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 --- object-store.h | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) (limited to 'object-store.h') diff --git a/object-store.h b/object-store.h index b086f5ecdb..7acbc7fffe 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" */ @@ -128,12 +129,6 @@ struct raw_object_store { /* A most-recently-used ordered version of the packed_git list. */ 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 -- cgit v1.3