Adapted behaviour of ui.username() to documentation and mention it explicitly:
Searched in this order: $HGUSER, [ui] section of hgrcs, $EMAIL
and stop searching if one of these is set.
Abort if found username is an empty string to force specifying
the commit user elsewhere, e.g. with line option or repo hgrc.
If not found, use $LOGNAME or $USERNAME +"@full.hostname".
Mercurial git BK (*)
storage revlog delta compressed revisions SCCS weave
storage naming by filename by revision hash by filename
merge file DAGs changeset DAG file DAGs?
consistency SHA1 SHA1 CRC
signable? yes yes no
retrieve file tip O(1) O(1) O(revs)
add rev O(1) O(1) O(revs)
find prev file rev O(1) O(changesets) O(revs)
annotate file O(revs) O(changesets) O(revs)
find file changeset O(1) O(changesets) ?
checkout O(files) O(files) O(revs)?
commit O(changes) O(changes) ?
6 patches/s 6 patches/s slow
diff working dir O(changes) O(changes) ?
< 1s < 1s ?
tree diff revs O(changes) O(changes) ?
< 1s < 1s ?
hardlink clone O(files) O(revisions) O(files)
find remote csets O(log new) rsync: O(revisions) ?
git-http: O(changesets)
pull remote csets O(patch) O(modified files) O(patch)
repo growth O(patch) O(revisions) O(patch)
kernel history 300M 3.5G? 250M?
lines of code 2500 6500 (+ cogito) ??
* I've never used BK so this is just guesses