commit-graph: expire commit-graph files

As we merge commit-graph files in a commit-graph chain, we should clean
up the files that are no longer used.

This change introduces an 'expiry_window' value to the context, which is
always zero (for now). We then check the modified time of each
graph-{hash}.graph file in the $OBJDIR/info/commit-graphs folder and
unlink the files that are older than the expiry_window.

Since this is always zero, this immediately clears all unused graph
files. We will update the value to match a config setting in a future
change.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/technical/commit-graph.txt b/Documentation/technical/commit-graph.txt
index 473032e47696ec32bdff125afd16dc06fb563558..aed4350a5962286678ba6057b147706c2db5b982 100644 (file)
--- a/Documentation/technical/commit-graph.txt
+++ b/Documentation/technical/commit-graph.txt
@@ -266,6 +266,21 @@ The merge strategy values (2 for the size multiple, 64,000 for the maximum
 number of commits) could be extracted into config settings for full
 flexibility.
 
+## Deleting graph-{hash} files
+
+After a new tip file is written, some `graph-{hash}` files may no longer
+be part of a chain. It is important to remove these files from disk, eventually.
+The main reason to delay removal is that another process could read the
+`commit-graph-chain` file before it is rewritten, but then look for the
+`graph-{hash}` files after they are deleted.
+
+To allow holding old split commit-graphs for a while after they are unreferenced,
+we update the modified times of the files when they become unreferenced. Then,
+we scan the `$OBJDIR/info/commit-graphs/` directory for `graph-{hash}`
+files whose modified times are older than a given expiry window. This window
+defaults to zero, but can be changed using command-line arguments or a config
+setting.
+
 ## Chains across multiple object directories
 
 In a repo with alternates, we look for the `commit-graph-chain` file starting

diff --git a/commit-graph.c b/commit-graph.c
index fba705bc51e507368b75d671edd15c7eaf0fc5a7..0cc2ceb349a2dec9164e50143f73425618b94acc 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1652,6 +1652,70 @@ static void merge_commit_graphs(struct write_commit_graph_context *ctx)
        sort_and_scan_merged_commits(ctx);
 }
 
+static void mark_commit_graphs(struct write_commit_graph_context *ctx)
+{
+       uint32_t i;
+       time_t now = time(NULL);
+
+       for (i = ctx->num_commit_graphs_after - 1; i < ctx->num_commit_graphs_before; i++) {
+               struct stat st;
+               struct utimbuf updated_time;
+
+               stat(ctx->commit_graph_filenames_before[i], &st);
+
+               updated_time.actime = st.st_atime;
+               updated_time.modtime = now;
+               utime(ctx->commit_graph_filenames_before[i], &updated_time);
+       }
+}
+
+static void expire_commit_graphs(struct write_commit_graph_context *ctx)
+{
+       struct strbuf path = STRBUF_INIT;
+       DIR *dir;
+       struct dirent *de;
+       size_t dirnamelen;
+       time_t expire_time = time(NULL);
+
+       strbuf_addstr(&path, ctx->obj_dir);
+       strbuf_addstr(&path, "/info/commit-graphs");
+       dir = opendir(path.buf);
+
+       if (!dir) {
+               strbuf_release(&path);
+               return;
+       }
+
+       strbuf_addch(&path, '/');
+       dirnamelen = path.len;
+       while ((de = readdir(dir)) != NULL) {
+               struct stat st;
+               uint32_t i, found = 0;
+
+               strbuf_setlen(&path, dirnamelen);
+               strbuf_addstr(&path, de->d_name);
+
+               stat(path.buf, &st);
+
+               if (st.st_mtime > expire_time)
+                       continue;
+               if (path.len < 6 || strcmp(path.buf + path.len - 6, ".graph"))
+                       continue;
+
+               for (i = 0; i < ctx->num_commit_graphs_after; i++) {
+                       if (!strcmp(ctx->commit_graph_filenames_after[i],
+                                   path.buf)) {
+                               found = 1;
+                               break;
+                       }
+               }
+
+               if (!found)
+                       unlink(path.buf);
+
+       }
+}
+
 int write_commit_graph(const char *obj_dir,
                       struct string_list *pack_indexes,
                       struct string_list *commit_hex,
@@ -1764,6 +1828,11 @@ int write_commit_graph(const char *obj_dir,
 
        res = write_commit_graph_file(ctx);
 
+       if (ctx->split) {
+               mark_commit_graphs(ctx);
+               expire_commit_graphs(ctx);
+       }
+
 cleanup:
        free(ctx->graph_name);
        free(ctx->commits.list);

diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 46f0832f6801009624b644b3de1bb89696e7710c..76068ee4077e6c2a4cfaf6ed24832b5f0f1f335f 100755 (executable)
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -141,7 +141,7 @@ test_expect_success 'add one commit, write a merged graph' '
        test_path_is_file $graphdir/commit-graph-chain &&
        test_line_count = 2 $graphdir/commit-graph-chain &&
        ls $graphdir/graph-*.graph >graph-files &&
-       test_line_count = 4 graph-files &&
+       test_line_count = 2 graph-files &&
        verify_chain_files_exist $graphdir
 '