builtin/commit-graph.c: support for '--split[=<strategy>]'
With '--split', the commit-graph machinery writes new commits in another
incremental commit-graph which is part of the existing chain, and
optionally decides to condense the chain into a single commit-graph.
This is done to ensure that the asymptotic behavior of looking up a
commit in an incremental chain is not dominated by the number of
incrementals in that chain. It can be controlled by the '--max-commits'
and '--size-multiple' options.
In the next two commits, we will introduce additional splitting
strategies that can exert additional control over:
- when a split commit-graph is and isn't written, and
- when the existing commit-graph chain is discarded completely and
replaced with another graph
To prepare for this, make '--split' take an optional strategy (as in
'--split[=<strategy>]'), and add a new enum to describe which strategy
is being used. For now, no strategies are given, and the only enumerated
value is 'COMMIT_GRAPH_SPLIT_UNSPECIFIED', indicating the absence of a
strategy.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 28d1fee..10d757c 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -57,11 +57,12 @@
With the `--append` option, include all commits that are present in the
existing commit-graph file.
+
-With the `--split` option, write the commit-graph as a chain of multiple
-commit-graph files stored in `<dir>/info/commit-graphs`. The new commits
-not already in the commit-graph are added in a new "tip" file. This file
-is merged with the existing file if the following merge conditions are
-met:
+With the `--split[=<strategy>]` option, write the commit-graph as a
+chain of multiple commit-graph files stored in
+`<dir>/info/commit-graphs`. Commit-graph layers are merged based on the
+strategy and other splitting options. The new commits not already in the
+commit-graph are added in a new "tip" file. This file is merged with the
+existing file if the following merge conditions are met:
+
* If `--size-multiple=<X>` is not specified, let `X` equal 2. If the new
tip file would have `N` commits and the previous tip has `M` commits and
