +0200:
> # HG changeset patch
> # User Pierre-Yves David <pierre-yves.david at ens-lyon.org>
> # Date 1493743551 -7200
> #      Tue May 02 18:45:51 2017 +0200
> # Branch stable
> # Node ID 76a035851a620dcf36a6dd18a37409dff43c6d42
> # Parent  6697da7c4eab3fbe3588a2f91fa3f99b16f808ac
> # EXP-Topic obscache
> # Available At https://www.mercurial-scm.org/repo/users/marmoute/mercurial/ 
> #              hg pull https://www.mercurial-scm.org/repo/users/marmoute/mercurial/  -r 76a035851a62
> transaction: track newly introduced revisions
> 
> Tracking revisions is not the data that will unlock the most new capability.
> However, they are the simplest thing to track and still unlock some nice
> improvements in regard with caching.
> 
> We plug ourself at the changelog level to make sure we do not miss any revision
> additions.
> 
> The 'revs' set is configured at the repository level because the transaction
> itself does not needs to know that much about the business logic.
> 
> diff --git a/mercurial/changelog.py b/mercurial/changelog.py
> --- a/mercurial/changelog.py
> +++ b/mercurial/changelog.py
> @@ -535,3 +535,14 @@ class changelog(revlog.revlog):
>          just to access this is costly."""
>          extra = self.read(rev)[5]
>          return encoding.tolocal(extra.get("branch")), 'close' in extra
> +
> +    def _addrevision(self, node, rawtext, transaction, *args, **kwargs):
> +        # overlay over the standard revlog._addrevision to track the new
> +        # revision on the transaction.
> +        rev = len(self)
> +        node = super(changelog, self)._addrevision(node, rawtext, transaction,
> +                                                   *args, **kwargs)
> +        revs = transaction.changes.get('revs')
> +        if revs is not None:
> +            revs.add(rev)

Since changelog is append-only, and strip won't happen during a transaction.
Why not just record len(changelog) during transaction start, and test
len(changelog) at the end of transaction? That's O(1), instead of O(N log N)
here.

> +        return node
> diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
> --- a/mercurial/localrepo.py
> +++ b/mercurial/localrepo.py
> @@ -1100,6 +1100,7 @@ class localrepository(object):
>                                       self.store.createmode,
>                                       validator=validate,
>                                       releasefn=releasefn)
> +        tr.changes['revs'] = set()
>  
>          tr.hookargs['txnid'] = txnid
>          # note: writing the fncache only during finalize mean that the file is