nodemap: introduce append-only incremental update of the persistent data
Rewriting the full nodemap for each transaction has a cost we would like to
avoid. We introduce a new way to write persistent nodemap data by adding new
information at the end for file. Any new and updated block as added at the end
of the file. The last block is the new root node.
With this method, some of the block already on disk get "dereferenced" and
become dead data. In later changesets, We'll start tracking the amount of dead
data to eventually re-generate a full nodemap.
Differential Revision: https://phab.mercurial-scm.org/D7886
$ . "$TESTDIR/narrow-library.sh"
$ hg init master
$ cd master
$ echo treemanifest >> .hg/requires
$ echo 'contents of file' > file
$ mkdir foo
$ echo 'contents of foo/bar' > foo/bar
$ hg ci -Am 'some change'
adding file
adding foo/bar
$ cd ..
$ hg clone --narrow ssh://user@dummy/master copy --include=foo
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
new changesets * (glob)
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd copy
$ hg debugdirstate --no-dates
n * 20 * foo/bar (glob)
$ mv .hg/dirstate .hg/old_dirstate
$ dd bs=40 count=1 if=.hg/old_dirstate of=.hg/dirstate 2>/dev/null
$ hg debugdirstate
$ hg debugrebuilddirstate
$ hg debugdirstate
n * * unset foo/bar (glob)