From af96fe3392fb078cb5447bcb94f2ed8d79d0a4a8 Mon Sep 17 00:00:00 2001 From: Derrick Stolee Date: Mon, 29 Apr 2019 09:18:56 -0700 Subject: midx: add packs to packed_git linked list The multi-pack-index allows searching for objects across multiple packs using one object list. The original design gains many of these performance benefits by keeping the packs in the multi-pack-index out of the packed_git list. Unfortunately, this has one major drawback. If the multi-pack-index covers thousands of packs, and a command loads many of those packs, then we can hit the limit for open file descriptors. The close_one_pack() method is used to limit this resource, but it only looks at the packed_git list, and uses an LRU cache to prevent thrashing. Instead of complicating this close_one_pack() logic to include direct references to the multi-pack-index, simply add the packs opened by the multi-pack-index to the packed_git list. This immediately solves the file-descriptor limit problem, but requires some extra steps to avoid performance issues or other problems: 1. Create a multi_pack_index bit in the packed_git struct that is one if and only if the pack was loaded from a multi-pack-index. 2. Skip packs with the multi_pack_index bit when doing object lookups and abbreviations. These algorithms already check the multi-pack-index before the packed_git struct. This has a very small performance hit, as we need to walk more packed_git structs. This is acceptable, since these operations run binary search on the other packs, so this walk-and-ignore logic is very fast by comparison. 3. When closing a multi-pack-index file, do not close its packs, as those packs will be closed using close_all_packs(). In some cases, such as 'git repack', we run 'close_midx()' without also closing the packs, so we need to un-set the multi_pack_index bit in those packs. This is necessary, and caught by running t6501-freshen-objects.sh with GIT_TEST_MULTI_PACK_INDEX=1. To manually test this change, I inserted trace2 logging into close_pack_fd() and set pack_max_fds to 10, then ran 'git rev-list --all --objects' on a copy of the Git repo with 300+ pack-files and a multi-pack-index. The logs verified the packs are closed as we read them beyond the file descriptor limit. Signed-off-by: Derrick Stolee Signed-off-by: Junio C Hamano diff --git a/midx.c b/midx.c index 8b8faec..e7e1fe4 100644 --- a/midx.c +++ b/midx.c @@ -192,10 +192,8 @@ void close_midx(struct multi_pack_index *m) m->fd = -1; for (i = 0; i < m->num_packs; i++) { - if (m->packs[i]) { - close_pack(m->packs[i]); - free(m->packs[i]); - } + if (m->packs[i]) + m->packs[i]->multi_pack_index = 0; } FREE_AND_NULL(m->packs); FREE_AND_NULL(m->pack_names); @@ -204,6 +202,7 @@ void close_midx(struct multi_pack_index *m) int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id) { struct strbuf pack_name = STRBUF_INIT; + struct packed_git *p; if (pack_int_id >= m->num_packs) die(_("bad pack-int-id: %u (%u total packs)"), @@ -215,9 +214,18 @@ int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t strbuf_addf(&pack_name, "%s/pack/%s", m->object_dir, m->pack_names[pack_int_id]); - m->packs[pack_int_id] = add_packed_git(pack_name.buf, pack_name.len, m->local); + p = add_packed_git(pack_name.buf, pack_name.len, m->local); strbuf_release(&pack_name); - return !m->packs[pack_int_id]; + + if (!p) + return 1; + + p->multi_pack_index = 1; + m->packs[pack_int_id] = p; + install_packed_git(r, p); + list_add_tail(&p->mru, &r->objects->packed_git_mru); + + return 0; } int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result) diff --git a/object-store.h b/object-store.h index b086f5e..7acbc7f 100644 --- a/object-store.h +++ b/object-store.h @@ -76,7 +76,8 @@ struct packed_git { pack_keep_in_core:1, freshened:1, do_not_close:1, - pack_promisor:1; + pack_promisor:1, + multi_pack_index:1; unsigned char hash[GIT_MAX_RAWSZ]; struct revindex_entry *revindex; /* something like ".git/objects/pack/xxxxx.pack" */ @@ -129,12 +130,6 @@ struct raw_object_store { struct list_head packed_git_mru; /* - * A linked list containing all packfiles, starting with those - * contained in the multi_pack_index. - */ - struct packed_git *all_packs; - - /* * A fast, rough count of the number of objects in the repository. * These two fields are not meant for direct access. Use * approximate_object_count() instead. diff --git a/packfile.c b/packfile.c index 7b94a14..060de42 100644 --- a/packfile.c +++ b/packfile.c @@ -994,8 +994,6 @@ static void prepare_packed_git(struct repository *r) } rearrange_packed_git(r); - r->objects->all_packs = NULL; - prepare_packed_git_mru(r); r->objects->packed_git_initialized = 1; } @@ -1026,26 +1024,16 @@ struct multi_pack_index *get_multi_pack_index(struct repository *r) struct packed_git *get_all_packs(struct repository *r) { - prepare_packed_git(r); - - if (!r->objects->all_packs) { - struct packed_git *p = r->objects->packed_git; - struct multi_pack_index *m; - - for (m = r->objects->multi_pack_index; m; m = m->next) { - uint32_t i; - for (i = 0; i < m->num_packs; i++) { - if (!prepare_midx_pack(r, m, i)) { - m->packs[i]->next = p; - p = m->packs[i]; - } - } - } + struct multi_pack_index *m; - r->objects->all_packs = p; + prepare_packed_git(r); + for (m = r->objects->multi_pack_index; m; m = m->next) { + uint32_t i; + for (i = 0; i < m->num_packs; i++) + prepare_midx_pack(r, m, i); } - return r->objects->all_packs; + return r->objects->packed_git; } struct list_head *get_packed_git_mru(struct repository *r) @@ -2004,7 +1992,7 @@ int find_pack_entry(struct repository *r, const struct object_id *oid, struct pa list_for_each(pos, &r->objects->packed_git_mru) { struct packed_git *p = list_entry(pos, struct packed_git, mru); - if (fill_pack_entry(oid, e, p)) { + if (!p->multi_pack_index && fill_pack_entry(oid, e, p)) { list_move(&p->mru, &r->objects->packed_git_mru); return 1; } diff --git a/sha1-name.c b/sha1-name.c index 07c71a7..42ac1c5 100644 --- a/sha1-name.c +++ b/sha1-name.c @@ -157,6 +157,9 @@ static void unique_in_pack(struct packed_git *p, uint32_t num, i, first = 0; const struct object_id *current = NULL; + if (p->multi_pack_index) + return; + if (open_pack_index(p) || !p->num_objects) return; @@ -589,6 +592,9 @@ static void find_abbrev_len_for_pack(struct packed_git *p, struct object_id oid; const struct object_id *mad_oid; + if (p->multi_pack_index) + return; + if (open_pack_index(p) || !p->num_objects) return; -- cgit v0.10.2-6-g49f6