Merge branch 'ds/commit-graph-incremental'
[gitweb.git] / commit-graph.c
index 8cc1d1d6c3aff0842c42ecda5cc545c9eb085802..fe954ab5f845e65bc5cad987308aeb6598f2fd24 100644 (file)
@@ -22,6 +22,7 @@
 #define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
 #define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
 #define GRAPH_CHUNKID_EXTRAEDGES 0x45444745 /* "EDGE" */
+#define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */
 
 #define GRAPH_DATA_WIDTH (the_hash_algo->rawsz + 16)
 
 
 char *get_commit_graph_filename(const char *obj_dir)
 {
-       return xstrfmt("%s/info/commit-graph", obj_dir);
+       char *filename = xstrfmt("%s/info/commit-graph", obj_dir);
+       char *normalized = xmalloc(strlen(filename) + 1);
+       normalize_path_copy(normalized, filename);
+       free(filename);
+       return normalized;
+}
+
+static char *get_split_graph_filename(const char *obj_dir,
+                                     const char *oid_hex)
+{
+       char *filename = xstrfmt("%s/info/commit-graphs/graph-%s.graph",
+                                obj_dir,
+                                oid_hex);
+       char *normalized = xmalloc(strlen(filename) + 1);
+       normalize_path_copy(normalized, filename);
+       free(filename);
+       return normalized;
+}
+
+static char *get_chain_filename(const char *obj_dir)
+{
+       return xstrfmt("%s/info/commit-graphs/commit-graph-chain", obj_dir);
 }
 
 static uint8_t oid_version(void)
@@ -249,6 +271,12 @@ struct commit_graph *parse_commit_graph(void *graph_map, int fd,
                        else
                                graph->chunk_extra_edges = data + chunk_offset;
                        break;
+
+               case GRAPH_CHUNKID_BASE:
+                       if (graph->chunk_base_graphs)
+                               chunk_repeated = 1;
+                       else
+                               graph->chunk_base_graphs = data + chunk_offset;
                }
 
                if (chunk_repeated) {
@@ -267,6 +295,8 @@ struct commit_graph *parse_commit_graph(void *graph_map, int fd,
                last_chunk_offset = chunk_offset;
        }
 
+       hashcpy(graph->oid.hash, graph->data + graph->data_len - graph->hash_len);
+
        if (verify_commit_graph_lite(graph)) {
                free(graph);
                return NULL;
@@ -280,26 +310,152 @@ static struct commit_graph *load_commit_graph_one(const char *graph_file)
 
        struct stat st;
        int fd;
+       struct commit_graph *g;
        int open_ok = open_commit_graph(graph_file, &fd, &st);
 
        if (!open_ok)
                return NULL;
 
-       return load_commit_graph_one_fd_st(fd, &st);
+       g = load_commit_graph_one_fd_st(fd, &st);
+
+       if (g)
+               g->filename = xstrdup(graph_file);
+
+       return g;
+}
+
+static struct commit_graph *load_commit_graph_v1(struct repository *r, const char *obj_dir)
+{
+       char *graph_name = get_commit_graph_filename(obj_dir);
+       struct commit_graph *g = load_commit_graph_one(graph_name);
+       free(graph_name);
+
+       if (g)
+               g->obj_dir = obj_dir;
+
+       return g;
+}
+
+static int add_graph_to_chain(struct commit_graph *g,
+                             struct commit_graph *chain,
+                             struct object_id *oids,
+                             int n)
+{
+       struct commit_graph *cur_g = chain;
+
+       if (n && !g->chunk_base_graphs) {
+               warning(_("commit-graph has no base graphs chunk"));
+               return 0;
+       }
+
+       while (n) {
+               n--;
+
+               if (!cur_g ||
+                   !oideq(&oids[n], &cur_g->oid) ||
+                   !hasheq(oids[n].hash, g->chunk_base_graphs + g->hash_len * n)) {
+                       warning(_("commit-graph chain does not match"));
+                       return 0;
+               }
+
+               cur_g = cur_g->base_graph;
+       }
+
+       g->base_graph = chain;
+
+       if (chain)
+               g->num_commits_in_base = chain->num_commits + chain->num_commits_in_base;
+
+       return 1;
+}
+
+static struct commit_graph *load_commit_graph_chain(struct repository *r, const char *obj_dir)
+{
+       struct commit_graph *graph_chain = NULL;
+       struct strbuf line = STRBUF_INIT;
+       struct stat st;
+       struct object_id *oids;
+       int i = 0, valid = 1, count;
+       char *chain_name = get_chain_filename(obj_dir);
+       FILE *fp;
+       int stat_res;
+
+       fp = fopen(chain_name, "r");
+       stat_res = stat(chain_name, &st);
+       free(chain_name);
+
+       if (!fp ||
+           stat_res ||
+           st.st_size <= the_hash_algo->hexsz)
+               return NULL;
+
+       count = st.st_size / (the_hash_algo->hexsz + 1);
+       oids = xcalloc(count, sizeof(struct object_id));
+
+       prepare_alt_odb(r);
+
+       for (i = 0; i < count; i++) {
+               struct object_directory *odb;
+
+               if (strbuf_getline_lf(&line, fp) == EOF)
+                       break;
+
+               if (get_oid_hex(line.buf, &oids[i])) {
+                       warning(_("invalid commit-graph chain: line '%s' not a hash"),
+                               line.buf);
+                       valid = 0;
+                       break;
+               }
+
+               valid = 0;
+               for (odb = r->objects->odb; odb; odb = odb->next) {
+                       char *graph_name = get_split_graph_filename(odb->path, line.buf);
+                       struct commit_graph *g = load_commit_graph_one(graph_name);
+
+                       free(graph_name);
+
+                       if (g) {
+                               g->obj_dir = odb->path;
+
+                               if (add_graph_to_chain(g, graph_chain, oids, i)) {
+                                       graph_chain = g;
+                                       valid = 1;
+                               }
+
+                               break;
+                       }
+               }
+
+               if (!valid) {
+                       warning(_("unable to find all commit-graph files"));
+                       break;
+               }
+       }
+
+       free(oids);
+       fclose(fp);
+       strbuf_release(&line);
+
+       return graph_chain;
+}
+
+struct commit_graph *read_commit_graph_one(struct repository *r, const char *obj_dir)
+{
+       struct commit_graph *g = load_commit_graph_v1(r, obj_dir);
+
+       if (!g)
+               g = load_commit_graph_chain(r, obj_dir);
+
+       return g;
 }
 
 static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
 {
-       char *graph_name;
 
        if (r->objects->commit_graph)
                return;
 
-       graph_name = get_commit_graph_filename(obj_dir);
-       r->objects->commit_graph =
-               load_commit_graph_one(graph_name);
-
-       FREE_AND_NULL(graph_name);
+       r->objects->commit_graph = read_commit_graph_one(r, obj_dir);
 }
 
 /*
@@ -361,9 +517,18 @@ int generation_numbers_enabled(struct repository *r)
        return !!first_generation;
 }
 
+static void close_commit_graph_one(struct commit_graph *g)
+{
+       if (!g)
+               return;
+
+       close_commit_graph_one(g->base_graph);
+       free_commit_graph(g);
+}
+
 void close_commit_graph(struct raw_object_store *o)
 {
-       free_commit_graph(o->commit_graph);
+       close_commit_graph_one(o->commit_graph);
        o->commit_graph = NULL;
 }
 
@@ -373,18 +538,38 @@ static int bsearch_graph(struct commit_graph *g, struct object_id *oid, uint32_t
                            g->chunk_oid_lookup, g->hash_len, pos);
 }
 
+static void load_oid_from_graph(struct commit_graph *g,
+                               uint32_t pos,
+                               struct object_id *oid)
+{
+       uint32_t lex_index;
+
+       while (g && pos < g->num_commits_in_base)
+               g = g->base_graph;
+
+       if (!g)
+               BUG("NULL commit-graph");
+
+       if (pos >= g->num_commits + g->num_commits_in_base)
+               die(_("invalid commit position. commit-graph is likely corrupt"));
+
+       lex_index = pos - g->num_commits_in_base;
+
+       hashcpy(oid->hash, g->chunk_oid_lookup + g->hash_len * lex_index);
+}
+
 static struct commit_list **insert_parent_or_die(struct repository *r,
                                                 struct commit_graph *g,
-                                                uint64_t pos,
+                                                uint32_t pos,
                                                 struct commit_list **pptr)
 {
        struct commit *c;
        struct object_id oid;
 
-       if (pos >= g->num_commits)
-               die("invalid parent position %"PRIu64, pos);
+       if (pos >= g->num_commits + g->num_commits_in_base)
+               die("invalid parent position %"PRIu32, pos);
 
-       hashcpy(oid.hash, g->chunk_oid_lookup + g->hash_len * pos);
+       load_oid_from_graph(g, pos, &oid);
        c = lookup_commit(r, &oid);
        if (!c)
                die(_("could not find commit %s"), oid_to_hex(&oid));
@@ -394,7 +579,14 @@ static struct commit_list **insert_parent_or_die(struct repository *r,
 
 static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, uint32_t pos)
 {
-       const unsigned char *commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * pos;
+       const unsigned char *commit_data;
+       uint32_t lex_index;
+
+       while (pos < g->num_commits_in_base)
+               g = g->base_graph;
+
+       lex_index = pos - g->num_commits_in_base;
+       commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * lex_index;
        item->graph_pos = pos;
        item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
 }
@@ -412,10 +604,25 @@ static int fill_commit_in_graph(struct repository *r,
        uint32_t *parent_data_ptr;
        uint64_t date_low, date_high;
        struct commit_list **pptr;
-       const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
+       const unsigned char *commit_data;
+       uint32_t lex_index;
 
-       item->object.parsed = 1;
+       while (pos < g->num_commits_in_base)
+               g = g->base_graph;
+
+       if (pos >= g->num_commits + g->num_commits_in_base)
+               die(_("invalid commit position. commit-graph is likely corrupt"));
+
+       /*
+        * Store the "full" position, but then use the
+        * "local" position for the rest of the calculation.
+        */
        item->graph_pos = pos;
+       lex_index = pos - g->num_commits_in_base;
+
+       commit_data = g->chunk_commit_data + (g->hash_len + 16) * lex_index;
+
+       item->object.parsed = 1;
 
        set_commit_tree(item, NULL);
 
@@ -459,7 +666,18 @@ static int find_commit_in_graph(struct commit *item, struct commit_graph *g, uin
                *pos = item->graph_pos;
                return 1;
        } else {
-               return bsearch_graph(g, &(item->object.oid), pos);
+               struct commit_graph *cur_g = g;
+               uint32_t lex_index;
+
+               while (cur_g && !bsearch_graph(cur_g, &(item->object.oid), &lex_index))
+                       cur_g = cur_g->base_graph;
+
+               if (cur_g) {
+                       *pos = lex_index + cur_g->num_commits_in_base;
+                       return 1;
+               }
+
+               return 0;
        }
 }
 
@@ -499,8 +717,13 @@ static struct tree *load_tree_for_commit(struct repository *r,
                                         struct commit *c)
 {
        struct object_id oid;
-       const unsigned char *commit_data = g->chunk_commit_data +
-                                          GRAPH_DATA_WIDTH * (c->graph_pos);
+       const unsigned char *commit_data;
+
+       while (c->graph_pos < g->num_commits_in_base)
+               g = g->base_graph;
+
+       commit_data = g->chunk_commit_data +
+                       GRAPH_DATA_WIDTH * (c->graph_pos - g->num_commits_in_base);
 
        hashcpy(oid.hash, commit_data);
        set_commit_tree(c, lookup_tree(r, &oid));
@@ -539,7 +762,7 @@ struct packed_oid_list {
 
 struct write_commit_graph_context {
        struct repository *r;
-       const char *obj_dir;
+       char *obj_dir;
        char *graph_name;
        struct packed_oid_list oids;
        struct packed_commit_list commits;
@@ -548,8 +771,21 @@ struct write_commit_graph_context {
        struct progress *progress;
        int progress_done;
        uint64_t progress_cnt;
+
+       char *base_graph_name;
+       int num_commit_graphs_before;
+       int num_commit_graphs_after;
+       char **commit_graph_filenames_before;
+       char **commit_graph_filenames_after;
+       char **commit_graph_hash_after;
+       uint32_t new_num_commits_in_base;
+       struct commit_graph *new_base_graph;
+
        unsigned append:1,
-                report_progress:1;
+                report_progress:1,
+                split:1;
+
+       const struct split_commit_graph_opts *split_opts;
 };
 
 static void write_graph_chunk_fanout(struct hashfile *f,
@@ -619,6 +855,16 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
                                              ctx->commits.nr,
                                              commit_to_sha1);
 
+                       if (edge_value >= 0)
+                               edge_value += ctx->new_num_commits_in_base;
+                       else {
+                               uint32_t pos;
+                               if (find_commit_in_graph(parent->item,
+                                                        ctx->new_base_graph,
+                                                        &pos))
+                                       edge_value = pos;
+                       }
+
                        if (edge_value < 0)
                                BUG("missing parent %s for commit %s",
                                    oid_to_hex(&parent->item->object.oid),
@@ -639,6 +885,17 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
                                              ctx->commits.list,
                                              ctx->commits.nr,
                                              commit_to_sha1);
+
+                       if (edge_value >= 0)
+                               edge_value += ctx->new_num_commits_in_base;
+                       else {
+                               uint32_t pos;
+                               if (find_commit_in_graph(parent->item,
+                                                        ctx->new_base_graph,
+                                                        &pos))
+                                       edge_value = pos;
+                       }
+
                        if (edge_value < 0)
                                BUG("missing parent %s for commit %s",
                                    oid_to_hex(&parent->item->object.oid),
@@ -696,6 +953,16 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
                                                  ctx->commits.nr,
                                                  commit_to_sha1);
 
+                       if (edge_value >= 0)
+                               edge_value += ctx->new_num_commits_in_base;
+                       else {
+                               uint32_t pos;
+                               if (find_commit_in_graph(parent->item,
+                                                        ctx->new_base_graph,
+                                                        &pos))
+                                       edge_value = pos;
+                       }
+
                        if (edge_value < 0)
                                BUG("missing parent %s for commit %s",
                                    oid_to_hex(&parent->item->object.oid),
@@ -710,7 +977,7 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
        }
 }
 
-static int commit_compare(const void *_a, const void *_b)
+static int oid_compare(const void *_a, const void *_b)
 {
        const struct object_id *a = (const struct object_id *)_a;
        const struct object_id *b = (const struct object_id *)_b;
@@ -787,7 +1054,13 @@ static void close_reachable(struct write_commit_graph_context *ctx)
                display_progress(ctx->progress, i + 1);
                commit = lookup_commit(ctx->r, &ctx->oids.list[i]);
 
-               if (commit && !parse_commit_no_graph(commit))
+               if (!commit)
+                       continue;
+               if (ctx->split) {
+                       if (!parse_commit(commit) &&
+                           commit->graph_pos == COMMIT_NOT_FROM_GRAPH)
+                               add_missing_parents(ctx, commit);
+               } else if (!parse_commit_no_graph(commit))
                        add_missing_parents(ctx, commit);
        }
        stop_progress(&ctx->progress);
@@ -861,14 +1134,15 @@ static int add_ref_to_list(const char *refname,
        return 0;
 }
 
-int write_commit_graph_reachable(const char *obj_dir, unsigned int flags)
+int write_commit_graph_reachable(const char *obj_dir, unsigned int flags,
+                                const struct split_commit_graph_opts *split_opts)
 {
        struct string_list list = STRING_LIST_INIT_DUP;
        int result;
 
        for_each_ref(add_ref_to_list, &list);
        result = write_commit_graph(obj_dir, NULL, &list,
-                                   flags);
+                                   flags, split_opts);
 
        string_list_clear(&list, 0);
        return result;
@@ -913,7 +1187,7 @@ static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
        }
 
        stop_progress(&ctx->progress);
-       strbuf_reset(&progress_title);
+       strbuf_release(&progress_title);
        strbuf_release(&packname);
 
        return 0;
@@ -979,12 +1253,20 @@ static uint32_t count_distinct_commits(struct write_commit_graph_context *ctx)
                        _("Counting distinct commits in commit graph"),
                        ctx->oids.nr);
        display_progress(ctx->progress, 0); /* TODO: Measure QSORT() progress */
-       QSORT(ctx->oids.list, ctx->oids.nr, commit_compare);
+       QSORT(ctx->oids.list, ctx->oids.nr, oid_compare);
 
        for (i = 1; i < ctx->oids.nr; i++) {
                display_progress(ctx->progress, i + 1);
-               if (!oideq(&ctx->oids.list[i - 1], &ctx->oids.list[i]))
+               if (!oideq(&ctx->oids.list[i - 1], &ctx->oids.list[i])) {
+                       if (ctx->split) {
+                               struct commit *c = lookup_commit(ctx->r, &ctx->oids.list[i]);
+
+                               if (!c || c->graph_pos != COMMIT_NOT_FROM_GRAPH)
+                                       continue;
+                       }
+
                        count_distinct++;
+               }
        }
        stop_progress(&ctx->progress);
 
@@ -1007,7 +1289,13 @@ static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
                if (i > 0 && oideq(&ctx->oids.list[i - 1], &ctx->oids.list[i]))
                        continue;
 
+               ALLOC_GROW(ctx->commits.list, ctx->commits.nr + 1, ctx->commits.alloc);
                ctx->commits.list[ctx->commits.nr] = lookup_commit(ctx->r, &ctx->oids.list[i]);
+
+               if (ctx->split &&
+                   ctx->commits.list[ctx->commits.nr]->graph_pos != COMMIT_NOT_FROM_GRAPH)
+                       continue;
+
                parse_commit_no_graph(ctx->commits.list[ctx->commits.nr]);
 
                for (parent = ctx->commits.list[ctx->commits.nr]->parents;
@@ -1022,18 +1310,56 @@ static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
        stop_progress(&ctx->progress);
 }
 
+static int write_graph_chunk_base_1(struct hashfile *f,
+                                   struct commit_graph *g)
+{
+       int num = 0;
+
+       if (!g)
+               return 0;
+
+       num = write_graph_chunk_base_1(f, g->base_graph);
+       hashwrite(f, g->oid.hash, the_hash_algo->rawsz);
+       return num + 1;
+}
+
+static int write_graph_chunk_base(struct hashfile *f,
+                                 struct write_commit_graph_context *ctx)
+{
+       int num = write_graph_chunk_base_1(f, ctx->new_base_graph);
+
+       if (num != ctx->num_commit_graphs_after - 1) {
+               error(_("failed to write correct number of base graph ids"));
+               return -1;
+       }
+
+       return 0;
+}
+
 static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 {
        uint32_t i;
+       int fd;
        struct hashfile *f;
        struct lock_file lk = LOCK_INIT;
-       uint32_t chunk_ids[5];
-       uint64_t chunk_offsets[5];
+       uint32_t chunk_ids[6];
+       uint64_t chunk_offsets[6];
        const unsigned hashsz = the_hash_algo->rawsz;
        struct strbuf progress_title = STRBUF_INIT;
-       int num_chunks = ctx->num_extra_edges ? 4 : 3;
+       int num_chunks = 3;
+       struct object_id file_hash;
+
+       if (ctx->split) {
+               struct strbuf tmp_file = STRBUF_INIT;
+
+               strbuf_addf(&tmp_file,
+                           "%s/info/commit-graphs/tmp_graph_XXXXXX",
+                           ctx->obj_dir);
+               ctx->graph_name = strbuf_detach(&tmp_file, NULL);
+       } else {
+               ctx->graph_name = get_commit_graph_filename(ctx->obj_dir);
+       }
 
-       ctx->graph_name = get_commit_graph_filename(ctx->obj_dir);
        if (safe_create_leading_directories(ctx->graph_name)) {
                UNLEAK(ctx->graph_name);
                error(_("unable to create leading directories of %s"),
@@ -1041,30 +1367,61 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
                return -1;
        }
 
-       hold_lock_file_for_update(&lk, ctx->graph_name, LOCK_DIE_ON_ERROR);
-       f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
+       if (ctx->split) {
+               char *lock_name = get_chain_filename(ctx->obj_dir);
 
-       hashwrite_be32(f, GRAPH_SIGNATURE);
+               hold_lock_file_for_update(&lk, lock_name, LOCK_DIE_ON_ERROR);
 
-       hashwrite_u8(f, GRAPH_VERSION);
-       hashwrite_u8(f, oid_version());
-       hashwrite_u8(f, num_chunks);
-       hashwrite_u8(f, 0); /* unused padding byte */
+               fd = git_mkstemp_mode(ctx->graph_name, 0444);
+               if (fd < 0) {
+                       error(_("unable to create '%s'"), ctx->graph_name);
+                       return -1;
+               }
+
+               f = hashfd(fd, ctx->graph_name);
+       } else {
+               hold_lock_file_for_update(&lk, ctx->graph_name, LOCK_DIE_ON_ERROR);
+               fd = lk.tempfile->fd;
+               f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
+       }
 
        chunk_ids[0] = GRAPH_CHUNKID_OIDFANOUT;
        chunk_ids[1] = GRAPH_CHUNKID_OIDLOOKUP;
        chunk_ids[2] = GRAPH_CHUNKID_DATA;
-       if (ctx->num_extra_edges)
-               chunk_ids[3] = GRAPH_CHUNKID_EXTRAEDGES;
-       else
-               chunk_ids[3] = 0;
-       chunk_ids[4] = 0;
+       if (ctx->num_extra_edges) {
+               chunk_ids[num_chunks] = GRAPH_CHUNKID_EXTRAEDGES;
+               num_chunks++;
+       }
+       if (ctx->num_commit_graphs_after > 1) {
+               chunk_ids[num_chunks] = GRAPH_CHUNKID_BASE;
+               num_chunks++;
+       }
+
+       chunk_ids[num_chunks] = 0;
 
        chunk_offsets[0] = 8 + (num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH;
        chunk_offsets[1] = chunk_offsets[0] + GRAPH_FANOUT_SIZE;
        chunk_offsets[2] = chunk_offsets[1] + hashsz * ctx->commits.nr;
        chunk_offsets[3] = chunk_offsets[2] + (hashsz + 16) * ctx->commits.nr;
-       chunk_offsets[4] = chunk_offsets[3] + 4 * ctx->num_extra_edges;
+
+       num_chunks = 3;
+       if (ctx->num_extra_edges) {
+               chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
+                                               4 * ctx->num_extra_edges;
+               num_chunks++;
+       }
+       if (ctx->num_commit_graphs_after > 1) {
+               chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
+                                               hashsz * (ctx->num_commit_graphs_after - 1);
+               num_chunks++;
+       }
+
+       hashwrite_be32(f, GRAPH_SIGNATURE);
+
+       hashwrite_u8(f, GRAPH_VERSION);
+       hashwrite_u8(f, oid_version());
+       hashwrite_u8(f, num_chunks);
+       hashwrite_u8(f, ctx->num_commit_graphs_after - 1);
 
        for (i = 0; i <= num_chunks; i++) {
                uint32_t chunk_write[3];
@@ -1090,23 +1447,317 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
        write_graph_chunk_data(f, hashsz, ctx);
        if (ctx->num_extra_edges)
                write_graph_chunk_extra_edges(f, ctx);
+       if (ctx->num_commit_graphs_after > 1 &&
+           write_graph_chunk_base(f, ctx)) {
+               return -1;
+       }
        stop_progress(&ctx->progress);
        strbuf_release(&progress_title);
 
+       if (ctx->split && ctx->base_graph_name && ctx->num_commit_graphs_after > 1) {
+               char *new_base_hash = xstrdup(oid_to_hex(&ctx->new_base_graph->oid));
+               char *new_base_name = get_split_graph_filename(ctx->new_base_graph->obj_dir, new_base_hash);
+
+               free(ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 2]);
+               free(ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 2]);
+               ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 2] = new_base_name;
+               ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 2] = new_base_hash;
+       }
+
        close_commit_graph(ctx->r->objects);
-       finalize_hashfile(f, NULL, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
+       finalize_hashfile(f, file_hash.hash, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
+
+       if (ctx->split) {
+               FILE *chainf = fdopen_lock_file(&lk, "w");
+               char *final_graph_name;
+               int result;
+
+               close(fd);
+
+               if (!chainf) {
+                       error(_("unable to open commit-graph chain file"));
+                       return -1;
+               }
+
+               if (ctx->base_graph_name) {
+                       const char *dest = ctx->commit_graph_filenames_after[
+                                               ctx->num_commit_graphs_after - 2];
+
+                       if (strcmp(ctx->base_graph_name, dest)) {
+                               result = rename(ctx->base_graph_name, dest);
+
+                               if (result) {
+                                       error(_("failed to rename base commit-graph file"));
+                                       return -1;
+                               }
+                       }
+               } else {
+                       char *graph_name = get_commit_graph_filename(ctx->obj_dir);
+                       unlink(graph_name);
+               }
+
+               ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1] = xstrdup(oid_to_hex(&file_hash));
+               final_graph_name = get_split_graph_filename(ctx->obj_dir,
+                                       ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1]);
+               ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 1] = final_graph_name;
+
+               result = rename(ctx->graph_name, final_graph_name);
+
+               for (i = 0; i < ctx->num_commit_graphs_after; i++)
+                       fprintf(lk.tempfile->fp, "%s\n", ctx->commit_graph_hash_after[i]);
+
+               if (result) {
+                       error(_("failed to rename temporary commit-graph file"));
+                       return -1;
+               }
+       }
+
        commit_lock_file(&lk);
 
        return 0;
 }
 
+static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
+{
+       struct commit_graph *g = ctx->r->objects->commit_graph;
+       uint32_t num_commits = ctx->commits.nr;
+       uint32_t i;
+
+       int max_commits = 0;
+       int size_mult = 2;
+
+       if (ctx->split_opts) {
+               max_commits = ctx->split_opts->max_commits;
+               size_mult = ctx->split_opts->size_multiple;
+       }
+
+       g = ctx->r->objects->commit_graph;
+       ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;
+
+       while (g && (g->num_commits <= size_mult * num_commits ||
+                   (max_commits && num_commits > max_commits))) {
+               if (strcmp(g->obj_dir, ctx->obj_dir))
+                       break;
+
+               num_commits += g->num_commits;
+               g = g->base_graph;
+
+               ctx->num_commit_graphs_after--;
+       }
+
+       ctx->new_base_graph = g;
+
+       if (ctx->num_commit_graphs_after == 2) {
+               char *old_graph_name = get_commit_graph_filename(g->obj_dir);
+
+               if (!strcmp(g->filename, old_graph_name) &&
+                   strcmp(g->obj_dir, ctx->obj_dir)) {
+                       ctx->num_commit_graphs_after = 1;
+                       ctx->new_base_graph = NULL;
+               }
+
+               free(old_graph_name);
+       }
+
+       ALLOC_ARRAY(ctx->commit_graph_filenames_after, ctx->num_commit_graphs_after);
+       ALLOC_ARRAY(ctx->commit_graph_hash_after, ctx->num_commit_graphs_after);
+
+       for (i = 0; i < ctx->num_commit_graphs_after &&
+                   i < ctx->num_commit_graphs_before; i++)
+               ctx->commit_graph_filenames_after[i] = xstrdup(ctx->commit_graph_filenames_before[i]);
+
+       i = ctx->num_commit_graphs_before - 1;
+       g = ctx->r->objects->commit_graph;
+
+       while (g) {
+               if (i < ctx->num_commit_graphs_after)
+                       ctx->commit_graph_hash_after[i] = xstrdup(oid_to_hex(&g->oid));
+
+               i--;
+               g = g->base_graph;
+       }
+}
+
+static void merge_commit_graph(struct write_commit_graph_context *ctx,
+                              struct commit_graph *g)
+{
+       uint32_t i;
+       uint32_t offset = g->num_commits_in_base;
+
+       ALLOC_GROW(ctx->commits.list, ctx->commits.nr + g->num_commits, ctx->commits.alloc);
+
+       for (i = 0; i < g->num_commits; i++) {
+               struct object_id oid;
+               struct commit *result;
+
+               display_progress(ctx->progress, i + 1);
+
+               load_oid_from_graph(g, i + offset, &oid);
+
+               /* only add commits if they still exist in the repo */
+               result = lookup_commit_reference_gently(ctx->r, &oid, 1);
+
+               if (result) {
+                       ctx->commits.list[ctx->commits.nr] = result;
+                       ctx->commits.nr++;
+               }
+       }
+}
+
+static int commit_compare(const void *_a, const void *_b)
+{
+       const struct commit *a = *(const struct commit **)_a;
+       const struct commit *b = *(const struct commit **)_b;
+       return oidcmp(&a->object.oid, &b->object.oid);
+}
+
+static void sort_and_scan_merged_commits(struct write_commit_graph_context *ctx)
+{
+       uint32_t i, num_parents;
+       struct commit_list *parent;
+
+       if (ctx->report_progress)
+               ctx->progress = start_delayed_progress(
+                                       _("Scanning merged commits"),
+                                       ctx->commits.nr);
+
+       QSORT(ctx->commits.list, ctx->commits.nr, commit_compare);
+
+       ctx->num_extra_edges = 0;
+       for (i = 0; i < ctx->commits.nr; i++) {
+               display_progress(ctx->progress, i);
+
+               if (i && oideq(&ctx->commits.list[i - 1]->object.oid,
+                         &ctx->commits.list[i]->object.oid)) {
+                       die(_("unexpected duplicate commit id %s"),
+                           oid_to_hex(&ctx->commits.list[i]->object.oid));
+               } else {
+                       num_parents = 0;
+                       for (parent = ctx->commits.list[i]->parents; parent; parent = parent->next)
+                               num_parents++;
+
+                       if (num_parents > 2)
+                               ctx->num_extra_edges += num_parents - 1;
+               }
+       }
+
+       stop_progress(&ctx->progress);
+}
+
+static void merge_commit_graphs(struct write_commit_graph_context *ctx)
+{
+       struct commit_graph *g = ctx->r->objects->commit_graph;
+       uint32_t current_graph_number = ctx->num_commit_graphs_before;
+       struct strbuf progress_title = STRBUF_INIT;
+
+       while (g && current_graph_number >= ctx->num_commit_graphs_after) {
+               current_graph_number--;
+
+               if (ctx->report_progress) {
+                       strbuf_addstr(&progress_title, _("Merging commit-graph"));
+                       ctx->progress = start_delayed_progress(progress_title.buf, 0);
+               }
+
+               merge_commit_graph(ctx, g);
+               stop_progress(&ctx->progress);
+               strbuf_release(&progress_title);
+
+               g = g->base_graph;
+       }
+
+       if (g) {
+               ctx->new_base_graph = g;
+               ctx->new_num_commits_in_base = g->num_commits + g->num_commits_in_base;
+       }
+
+       if (ctx->new_base_graph)
+               ctx->base_graph_name = xstrdup(ctx->new_base_graph->filename);
+
+       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;
+       timestamp_t expire_time = time(NULL);
+
+       if (ctx->split_opts && ctx->split_opts->expire_time)
+               expire_time -= ctx->split_opts->expire_time;
+       if (!ctx->split) {
+               char *chain_file_name = get_chain_filename(ctx->obj_dir);
+               unlink(chain_file_name);
+               free(chain_file_name);
+               ctx->num_commit_graphs_after = 0;
+       }
+
+       strbuf_addstr(&path, ctx->obj_dir);
+       strbuf_addstr(&path, "/info/commit-graphs");
+       dir = opendir(path.buf);
+
+       if (!dir)
+               goto out;
+
+       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);
+       }
+
+out:
+       strbuf_release(&path);
+}
+
 int write_commit_graph(const char *obj_dir,
                       struct string_list *pack_indexes,
                       struct string_list *commit_hex,
-                      unsigned int flags)
+                      unsigned int flags,
+                      const struct split_commit_graph_opts *split_opts)
 {
        struct write_commit_graph_context *ctx;
        uint32_t i, count_distinct = 0;
+       size_t len;
        int res = 0;
 
        if (!commit_graph_compatible(the_repository))
@@ -1114,13 +1765,48 @@ int write_commit_graph(const char *obj_dir,
 
        ctx = xcalloc(1, sizeof(struct write_commit_graph_context));
        ctx->r = the_repository;
-       ctx->obj_dir = obj_dir;
+
+       /* normalize object dir with no trailing slash */
+       ctx->obj_dir = xmallocz(strlen(obj_dir) + 1);
+       normalize_path_copy(ctx->obj_dir, obj_dir);
+       len = strlen(ctx->obj_dir);
+       if (len && ctx->obj_dir[len - 1] == '/')
+               ctx->obj_dir[len - 1] = 0;
+
        ctx->append = flags & COMMIT_GRAPH_APPEND ? 1 : 0;
        ctx->report_progress = flags & COMMIT_GRAPH_PROGRESS ? 1 : 0;
+       ctx->split = flags & COMMIT_GRAPH_SPLIT ? 1 : 0;
+       ctx->split_opts = split_opts;
+
+       if (ctx->split) {
+               struct commit_graph *g;
+               prepare_commit_graph(ctx->r);
+
+               g = ctx->r->objects->commit_graph;
+
+               while (g) {
+                       ctx->num_commit_graphs_before++;
+                       g = g->base_graph;
+               }
+
+               if (ctx->num_commit_graphs_before) {
+                       ALLOC_ARRAY(ctx->commit_graph_filenames_before, ctx->num_commit_graphs_before);
+                       i = ctx->num_commit_graphs_before;
+                       g = ctx->r->objects->commit_graph;
+
+                       while (g) {
+                               ctx->commit_graph_filenames_before[--i] = xstrdup(g->filename);
+                               g = g->base_graph;
+                       }
+               }
+       }
 
        ctx->approx_nr_objects = approximate_object_count();
        ctx->oids.alloc = ctx->approx_nr_objects / 32;
 
+       if (ctx->split && split_opts && ctx->oids.alloc > split_opts->max_commits)
+               ctx->oids.alloc = split_opts->max_commits;
+
        if (ctx->append) {
                prepare_commit_graph_one(ctx->r, ctx->obj_dir);
                if (ctx->r->objects->commit_graph)
@@ -1171,14 +1857,45 @@ int write_commit_graph(const char *obj_dir,
                goto cleanup;
        }
 
+       if (!ctx->commits.nr)
+               goto cleanup;
+
+       if (ctx->split) {
+               split_graph_merge_strategy(ctx);
+
+               merge_commit_graphs(ctx);
+       } else
+               ctx->num_commit_graphs_after = 1;
+
        compute_generation_numbers(ctx);
 
        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);
        free(ctx->oids.list);
+       free(ctx->obj_dir);
+
+       if (ctx->commit_graph_filenames_after) {
+               for (i = 0; i < ctx->num_commit_graphs_after; i++) {
+                       free(ctx->commit_graph_filenames_after[i]);
+                       free(ctx->commit_graph_hash_after[i]);
+               }
+
+               for (i = 0; i < ctx->num_commit_graphs_before; i++)
+                       free(ctx->commit_graph_filenames_before[i]);
+
+               free(ctx->commit_graph_filenames_after);
+               free(ctx->commit_graph_filenames_before);
+               free(ctx->commit_graph_hash_after);
+       }
+
        free(ctx);
 
        return res;
@@ -1201,7 +1918,7 @@ static void graph_report(const char *fmt, ...)
 #define GENERATION_ZERO_EXISTS 1
 #define GENERATION_NUMBER_EXISTS 2
 
-int verify_commit_graph(struct repository *r, struct commit_graph *g)
+int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags)
 {
        uint32_t i, cur_fanout_pos = 0;
        struct object_id prev_oid, cur_oid, checksum;
@@ -1209,6 +1926,7 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g)
        struct hashfile *f;
        int devnull;
        struct progress *progress = NULL;
+       int local_error = 0;
 
        if (!g) {
                graph_report("no commit-graph file loaded");
@@ -1303,6 +2021,9 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g)
                                break;
                        }
 
+                       /* parse parent in case it is in a base graph */
+                       parse_commit_in_graph_one(r, g, graph_parents->item);
+
                        if (!oideq(&graph_parents->item->object.oid, &odb_parents->item->object.oid))
                                graph_report(_("commit-graph parent for %s is %s != %s"),
                                             oid_to_hex(&cur_oid),
@@ -1354,7 +2075,12 @@ int verify_commit_graph(struct repository *r, struct commit_graph *g)
        }
        stop_progress(&progress);
 
-       return verify_commit_graph_error;
+       local_error = verify_commit_graph_error;
+
+       if (!(flags & COMMIT_GRAPH_VERIFY_SHALLOW) && g->base_graph)
+               local_error |= verify_commit_graph(r, g->base_graph, flags);
+
+       return local_error;
 }
 
 void free_commit_graph(struct commit_graph *g)
@@ -1366,5 +2092,6 @@ void free_commit_graph(struct commit_graph *g)
                g->data = NULL;
                close(g->graph_fd);
        }
+       free(g->filename);
        free(g);
 }