view mercurial/txnutil.py @ 50317:af776c3d5c3e stable

debugdeltachain: stop summing the same chain over and over

Before this patch, delta chain size was computed from scratch for each chain,
disregarding the fact very likely already computed the same of length-1 prefix
for another revisions.

We not cache delta chain size and shortcut the computation when we see them.

Just for my mercurial-devel clone, this move the computation from about 17.5
second to about 4.8 seconds.

# txnutil.py - transaction related utilities
#
#  Copyright FUJIWARA Katsunori <[e-mail]> and others
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.


from . import encoding


def mayhavepending(root):
    """return whether 'root' may have pending changes, which are
    visible to this process.
    """
    return root == encoding.environ.get(b'HG_PENDING')


def trypending(root, vfs, filename, **kwargs):
    """Open  file to be read according to HG_PENDING environment variable

    This opens '.pending' of specified 'filename' only when HG_PENDING
    is equal to 'root'.

    This returns '(fp, is_pending_opened)' tuple.
    """
    if mayhavepending(root):
        try:
            return (vfs(b'%s.pending' % filename, **kwargs), True)
        except FileNotFoundError:
            pass
    return (vfs(filename, **kwargs), False)