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builtin/commit-graph.c: support for '--split[=<strategy>]'

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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>
This commit is contained in:
Taylor Blau
2020-04-13 22:04:08 -06:00
committed by Junio C Hamano
parent 2fa05f31bd
commit 4f027355f6
3 changed files with 33 additions and 9 deletions
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26
builtin/commit-graph.c
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@ -9,7 +9,9 @@
static char const * const builtin_commit_graph_usage[] = {
N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--[no-]progress] <split options>"),
N_("git commit-graph write [--object-dir <objdir>] [--append] "
"[--split[=<strategy>]] [--reachable|--stdin-packs|--stdin-commits] "
"[--[no-]progress] <split options>"),
NULL
};
@ -19,7 +21,9 @@ static const char * const builtin_commit_graph_verify_usage[] = {
};
static const char * const builtin_commit_graph_write_usage[] = {
N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--[no-]progress] <split options>"),
N_("git commit-graph write [--object-dir <objdir>] [--append] "
"[--split[=<strategy>]] [--reachable|--stdin-packs|--stdin-commits] "
"[--[no-]progress] <split options>"),
NULL
};
@ -111,6 +115,18 @@ static int graph_verify(int argc, const char **argv)
extern int read_replace_refs;
static struct split_commit_graph_opts split_opts;
static int write_option_parse_split(const struct option *opt, const char *arg,
int unset)
{
opts.split = 1;
if (!arg)
return 0;
die(_("unrecognized --split argument, %s"), arg);
return 0;
}
static int graph_write(int argc, const char **argv)
{
struct string_list *pack_indexes = NULL;
@ -133,8 +149,10 @@ static int graph_write(int argc, const char **argv)
OPT_BOOL(0, "append", &opts.append,
N_("include all commits already in the commit-graph file")),
OPT_BOOL(0, "progress", &opts.progress, N_("force progress reporting")),
OPT_BOOL(0, "split", &opts.split,
N_("allow writing an incremental commit-graph file")),
OPT_CALLBACK_F(0, "split", &split_opts.flags, NULL,
N_("allow writing an incremental commit-graph file"),
PARSE_OPT_OPTARG | PARSE_OPT_NONEG,
write_option_parse_split),
OPT_INTEGER(0, "max-commits", &split_opts.max_commits,
N_("maximum number of commits in a non-base split commit-graph")),
OPT_INTEGER(0, "size-multiple", &split_opts.size_multiple,