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 --- midx.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) (limited to 'midx.c') diff --git a/midx.c b/midx.c index 8b8faec35a..e7e1fe4d65 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) -- cgit v1.3-5-g9baa