branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
create verbosemmap.py
$ cat << EOF > verbosemmap.py
> # extension to make util.mmapread verbose
>
>
> from mercurial import (
> extensions,
> pycompat,
> util,
> )
>
> def extsetup(ui):
> def mmapread(orig, fp, *args):
> ui.write(b"mmapping %s\n" % pycompat.bytestr(fp.name))
> ui.flush()
> return orig(fp, *args)
>
> extensions.wrapfunction(util, 'mmapread', mmapread)
> EOF
setting up base repo
$ hg init a
$ cd a
$ touch a
$ hg add a
$ hg commit -qm base
$ for i in `$TESTDIR/seq.py 1 100` ; do
> echo $i > a
> hg commit -qm $i
> done
set up verbosemmap extension
$ cat << EOF >> $HGRCPATH
> [extensions]
> verbosemmap=$TESTTMP/verbosemmap.py
> EOF
mmap index which is now more than 4k long
$ hg log -l 5 -T '{rev}\n' --config experimental.mmapindexthreshold=4k
mmapping $TESTTMP/a/.hg/store/00changelog.i
mmapping $TESTTMP/a/.hg/store/00changelog-????????.nd (glob) (rust !)
100
99
98
97
96
do not mmap index which is still less than 32k
$ hg log -l 5 -T '{rev}\n' --config experimental.mmapindexthreshold=32k
mmapping $TESTTMP/a/.hg/store/00changelog-????????.nd (glob) (rust !)
100
99
98
97
96
$ cd ..