branchcache: use an explicit class for the v2 version
This prepare the introduction of an experimental v3 format version.
In the process, we move the description of the format in that new class.
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 ..