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
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
revision 0
branch default
phase draft
adda
$ echo b > b
$ hg ci -Am addb
adding b
$ hg log -T '{node}\n'
102a90ea7b4a3361e4082ed620918c261189a36a
07f4944404050f47db2e5c5071e0e84e7a27bba9
$ hg debug-diff-tree 07f494440405 102a90ea7b4a
:000000 100664 000000000000 1e88685f5dde N b b
$ hg debug-diff-tree 07f494440405 102a90ea7b4a --patch
diff --git a/b b/b
new file mode 100644
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+b
Ensure that diff-tree output isn't affected by diffopts
$ hg --config diff.noprefix=True debug-diff-tree 07f494440405 102a90ea7b4a
:000000 100664 000000000000 1e88685f5dde N b b
$ hg --config diff.noprefix=True debug-diff-tree --patch 07f494440405 102a90ea7b4a
diff --git a/b b/b
new file mode 100644
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+b
$ cd ..