# [PATCH] handle concurrent pruning of packed objects 7 messages from 2006-06-02 to 2006-06-02. Participants: Jeff King, Junio C Hamano, Linus Torvalds. Thread: https://gitlist.dev/t/4375 ## Jeff King, 2006-06-02 15:32 Subject: [PATCH] handle concurrent pruning of packed objects Message-ID: <20060602153223.GA4223@coredump.intra.peff.net> URL: https://gitlist.dev/e/20060602153223.GA4223%40coredump.intra.peff.net ``` This patch causes read_sha1_file and sha1_object_info to re-examine the list of packs if an object cannot be found. It works by re-running prepare_packed_git() after an object fails to be found. It does not attempt to clean up the old pack list. Old packs which are in use can continue to be used (until unused by lru selection). New packs are placed at the front of the list and will thus be examined before old packs. Signed-off-by: Jeff King --- This is a repost, since there was no response last time. Linus indicated this approach was reasonable; see: I tested this by making a simple repo with three commits: a, b, and c. I ran git diff-tree --stdin, and then did the following: 1. fed 'a b' to diff-tree 2. ran git repack -a -d 3. fed 'b c' to diff-tree Vanilla git complains about the lack of object, whereas this version provides the correct diff-tree output. sha1_file.c | 24 ++++++++++++++++++------ 1 files changed, 18 insertions(+), 6 deletions(-) diff --git a/sha1_file.c b/sha1_file.c index f77c189..696e53f 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -626,12 +626,12 @@ static void prepare_packed_git_one(char closedir(dir); } +static int prepare_packed_git_run_once = 0; void prepare_packed_git(void) { - static int run_once = 0; struct alternate_object_database *alt; - if (run_once) + if (prepare_packed_git_run_once) return; prepare_packed_git_one(get_object_directory(), 1); prepare_alt_odb(); @@ -640,7 +640,13 @@ void prepare_packed_git(void) prepare_packed_git_one(alt->base, 0); alt->name[-1] = '/'; } - run_once = 1; + prepare_packed_git_run_once = 1; +} + +static void reprepare_packed_git(void) +{ + prepare_packed_git_run_once = 0; + prepare_packed_git(); } int check_sha1_signature(const unsigned char *sha1, void *map, unsigned long size, const char *type) @@ -1212,9 +1218,12 @@ int sha1_object_info(const unsigned char if (!map) { struct pack_entry e; - if (!find_pack_entry(sha1, &e)) - return error("unable to find %s", sha1_to_hex(sha1)); - return packed_object_info(&e, type, sizep); + if (find_pack_entry(sha1, &e)) + return packed_object_info(&e, type, sizep); + reprepare_packed_git(); + if (find_pack_entry(sha1, &e)) + return packed_object_info(&e, type, sizep); + return error("unable to find %s", sha1_to_hex(sha1)); } if (unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr)) < 0) status = error("unable to unpack %s header", @@ -1256,6 +1265,9 @@ void * read_sha1_file(const unsigned cha munmap(map, mapsize); return buf; } + reprepare_packed_git(); + if (find_pack_entry(sha1, &e)) + return read_packed_sha1(sha1, type, size); return NULL; } -- 1.3.3.g331f - To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html ----- End forwarded message ----- ``` ## Junio C Hamano, 2006-06-02 15:53 Subject: Re: [PATCH] handle concurrent pruning of packed objects Message-ID: <7vwtbzblkf.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7vwtbzblkf.fsf%40assigned-by-dhcp.cox.net In-Reply-To: <20060602153223.GA4223@coredump.intra.peff.net> ``` Jeff King writes: > This is a repost, since there was no response last time. Linus > indicated this approach was reasonable; see: > I haven't forgotten about it, but I have been sick. I am uncertain about not re-examining the packs it originally thought it had. By prepending the new ones (and the same old surviving ones) at the beginning you are effectively hiding the old packs, which sounds reasonable in the usual case. Also I suspect this might have funny interaction with the case where there are hand-added packs (see how verify-pack does it). We do not silently "fix" missing object problems we discover there. ``` ## Junio C Hamano, 2006-06-02 16:03 Subject: Re: [PATCH] handle concurrent pruning of packed objects Message-ID: <7vodxbbl4p.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7vodxbbl4p.fsf%40assigned-by-dhcp.cox.net In-Reply-To: <7vwtbzblkf.fsf@assigned-by-dhcp.cox.net> ``` Junio C Hamano writes: > Also I suspect this might have funny interaction with the case > where there are hand-added packs (see how verify-pack does it). > We do not silently "fix" missing object problems we discover > there. The last sentence should read 'We do not want to silently...'. Sorry. ``` ## Jeff King, 2006-06-02 16:04 Subject: Re: [PATCH] handle concurrent pruning of packed objects Message-ID: <20060602160456.GA8957@coredump.intra.peff.net> URL: https://gitlist.dev/e/20060602160456.GA8957%40coredump.intra.peff.net In-Reply-To: <7vwtbzblkf.fsf@assigned-by-dhcp.cox.net> ``` On Fri, Jun 02, 2006 at 08:53:52AM -0700, Junio C Hamano wrote: > I am uncertain about not re-examining the packs it originally > thought it had. By prepending the new ones (and the same old > surviving ones) at the beginning you are effectively hiding the > old packs, which sounds reasonable in the usual case. That shouldn't make a difference for correctness, even if the old packs are still there. If you have an object in two packs, then it doesn't matter which one you pull it from. The main impacts I can think of are: 1. The old pack may already be mapped, and it would be more efficient to use it. However, the new pack will be mapped on first use, so it will be used from then on. 2. The pack list can grow without bound. However, for this to matter, you'd have to do many prunes during the course of a single git command. > Also I suspect this might have funny interaction with the case > where there are hand-added packs (see how verify-pack does it). > We do not silently "fix" missing object problems we discover > there. I will take a look at this. -Peff ``` ## Junio C Hamano, 2006-06-02 16:10 Subject: Re: [PATCH] handle concurrent pruning of packed objects Message-ID: <7vk67zbksv.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7vk67zbksv.fsf%40assigned-by-dhcp.cox.net In-Reply-To: <20060602160456.GA8957@coredump.intra.peff.net> ``` Jeff King writes: > That shouldn't make a difference for correctness, even if the old packs > are still there. If you have an object in two packs, then it doesn't > matter which one you pull it from. The main impacts I can think of are: > 1. The old pack may already be mapped, and it would be more efficient > to use it. However, the new pack will be mapped on first use, so it > will be used from then on. > 2. The pack list can grow without bound. However, for this to matter, > you'd have to do many prunes during the course of a single git > command. I agree 100% on "shouldn't" part. What I wonder is if everybody works correctly if we mmap the same file (all available .idx are mapped all the time, and we map .pack LRU) twice. But I realize we have NO_MMAP configuration for unfortunate platforms to work it around so that wouldn't be a big deal. ``` ## Jeff King, 2006-06-02 16:49 Subject: [PATCH] sha1_file: avoid re-preparing duplicate packs Message-ID: <20060602164932.GA10216@coredump.intra.peff.net> URL: https://gitlist.dev/e/20060602164932.GA10216%40coredump.intra.peff.net In-Reply-To: <7vk67zbksv.fsf@assigned-by-dhcp.cox.net> ``` When adding packs, skip the pack if we already have it in the packed_git list. This might happen if we are re-preparing our packs because of a missing object. --- On Fri, Jun 02, 2006 at 09:10:24AM -0700, Junio C Hamano wrote: > I agree 100% on "shouldn't" part. What I wonder is if everybody > works correctly if we mmap the same file (all available .idx are This patch avoids duplicates in the packed_git list. It's not necessary under Linux, at least, but it just seems cleaner, and it's simple to do. The list might still have packs that are now gone. I didn't want to purge anything from the packed_git list since I'm not clear on whether other code might have pointers into the mmap'd portion. sha1_file.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/sha1_file.c b/sha1_file.c index 696e53f..aea0f40 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -617,6 +617,12 @@ static void prepare_packed_git_one(char /* we have .idx. Is it a file we can map? */ strcpy(path + len, de->d_name); + for (p = packed_git; p; p = p->next) { + if (!memcmp(path, p->pack_name, len + namelen - 4)) + break; + } + if (p) + continue; p = add_packed_git(path, len + namelen, local); if (!p) continue; -- 1.3.3.gfb825 ``` ## Linus Torvalds, 2006-06-02 17:47 Subject: Re: [PATCH] sha1_file: avoid re-preparing duplicate packs Message-ID: URL: https://gitlist.dev/e/Pine.LNX.4.64.0606021045580.5498%40g5.osdl.org In-Reply-To: <20060602164932.GA10216@coredump.intra.peff.net> ``` On Fri, 2 Jun 2006, Jeff King wrote: > > This patch avoids duplicates in the packed_git list. It's not necessary > under Linux, at least, but it just seems cleaner, and it's simple to do. I think it's a good idea even under Linux, since on 32-bit machines, one of the constraints we have may simply be virtual memory space to map things into. With big packs, avoiding mapping them twice is a good idea. Linus ```