# Poor performance of git describe in big repos 33 messages from 2013-05-30 to 2013-06-03. Participants: Alex Bennée, Ramkumar Ramachandra, John Keeping, Duy Nguyen, Thomas Rast, Antoine Pelisse, Jeff King, Junio C Hamano. Thread: https://gitlist.dev/t/33984 ## Alex Bennée, 2013-05-30 10:38 Subject: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NPQLVFhtb9KMLNLc5MqguBYM1%3DgKEVrrtT3kSMiZKma_g%40mail.gmail.com ``` Hi, I'm a fairly heavy user of the magit Emacs extension for interacting with my git repos. However I've noticed there are some cases where lag is very high. By analysing strace output of emacs calling git I found two commands that where particularly problematic when interrogating the repo: 11:00 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --long --tags ajb-build-test-5224-10-gfa296e6 real 0m5.016s user 0m4.364s sys 0m0.444s 11:34 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --contains HEAD fatal: cannot describe 'fa296e61f549a1252a65a13b2f734d7afbc7e88e' real 0m4.805s user 0m4.388s sys 0m0.400s Running with first command with the --debug flag on gives: 11:34 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --long --tags --debug searching to describe HEAD lightweight 10 ajb-build-test-5224 lightweight 41 ajb-build-test-5222 annotated 146 vnms-2-1-36-32 annotated 155 vnms-2-1-36-31 annotated 174 vnms-2-1-36-30 annotated 183 vnms-2-1-36-29 lightweight 188 vnms-2-1-36-28 annotated 193 vnms-2-1-36-27 annotated 206 vnms-2-1-36-26 annotated 215 vectastar-4-2-83-5 traversed 223 commits more than 10 tags found; listed 10 most recent gave up search at 2b69df72d47be8440e3ce4cee91b9b7ceaf8b77c ajb-build-test-5224-10-gfa296e6 real 0m4.817s user 0m4.320s sys 0m0.464s Which has only traversed 223 before coming to a decision. This seems like a very low number of commits given the time it's spent doing this. One factor might be the size of my repo (.git is around 2.4G). Could this just be due to computational cost of searching through large packs to walk the commit chain? Is there any way to make this easier for git to do? -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Ramkumar Ramachandra, 2013-05-30 11:33 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CALkWK0ndKMZRuWgdg6djqPUGxbDAqZPcv2q0qPrv_2b%3D1NEM5g%40mail.gmail.com In-Reply-To: ``` Alex Bennée wrote: >>time /usr/bin/git --no-pager > traversed 223 commits > > real 0m4.817s > user 0m4.320s > sys 0m0.464s I'm quite clueless about why it is taking this long: I think it's IO because there's nothing to compute? I really can't trace anything unless you can reproduce it on a public repository. On linux.git with my rotating hard disk: $ time git describe --debug --long --tags HEAD~10000 searching to describe HEAD~10000 annotated 5445 v2.6.33 annotated 5660 v2.6.33-rc8 annotated 5884 v2.6.33-rc7 annotated 6140 v2.6.33-rc6 annotated 6467 v2.6.33-rc5 annotated 6999 v2.6.33-rc4 annotated 7430 v2.6.33-rc3 annotated 7746 v2.6.33-rc2 annotated 8212 v2.6.33-rc1 annotated 13854 v2.6.32 traversed 18895 commits more than 10 tags found; listed 10 most recent gave up search at 648f4e3e50c4793d9dbf9a09afa193631f76fa26 v2.6.33-5445-ge7c84ee real 0m0.509s user 0m0.470s sys 0m0.037s 18k+ commits traversed in half a second here, so I really don't know what is going on. ``` ## John Keeping, 2013-05-30 11:48 Subject: Re: Poor performance of git describe in big repos Message-ID: <20130530114808.GD17475@serenity.lan> URL: https://gitlist.dev/e/20130530114808.GD17475%40serenity.lan In-Reply-To: ``` On Thu, May 30, 2013 at 11:38:32AM +0100, Alex Bennée wrote: > One factor might be the size of my repo (.git is around 2.4G). Could > this just be due to computational cost of searching through large > packs to walk the commit chain? Is there any way to make this easier > for git to do? What does "git count-objects -v" say for your repository? You may find that performance improves if you repack with "git gc --aggressive". ``` ## Alex Bennée, 2013-05-30 12:29 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NM9EhikDBP0izqWrnLbZW6RcHq_cH-20YTE08SZw5fjqA%40mail.gmail.com In-Reply-To: <20130530114808.GD17475@serenity.lan> ``` The repo is a fairly hairy one as it includes two historically un-related but content related repos which I'm the process of cherry-picking stuff across. 11:58 ajb@sloy/x86_64 [work.git] >git count-objects -v count: 493 size: 4572 in-pack: 399307 packs: 1 size-pack: 1930755 prune-packable: 0 garbage: 0 size-garbage: 0 This was after a repack which did have slight negative effect on performance. The pack file is: 13:27 ajb@sloy/x86_64 [work.git] >ls -lh ./.git/objects/pack/* -r--r--r-- 1 ajb cvs 11M May 30 11:56 ./.git/objects/pack/pack-a9ba133a6f25ffa74c3c407e09ab030f8745b201.idx -r--r--r-- 1 ajb cvs 1.9G May 30 11:56 ./.git/objects/pack/pack-a9ba133a6f25ffa74c3c407e09ab030f8745b201.pack I ran perf on it and the top items in the report where: 41.58% git libcrypto.so.1.0.0 [.] 0x6ae73 33.96% git libz.so.1.2.3.4 [.] 0xe0ec 10.39% git libz.so.1.2.3.4 [.] adler32 2.03% git [kernel.kallsyms] [k] clear_page_c So I'm guessing it's spending a lot of non-cache efficient time un-packing and processing the deltas? -- Alex. On 30 May 2013 12:48, John Keeping wrote: > On Thu, May 30, 2013 at 11:38:32AM +0100, Alex Bennée wrote: >> One factor might be the size of my repo (.git is around 2.4G). Could >> this just be due to computational cost of searching through large >> packs to walk the commit chain? Is there any way to make this easier >> for git to do? > > What does "git count-objects -v" say for your repository? > > You may find that performance improves if you repack with "git gc > --aggressive". -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Alex Bennée, 2013-05-30 13:09 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NNAeLUfyk8%2BNU8PmjKqfTcZ1NT_NPAk3M1QROtzsQKJ8g%40mail.gmail.com In-Reply-To: ``` It looks like it's a file caching effect combined with my repo being more pathalogical in size and contents. Note run 1 (cold) vs run 2 on the linux file tree: 13:52 ajb@sloy/x86_64 [linux.git] >time git describe --debug --long --tags HEAD~10000 searching to describe HEAD~10000 annotated 57 v2.6.34-rc2 annotated 1688 v2.6.34-rc1 annotated 7932 v2.6.33 annotated 8157 v2.6.33-rc8 annotated 8381 v2.6.33-rc7 annotated 8637 v2.6.33-rc6 annotated 8964 v2.6.33-rc5 annotated 9493 v2.6.33-rc4 annotated 9912 v2.6.33-rc3 annotated 10202 v2.6.33-rc2 traversed 10547 commits more than 10 tags found; listed 10 most recent gave up search at 55639353a0035052d9ea6cfe4dde0ac7fcbb2c9f v2.6.34-rc2-57-gef5da59 real 0m7.332s user 0m0.308s sys 0m0.244s 14:03 ajb@sloy/x86_64 [linux.git] >time git describe --debug --long --tags HEAD~10000 searching to describe HEAD~10000 annotated 57 v2.6.34-rc2 annotated 1688 v2.6.34-rc1 annotated 7932 v2.6.33 annotated 8157 v2.6.33-rc8 annotated 8381 v2.6.33-rc7 annotated 8637 v2.6.33-rc6 annotated 8964 v2.6.33-rc5 annotated 9493 v2.6.33-rc4 annotated 9912 v2.6.33-rc3 annotated 10202 v2.6.33-rc2 traversed 10547 commits more than 10 tags found; listed 10 most recent gave up search at 55639353a0035052d9ea6cfe4dde0ac7fcbb2c9f v2.6.34-rc2-57-gef5da59 real 0m0.298s user 0m0.244s sys 0m0.036s Although the perf profile looks subtly different. First through the linux tree: 22.35% git libz.so.1.2.3.4 [.] inflate 18.56% git libz.so.1.2.3.4 [.] inflate_fast 17.48% git libz.so.1.2.3.4 [.] inflate_table 7.84% git git [.] hashcmp 3.93% git git [.] get_sha1_hex 3.46% git libz.so.1.2.3.4 [.] adler32 And through my "special" repo: 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 33.62% git libz.so.1.2.3.4 [.] inflate_fast 10.39% git libz.so.1.2.3.4 [.] adler32 2.03% git [kernel.kallsyms] [k] clear_page_c I'm not sure why libcrypto features so highly in the results -- Alex. On 30 May 2013 12:33, Ramkumar Ramachandra wrote: > Alex Bennée wrote: >>>time /usr/bin/git --no-pager >> traversed 223 commits >> >> real 0m4.817s >> user 0m4.320s >> sys 0m0.464s > > I'm quite clueless about why it is taking this long: I think it's IO > because there's nothing to compute? I really can't trace anything > unless you can reproduce it on a public repository. On linux.git with > my rotating hard disk: > > $ time git describe --debug --long --tags HEAD~10000 > searching to describe HEAD~10000 > annotated 5445 v2.6.33 > annotated 5660 v2.6.33-rc8 > annotated 5884 v2.6.33-rc7 > annotated 6140 v2.6.33-rc6 > annotated 6467 v2.6.33-rc5 > annotated 6999 v2.6.33-rc4 > annotated 7430 v2.6.33-rc3 > annotated 7746 v2.6.33-rc2 > annotated 8212 v2.6.33-rc1 > annotated 13854 v2.6.32 > traversed 18895 commits > more than 10 tags found; listed 10 most recent > gave up search at 648f4e3e50c4793d9dbf9a09afa193631f76fa26 > v2.6.33-5445-ge7c84ee > > real 0m0.509s > user 0m0.470s > sys 0m0.037s > > 18k+ commits traversed in half a second here, so I really don't know > what is going on. -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Alex Bennée, 2013-05-30 13:16 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NOyQu7pfY7jwKTJ2ZS_h9pBtnyeMAxJVzjC7R0kVoLUBw%40mail.gmail.com In-Reply-To: <20130530114808.GD17475@serenity.lan> ``` > You may find that performance improves if you repack with "git gc --aggressive". It seems that increases the time to get to where it wants to: 14:12 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --long --tags --debug searching to describe HEAD lightweight 10 ajb-build-test-5224 lightweight 41 ajb-build-test-5222 annotated 146 vnms-2-1-36-32 annotated 155 vnms-2-1-36-31 annotated 174 vnms-2-1-36-30 annotated 183 vnms-2-1-36-29 lightweight 188 vnms-2-1-36-28 annotated 193 vnms-2-1-36-27 annotated 206 vnms-2-1-36-26 annotated 215 vectastar-4-2-83-5 traversed 223 commits more than 10 tags found; listed 10 most recent gave up search at 2b69df72d47be8440e3ce4cee91b9b7ceaf8b77c ajb-build-test-5224-10-gfa296e6 real 0m14.658s user 0m12.845s sys 0m1.776s On 30 May 2013 12:48, John Keeping wrote: > On Thu, May 30, 2013 at 11:38:32AM +0100, Alex Bennée wrote: >> One factor might be the size of my repo (.git is around 2.4G). Could >> this just be due to computational cost of searching through large >> packs to walk the commit chain? Is there any way to make this easier >> for git to do? > > What does "git count-objects -v" say for your repository? > > You may find that performance improves if you repack with "git gc > --aggressive". -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Duy Nguyen, 2013-05-30 13:20 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CACsJy8A1oEezNeFjXTrQ%3D%2BgJ6nxDheFYTU0xtiSRt0aOOvE%3DVw%40mail.gmail.com In-Reply-To: ``` On Thu, May 30, 2013 at 7:29 PM, Alex Bennée wrote: > I ran perf on it and the top items in the report where: > > 41.58% git libcrypto.so.1.0.0 [.] 0x6ae73 > 33.96% git libz.so.1.2.3.4 [.] 0xe0ec > 10.39% git libz.so.1.2.3.4 [.] adler32 > 2.03% git [kernel.kallsyms] [k] clear_page_c > > So I'm guessing it's spending a lot of non-cache efficient time > un-packing and processing the deltas? If I'm not mistaken, commits are never deltified. They are usually small and packed close together for better I/O patterns. If you really just read hundreds of commits, it can't take that long. Maybe some code paths accidentally open a tree, a blob or something.. Can you try setting core.logpackaccess to a path on and rerun describe? Jugding from the code (I never actually tried it), it'll create a file at the given path with the accessed pack offsets. You can check what offset corresponds to what object with verify-pack -v. -- Duy ``` ## Duy Nguyen, 2013-05-30 13:45 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CACsJy8AuhbwkjGjeQRYe1XZFsAntNdpKYxBM9aeMwF3HpB16Ow%40mail.gmail.com In-Reply-To: ``` On Thu, May 30, 2013 at 8:34 PM, Alex Bennée wrote: > From the following run: > > > 14:31 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager > describe --long --tags > ajb-build-test-5224-11-g9660048 > > real 0m14.720s > user 0m12.985s > sys 0m1.700s > 14:31 ajb@sloy/x86_64 [work.git] >wc -l /tmp/log-pack.txt > 1610 /tmp/log-pack.txt > > The pack has been "tuned" with a gc --aggressive. Assuming the numbers > are offsets into the pack it looks fairly random access until the last > 100 or so. > > [snipped] Thanks. Can you share "verify-pack -v" output of pack-a9ba133a6f25ffa74c3c407e09ab030f8745b201.pack? I think you need to put it somewhere on Internet temporarily as it's likely to exceed git@vger limits. -- Duy ``` ## Alex Bennée, 2013-05-30 14:02 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NNB7b5Bgc4B5OUOta%2BQ08%2BfgKf_NzuG44z8_teqWgnctQ%40mail.gmail.com In-Reply-To: ``` On 30 May 2013 14:45, Duy Nguyen wrote: > On Thu, May 30, 2013 at 8:34 PM, Alex Bennée wrote: > > Thanks. Can you share "verify-pack -v" output of > pack-a9ba133a6f25ffa74c3c407e09ab030f8745b201.pack? I think you need > to put it somewhere on Internet temporarily as it's likely to exceed > git@vger limits. > -- > Duy http://www.bennee.com/~alex/stuff/git-pack-access.tar.bz2 -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Ramkumar Ramachandra, 2013-05-30 14:32 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CALkWK0%3DbgM%2BfYcVEwjHHF8k2Q8wMmjdbM5bxXdPH6s9StDH_Ng%40mail.gmail.com In-Reply-To: ``` Alex Bennée wrote: > And through my "special" repo: > > 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 > 33.62% git libz.so.1.2.3.4 [.] inflate_fast > 10.39% git libz.so.1.2.3.4 [.] adler32 > 2.03% git [kernel.kallsyms] [k] clear_page_c > > I'm not sure why libcrypto features so highly in the results While Duy churns on the delta chain, let me try to make a (rather crude) observation: What does it mean for libcrypto to be so high in your perf report? sha1_block_data_order is ultimately by object.c:parse_object. While it indicates that deltas are taking a long time to apply (or are somehow not optimally organized for IO), I think it indicates either: 1. Your history is very deep and there are an unusually high number of deltas for each blob. What are the total number of commits? 2. You have have huge (binary) files checked into your repository. Do you? If so, why isn't the code in streaming.c kicking in? ``` ## Alex Bennée, 2013-05-30 15:01 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NMt6h%3DJFLLCP%2BLASKMcToENhF%3DBSsk1dPML0024hJTwTw%40mail.gmail.com In-Reply-To: ``` On 30 May 2013 15:32, Ramkumar Ramachandra wrote: > Alex Bennée wrote: >> And through my "special" repo: >> >> 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 >> 33.62% git libz.so.1.2.3.4 [.] inflate_fast >> 10.39% git libz.so.1.2.3.4 [.] adler32 >> 2.03% git [kernel.kallsyms] [k] clear_page_c >> >> I'm not sure why libcrypto features so highly in the results > > While Duy churns on the delta chain, let me try to make a (rather > crude) observation: > > What does it mean for libcrypto to be so high in your perf report? > sha1_block_data_order is ultimately by object.c:parse_object. While > it indicates that deltas are taking a long time to apply (or are > somehow not optimally organized for IO), I think it indicates either: > > 1. Your history is very deep and there are an unusually high number of > deltas for each blob. What are the total number of commits? Well the history does en-compose about 10 years of product development and has a high number of files in the repo (including about 3 copies of the kernel - sans upstream history). 15:50 ajb@sloy/x86_64 [work.git] >time git log --pretty=oneline | wc -l 24648 real 0m0.434s user 0m0.388s sys 0m0.112s Although it doesn't take too long to walk the whole mainline history (obviously ignoring all the other branches). 15:52 ajb@sloy/x86_64 [work.git] >git count-objects -v -H count: 581 size: 5.09 MiB in-pack: 399307 packs: 1 size-pack: 1.49 GiB prune-packable: 0 garbage: 0 size-garbage: 0 bytes It is a pick repo. The gc --aggressive nearly took out my machine keeping around 4gb resident for most of the half hour and using nearly 8gb of VM. Of course most of the history is not needed for day to day stuff. Maybe if I split the pack files up it wouldn't be quite such a strain to work through them? > 2. You have have huge (binary) files checked into your repository. Do > you? If so, why isn't the code in streaming.c kicking in? We do have some binary blobs in the repository (mainly DSP and FPGA images) although not a huge number: 15:58 ajb@sloy/x86_64 [work.git] >time git log --pretty=oneline -- xxx xxx/xxxxxx/*.out ./xxx/xxx/*.out ./xxx/xxxxxxx/*.out | wc -l 234 real 0m0.590s user 0m0.552s sys 0m0.040s How can I tell if streaming is kicking in or now? -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Ramkumar Ramachandra, 2013-05-30 15:17 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CALkWK0%3D6xg8X7ZLXoaTk_ZgRnhgXWsftsTzr6JAWFBJvmVOgFw%40mail.gmail.com In-Reply-To: ``` Alex Bennée wrote: > 15:50 ajb@sloy/x86_64 [work.git] >time git log --pretty=oneline | wc -l > 24648 > > real 0m0.434s > user 0m0.388s > sys 0m0.112s > > Although it doesn't take too long to walk the whole mainline history > (obviously ignoring all the other branches). Damn, non-starter. linux.git has 361k+ commits in mainline history. Nit: use git rev-list --count HEAD next time. > 15:52 ajb@sloy/x86_64 [work.git] >git count-objects -v -H > count: 581 > size: 5.09 MiB > in-pack: 399307 > packs: 1 > size-pack: 1.49 GiB > prune-packable: 0 > garbage: 0 > size-garbage: 0 bytes linux.git has 2.9m+ in-pack. The pack-size is much lower at about 800+ MiB, but I don't think 1.49 GiB is a problem in itself. Looking forward to your big-files report to see why it's so big. > It is a pick repo. The gc --aggressive nearly took out my machine keeping > around 4gb resident for most of the half hour and using nearly 8gb of VM. > > Of course most of the history is not needed for day to day stuff. Maybe > if I split the pack files up it wouldn't be quite such a strain to work > through them? Really out of my depth here, sorry. Let's see what Duy (or the others) have to say. >> 2. You have have huge (binary) files checked into your repository. Do >> you? If so, why isn't the code in streaming.c kicking in? > > We do have some binary blobs in the repository (mainly DSP and FPGA images) > although not a huge number: > > 15:58 ajb@sloy/x86_64 [work.git] >time git log --pretty=oneline -- xxx > xxx/xxxxxx/*.out ./xxx/xxx/*.out ./xxx/xxxxxxx/*.out | wc -l > 234 > > real 0m0.590s > user 0m0.552s > sys 0m0.040s log is streaming, and is not a good measure: it doesn't even walk the entire commit graph. How big are these files? > How can I tell if streaming is kicking in or now? I use callgrind (and kcachegrind to visualize). Can you post callgrind output? It will be helpful in figuring out where exactly git is spending time. ``` ## Thomas Rast, 2013-05-30 15:33 Subject: Re: Poor performance of git describe in big repos Message-ID: <87ehcoeb3t.fsf@linux-k42r.v.cablecom.net> URL: https://gitlist.dev/e/87ehcoeb3t.fsf%40linux-k42r.v.cablecom.net In-Reply-To: ``` Alex Bennée writes: > 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 > 33.62% git libz.so.1.2.3.4 [.] inflate_fast > 10.39% git libz.so.1.2.3.4 [.] adler32 > 2.03% git [kernel.kallsyms] [k] clear_page_c Do you have any large blobs in the repo that are referenced directly by a tag? Because this just so happens to exactly reproduce your symptoms: # in a random git.git $ time git describe --debug [...] real 0m0.390s user 0m0.037s sys 0m0.011s $ git tag big1 $(dd if=/dev/urandom bs=1M count=512 | git hash-object -w --stdin) 512+0 records in 512+0 records out 536870912 bytes (537 MB) copied, 45.5088 s, 11.8 MB/s $ time git describe --debug [...] real 0m1.875s user 0m1.738s sys 0m0.129s $ git tag big2 $(dd if=/dev/urandom bs=1M count=512 | git hash-object -w --stdin) 512+0 records in 512+0 records out 536870912 bytes (537 MB) copied, 44.972 s, 11.9 MB/s $ time git describe --debugsuche zur Beschreibung von HEAD [...] real 0m3.620s user 0m3.357s sys 0m0.248s (I actually ran the git-describe invocations more than once to ensure that they are again cache-hot.) git-describe should probably be fixed to avoid loading blobs, though I'm not sure off hand if we have any infrastructure to infer the type of a loose object without inflating it. (This could probably be added by inflating only the first block.) We do have this for packed objects, so at least for packed repos there's a speedup to be had. -- Thomas Rast trast@{inf,student}.ethz.ch ``` ## Alex Bennée, 2013-05-30 16:01 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NOjVhb%2B3Cab7uQE8K3VE0Q2GhqR3FE%3DWzJZvSn8Djt6tw%40mail.gmail.com In-Reply-To: <87ehcoeb3t.fsf@linux-k42r.v.cablecom.net> ``` On 30 May 2013 16:33, Thomas Rast wrote: > Alex Bennée writes: > >> 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 >> 33.62% git libz.so.1.2.3.4 [.] inflate_fast >> 10.39% git libz.so.1.2.3.4 [.] adler32 >> 2.03% git [kernel.kallsyms] [k] clear_page_c > > Do you have any large blobs in the repo that are referenced directly by > a tag? Most probably. I've certainly done a bunch of releases (which are tagged) were the last thing that was updated was an FPGA image. > Because this just so happens to exactly reproduce your symptoms: > > # in a random git.git > $ time git describe --debug > [...] > real 0m0.390s > user 0m0.037s > sys 0m0.011s > $ git tag big1 $(dd if=/dev/urandom bs=1M count=512 | git hash-object -w --stdin) > 512+0 records in > 512+0 records out > 536870912 bytes (537 MB) copied, 45.5088 s, 11.8 MB/s > $ time git describe --debug > [...] > real 0m1.875s > user 0m1.738s > sys 0m0.129s > $ git tag big2 $(dd if=/dev/urandom bs=1M count=512 | git hash-object -w --stdin) > 512+0 records in > 512+0 records out > 536870912 bytes (537 MB) copied, 44.972 s, 11.9 MB/s > $ time git describe --debugsuche zur Beschreibung von HEAD > [...] > real 0m3.620s > user 0m3.357s > sys 0m0.248s > > (I actually ran the git-describe invocations more than once to ensure > that they are again cache-hot.) That looks pretty promising as a replication. > git-describe should probably be fixed to avoid loading blobs, though I'm > not sure off hand if we have any infrastructure to infer the type of a > loose object without inflating it. (This could probably be added by > inflating only the first block.) We do have this for packed objects, so > at least for packed repos there's a speedup to be had. Will it be loading the blob for every commit it traverses or just ones that hit a tag? Why does it need to load the blob at all? Surely the commit tree state doesn't need to be walked down? > > -- > Thomas Rast > trast@{inf,student}.ethz.ch -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Thomas Rast, 2013-05-30 16:21 Subject: Re: Poor performance of git describe in big repos Message-ID: <87ip20bfq4.fsf@linux-k42r.v.cablecom.net> URL: https://gitlist.dev/e/87ip20bfq4.fsf%40linux-k42r.v.cablecom.net In-Reply-To: ``` Alex Bennée writes: > On 30 May 2013 16:33, Thomas Rast wrote: >> Alex Bennée writes: >> >>> 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 >>> 33.62% git libz.so.1.2.3.4 [.] inflate_fast >>> 10.39% git libz.so.1.2.3.4 [.] adler32 >>> 2.03% git [kernel.kallsyms] [k] clear_page_c >> >> Do you have any large blobs in the repo that are referenced directly by >> a tag? > > Most probably. I've certainly done a bunch of releases (which are tagged) were > the last thing that was updated was an FPGA image. [...] >> git-describe should probably be fixed to avoid loading blobs, though I'm >> not sure off hand if we have any infrastructure to infer the type of a >> loose object without inflating it. (This could probably be added by >> inflating only the first block.) We do have this for packed objects, so >> at least for packed repos there's a speedup to be had. > > Will it be loading the blob for every commit it traverses or just ones that hit > a tag? Why does it need to load the blob at all? Surely the commit > tree state doesn't > need to be walked down? No, my theory is that you tagged *the blobs*. Git supports this. git-describe needs to look at the commit (if any) obtained by peeling each tag (i.e. dereferencing tags until it reaches a non-tag). So to do that, it resolves the tag's referent and loads it. Usually this will be a commit, in which case it is marked as reached by the tag. As my example shows, it also resolves tags' referents if they refer to non-commits, in particular, it will decompress large blobs that are (directly) referenced by a tag. Note that while annotated tags provide the type information themselves, e.g. $ git cat-file tag junio-gpg-pub object fe113d3f96636710600c6b02d5fd421fa7e87dd6 type blob tag junio-gpg-pub [...] unannotated tags are simply refs, so it is not enough to just look at the tag objects' referent type. I had a brief look around sha1_file.c, in particular sha1_object_info, and it turns out we lack the "deflate only early part" logic as I suspected. So that'll have to be fixed first. After that I *think* it should automatically carry over into the tag readers. -- Thomas Rast trast@{inf,student}.ethz.ch ``` ## Thomas Rast, 2013-05-30 16:44 Subject: Re: Poor performance of git describe in big repos Message-ID: <87bo7sbeoc.fsf@linux-k42r.v.cablecom.net> URL: https://gitlist.dev/e/87bo7sbeoc.fsf%40linux-k42r.v.cablecom.net In-Reply-To: <87ip20bfq4.fsf@linux-k42r.v.cablecom.net> ``` Thomas Rast writes: > I had a brief look around sha1_file.c, in particular sha1_object_info, > and it turns out we lack the "deflate only early part" logic as I > suspected. So that'll have to be fixed first. After that I *think* it > should automatically carry over into the tag readers. Strike that, I'm wrong. sha1_object_info is fast even for these big loose objects. The culprit, according to some callgrind investigation, is lookup_commit_reference_gently() [for the unannotated case] or deref_tag() [annotated case] calling parse_object(). -- Thomas Rast trast@{inf,student}.ethz.ch ``` ## Antoine Pelisse, 2013-05-30 19:01 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CALWbr2xd4k_P6KUQOcRJotWj3%3DDfJNnhL4rsGSw0yE%2B53gdyWw%40mail.gmail.com In-Reply-To: <87bo7sbeoc.fsf@linux-k42r.v.cablecom.net> ``` > The culprit, according to some callgrind investigation, is > lookup_commit_reference_gently() [for the unannotated case] or > deref_tag() [annotated case] calling parse_object(). Using the scenario you described earlier, I think it ends-up spending most of its time in check_sha1_signature (both deref_tag and lookup_commit_reference_gently() go there) with 20% inflating, 80% in SHA1_Update(). Not much we can do about that, can we ? ``` ## John Keeping, 2013-05-30 19:30 Subject: Re: Poor performance of git describe in big repos Message-ID: <20130530193046.GG17475@serenity.lan> URL: https://gitlist.dev/e/20130530193046.GG17475%40serenity.lan In-Reply-To: <87ip20bfq4.fsf@linux-k42r.v.cablecom.net> ``` On Thu, May 30, 2013 at 06:21:55PM +0200, Thomas Rast wrote: > Alex Bennée writes: > > > On 30 May 2013 16:33, Thomas Rast wrote: > >> Alex Bennée writes: > >> > >>> 41.58% git libcrypto.so.1.0.0 [.] sha1_block_data_order_ssse3 > >>> 33.62% git libz.so.1.2.3.4 [.] inflate_fast > >>> 10.39% git libz.so.1.2.3.4 [.] adler32 > >>> 2.03% git [kernel.kallsyms] [k] clear_page_c > >> > >> Do you have any large blobs in the repo that are referenced directly by > >> a tag? > > > > Most probably. I've certainly done a bunch of releases (which are tagged) were > > the last thing that was updated was an FPGA image. > [...] > >> git-describe should probably be fixed to avoid loading blobs, though I'm > >> not sure off hand if we have any infrastructure to infer the type of a > >> loose object without inflating it. (This could probably be added by > >> inflating only the first block.) We do have this for packed objects, so > >> at least for packed repos there's a speedup to be had. > > > > Will it be loading the blob for every commit it traverses or just ones that hit > > a tag? Why does it need to load the blob at all? Surely the commit > > tree state doesn't > > need to be walked down? > > No, my theory is that you tagged *the blobs*. Git supports this. You can see if that is the case by doing something like this: eval $(git for-each-ref --shell --format ' test $(git cat-file -t %(objectname)^{}) = commit || echo %(refname);') That will print out the name of any ref that doesn't point at a commit. ``` ## Alex Bennée, 2013-05-31 08:14 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NOEuxOVy7LFp_XRa_08G-Mj0x7q%2BRiR%3Du71-iyfOXpHow%40mail.gmail.com In-Reply-To: <20130530193046.GG17475@serenity.lan> ``` On 30 May 2013 20:30, John Keeping wrote: > On Thu, May 30, 2013 at 06:21:55PM +0200, Thomas Rast wrote: >> Alex Bennée writes: >> >> > On 30 May 2013 16:33, Thomas Rast wrote: >> >> Alex Bennée writes: > >> > Will it be loading the blob for every commit it traverses or just ones that hit >> > a tag? Why does it need to load the blob at all? Surely the commit >> > tree state doesn't >> > need to be walked down? >> >> No, my theory is that you tagged *the blobs*. Git supports this. Wait is this the difference between annotated and non-annotated tags? I thought a non-annotated just acted like references to a particular tree state? > > You can see if that is the case by doing something like this: > > eval $(git for-each-ref --shell --format ' > test $(git cat-file -t %(objectname)^{}) = commit || > echo %(refname);') > > That will print out the name of any ref that doesn't point at a > commit. Hmm that didn't seem to work. But looking at the output by hand I certainly have a mix of tags that are commits vs tags: 09:08 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" | grep "commit" | wc -l 1345 09:12 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" | grep -v "commit" | wc -l 66 Unfortunately I can't just delete those tags as they do refer to known releases which we obviously care about. If I delete the tags on my local repo and test for a speed increase can I re-create them as annotated tag objects? -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Thomas Rast, 2013-05-31 08:24 Subject: Re: Poor performance of git describe in big repos Message-ID: <87obbr5zg3.fsf@linux-k42r.v.cablecom.net> URL: https://gitlist.dev/e/87obbr5zg3.fsf%40linux-k42r.v.cablecom.net In-Reply-To: ``` Alex Bennée writes: > On 30 May 2013 20:30, John Keeping wrote: >> On Thu, May 30, 2013 at 06:21:55PM +0200, Thomas Rast wrote: >>> Alex Bennée writes: >>> >>> > On 30 May 2013 16:33, Thomas Rast wrote: >>> >> Alex Bennée writes: >> >>> > Will it be loading the blob for every commit it traverses or just ones that hit >>> > a tag? Why does it need to load the blob at all? Surely the commit >>> > tree state doesn't >>> > need to be walked down? >>> >>> No, my theory is that you tagged *the blobs*. Git supports this. > > Wait is this the difference between annotated and non-annotated tags? > I thought a non-annotated just acted like references to a particular > tree state? A tag is just a ref. It can point at anything, in particular also a blob (= some file *contents*). An annotated tag is just a tag pointing at a "tag object". A tag object contains tagger name/email/date, a reference to an object, and a tag message. The slowness I found relates to having tags that point at blobs directly (unannotated). >> You can see if that is the case by doing something like this: >> >> eval $(git for-each-ref --shell --format ' >> test $(git cat-file -t %(objectname)^{}) = commit || >> echo %(refname);') >> >> That will print out the name of any ref that doesn't point at a >> commit. > > Hmm that didn't seem to work. But looking at the output by hand I > certainly have a mix of tags that are commits vs tags: > > > 09:08 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" > | grep "commit" | wc -l > 1345 > 09:12 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" > | grep -v "commit" | wc -l > 66 > > Unfortunately I can't just delete those tags as they do refer to known > releases which we obviously care about. If I delete the tags on my > local repo and test for a speed increase can I re-create them as > annotated tag objects? I would be more interested in this: git for-each-ref | grep ' blob' and (git for-each-ref | grep ' blob' | cut -d\ -f1 | xargs -n1 git cat-file blob) | wc -c The first tells you if you have any refs pointing at blobs. The second computes their total unpacked size. My theory is that the second yields some large number (hundreds of megabytes at least). It would be nice if you checked, because if there turn out to be big blobs, we have all the pieces and just need to assemble the best solution. Otherwise, there's something else going on and the problem remains open. -- Thomas Rast trast@{inf,student}.ethz.ch ``` ## John Keeping, 2013-05-31 08:32 Subject: Re: Poor performance of git describe in big repos Message-ID: <20130531083252.GA1072@serenity.lan> URL: https://gitlist.dev/e/20130531083252.GA1072%40serenity.lan In-Reply-To: ``` On Fri, May 31, 2013 at 09:14:49AM +0100, Alex Bennée wrote: > On 30 May 2013 20:30, John Keeping wrote: > > On Thu, May 30, 2013 at 06:21:55PM +0200, Thomas Rast wrote: > >> Alex Bennée writes: > >> > >> > On 30 May 2013 16:33, Thomas Rast wrote: > >> >> Alex Bennée writes: > > > >> > Will it be loading the blob for every commit it traverses or just ones that hit > >> > a tag? Why does it need to load the blob at all? Surely the commit > >> > tree state doesn't > >> > need to be walked down? > >> > >> No, my theory is that you tagged *the blobs*. Git supports this. > > Wait is this the difference between annotated and non-annotated tags? > I thought a non-annotated just acted like references to a particular > tree state? No, this is something slightly different. In Git there are four types of object: tag, commit, tree and blob. When you have a heavyweight tag, the tag reference points at a tag object (which in turn points at another object). With a lightweight tag, the tag reference typically points at a commit object. However, there is no restriction that says that a tag object must point to a commit or that a lightweight tag must point at a commit - it is equally possible to point directly at a tree or a blob (although a lot less common). Thomas is suggesting that you might have a tag that does not point at a commit but instead points to a blob object. > > You can see if that is the case by doing something like this: > > > > eval $(git for-each-ref --shell --format ' > > test $(git cat-file -t %(objectname)^{}) = commit || > > echo %(refname);') > > > > That will print out the name of any ref that doesn't point at a > > commit. > > Hmm that didn't seem to work. You mean there was no output? In that case it's likely that all your references do indeed point at commits. > But looking at the output by hand I > certainly have a mix of tags that are commits vs tags: > > > 09:08 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" > | grep "commit" | wc -l > 1345 > 09:12 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" > | grep -v "commit" | wc -l > 66 This means that you have 1345 lightweight tags and 66 heavyweight tags, assuming that all of the lines that don't say "commit" do say "tag". By the way, I don't remember if you said which version of Git you're using. If it's an older version then it's possible that something has changed. ``` ## Alex Bennée, 2013-05-31 08:40 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NOdg5TvjzEMrXaPgogU5z5W6kywZhD-82eTUmvE9Hp%3DLw%40mail.gmail.com In-Reply-To: <87obbr5zg3.fsf@linux-k42r.v.cablecom.net> ``` On 31 May 2013 09:24, Thomas Rast wrote: > Alex Bennée writes: >> On 30 May 2013 20:30, John Keeping wrote: >>> On Thu, May 30, 2013 at 06:21:55PM +0200, Thomas Rast wrote: >>>> Alex Bennée writes: >>>> > On 30 May 2013 16:33, Thomas Rast wrote: > >>>> No, my theory is that you tagged *the blobs*. Git supports this. >> >> Wait is this the difference between annotated and non-annotated tags? >> I thought a non-annotated just acted like references to a particular >> tree state? > > A tag is just a ref. It can point at anything, in particular also a > blob (= some file *contents*). > > An annotated tag is just a tag pointing at a "tag object". A tag object > contains tagger name/email/date, a reference to an object, and a tag > message. > > The slowness I found relates to having tags that point at blobs directly > (unannotated). I think you are right. I was brave (well I assumed the tags would come back from the upstream repo) and ran: git for-each-ref | grep "refs/tags" | grep "commit" | cut -d '/' -f 3 | xargs git tag -d And boom: 09:19 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771 real 0m0.009s user 0m0.008s sys 0m0.000s Which is much better performance. So it does look like unannotated tags pointing at binary blobs is the failure case. > > I would be more interested in this: > > git for-each-ref | grep ' blob' Hmmm that gives nothing. All the refs are either tag or commit > and > > (git for-each-ref | grep ' blob' | cut -d\ -f1 | xargs -n1 git >cat-file blob) | wc -c However I have some big commits it seems: 09:37 ajb@sloy/x86_64 [work.git] >(git for-each-ref | grep ' commit' | cut -d\ -f1 | xargs -n1 git cat-file commit) | wc -c 1147231984 > > The first tells you if you have any refs pointing at blobs. The second > computes their total unpacked size. My theory is that the second yields > some large number (hundreds of megabytes at least). > > It would be nice if you checked, because if there turn out to be big > blobs, we have all the pieces and just need to assemble the best > solution. Otherwise, there's something else going on and the problem > remains open. If you want any other numbers I'm only too happy to help. Sorry I can't share the repo though... -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Thomas Rast, 2013-05-31 08:46 Subject: Re: Poor performance of git describe in big repos Message-ID: <87y5av4jvj.fsf@linux-k42r.v.cablecom.net> URL: https://gitlist.dev/e/87y5av4jvj.fsf%40linux-k42r.v.cablecom.net In-Reply-To: ``` Alex Bennée writes: > I think you are right. I was brave (well I assumed the tags would come > back from the upstream repo) and ran: > > git for-each-ref | grep "refs/tags" | grep "commit" | cut -d '/' -f 3 > | xargs git tag -d So that deleted all unannotated tags pointing at commits, and then it was fast. Curious. > However I have some big commits it seems: > > 09:37 ajb@sloy/x86_64 [work.git] >(git for-each-ref | grep ' commit' | > cut -d\ -f1 | xargs -n1 git cat-file commit) | wc -c > 1147231984 How many unique entries are there in that list, i.e., what does git for-each-ref | grep ' commit' | cut -d\ -f1 | sort -u | wc -l say? Perhaps you can also find the biggest commit, e.g. like so: git for-each-ref | grep ' commit' | cut -d\ -f1 | while read sha; do git cat-file commit $sha | wc -c; done | sort -n However, if that turns out to be the culprit, it's not fixable currently[1]. Having commits with insanely long messages is just, well, insane. [1] unless we do a major rework of the loading infrastructure, so that we can teach it to load only the beginning of a commit as long as we are only interested in parents and such -- Thomas Rast trast@{inf,student}.ethz.ch ``` ## Alex Bennée, 2013-05-31 08:49 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NNgVPukJchskVv9oL7-9p%2BtxC0g_SXfHne-mwF327Q_3Q%40mail.gmail.com In-Reply-To: <20130531083252.GA1072@serenity.lan> ``` On 31 May 2013 09:32, John Keeping wrote: > On Fri, May 31, 2013 at 09:14:49AM +0100, Alex Bennée wrote: >> On 30 May 2013 20:30, John Keeping wrote: >> > On Thu, May 30, 2013 at 06:21:55PM +0200, Thomas Rast wrote: >> >> Alex Bennée writes: >> >> >> >> > On 30 May 2013 16:33, Thomas Rast wrote: >> >> >> Alex Bennée writes: >> > >> >> > Will it be loading the blob for every commit it traverses or just ones that hit >> >> > a tag? Why does it need to load the blob at all? Surely the commit >> >> > tree state doesn't >> >> > need to be walked down? >> >> >> >> No, my theory is that you tagged *the blobs*. Git supports this. >> >> Wait is this the difference between annotated and non-annotated tags? >> I thought a non-annotated just acted like references to a particular >> tree state? > > No, this is something slightly different. In Git there are four types > of object: tag, commit, tree and blob. When you have a heavyweight tag, > the tag reference points at a tag object (which in turn points at > another object). With a lightweight tag, the tag reference typically > points at a commit object. I think this is the case in my repo. > However, there is no restriction that says that a tag object must point > to a commit or that a lightweight tag must point at a commit - it is > equally possible to point directly at a tree or a blob (although a lot > less common). > > Thomas is suggesting that you might have a tag that does not point at a > commit but instead points to a blob object. It's looking like I just have some very heavy commits. One data point I probably should have mentioned at the beginning is this was a converted CVS repo and I'm wondering if some of the artifacts that introduced has contributed to this. >> > You can see if that is the case by doing something like this: >> > >> > eval $(git for-each-ref --shell --format ' >> > test $(git cat-file -t %(objectname)^{}) = commit || >> > echo %(refname);') >> > >> > That will print out the name of any ref that doesn't point at a >> > commit. >> >> Hmm that didn't seem to work. > > You mean there was no output? In that case it's likely that all your > references do indeed point at commits. Correct. > >> But looking at the output by hand I >> certainly have a mix of tags that are commits vs tags: >> >> >> 09:08 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" >> | grep "commit" | wc -l >> 1345 >> 09:12 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep "refs/tags" >> | grep -v "commit" | wc -l >> 66 > > This means that you have 1345 lightweight tags and 66 heavyweight tags, > assuming that all of the lines that don't say "commit" do say "tag". Yep all commits and tags, nothing else > By the way, I don't remember if you said which version of Git you're > using. If it's an older version then it's possible that something has > changed. I'm running the GIT stable PPA: 09:38 ajb@sloy/x86_64 [work.git] >git --version git version 1.8.3 Although I have also tested with the latest git.git maint. I'm happy to try master if it's likely to have changed. -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## John Keeping, 2013-05-31 08:59 Subject: Re: Poor performance of git describe in big repos Message-ID: <20130531085959.GB1072@serenity.lan> URL: https://gitlist.dev/e/20130531085959.GB1072%40serenity.lan In-Reply-To: ``` On Fri, May 31, 2013 at 09:49:57AM +0100, Alex Bennée wrote: > On 31 May 2013 09:32, John Keeping wrote: > > Thomas is suggesting that you might have a tag that does not point at a > > commit but instead points to a blob object. > > It's looking like I just have some very heavy commits. One data point > I probably should have mentioned at the beginning is this was a > converted CVS repo and I'm wondering if some of the artifacts that > introduced has contributed to this. You can try another for-each-ref invocation to see if that's the case: eval $(git for-each-ref --format 'printf "%s %s\n" \ $(git cat-file -s %(objectname)) %(refname);') | sort -n That will print the size of each object followed by the ref that points to it, sorted by size. > I'm running the GIT stable PPA: > > 09:38 ajb@sloy/x86_64 [work.git] >git --version > git version 1.8.3 > > Although I have also tested with the latest git.git maint. I'm happy > to try master if it's likely to have changed. master's still very close to 1.8.3 at the moment, so I don't think that will make a difference. ``` ## Alex Bennée, 2013-05-31 09:57 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NN8cARpPTnsCfHt3kY6gTnhZ%3DVq55EzqxWBV_3ju-oczQ%40mail.gmail.com In-Reply-To: <87y5av4jvj.fsf@linux-k42r.v.cablecom.net> ``` On 31 May 2013 09:46, Thomas Rast wrote: > Alex Bennée writes: > >> I think you are right. I was brave (well I assumed the tags would come >> back from the upstream repo) and ran: >> >> git for-each-ref | grep "refs/tags" | grep "commit" | cut -d '/' -f 3 >> | xargs git tag -d > > So that deleted all unannotated tags pointing at commits, and then it > was fast. Curious. > >> However I have some big commits it seems: >> >> 09:37 ajb@sloy/x86_64 [work.git] >(git for-each-ref | grep ' commit' | >> cut -d\ -f1 | xargs -n1 git cat-file commit) | wc -c >> 1147231984 > > How many unique entries are there in that list, i.e., what does > > git for-each-ref | grep ' commit' | cut -d\ -f1 | sort -u | wc -l 09:49 ajb@sloy/x86_64 [work.git] >git for-each-ref | grep ' commit' | cut -d\ -f1 | sort -u | wc -l 1508 > say? Perhaps you can also find the biggest commit, e.g. like so: > > git for-each-ref | grep ' commit' | cut -d\ -f1 | > while read sha; do git cat-file commit $sha | wc -c; done | > sort -n Yeah there is a range from a few hundred bytes to a large number of 3M commits. I guess I need to identify which commits they are and remove the tags or convert them to annotated reference tags. > However, if that turns out to be the culprit, it's not fixable > currently[1]. Having commits with insanely long messages is just, well, > insane. > > > [1] unless we do a major rework of the loading infrastructure, so that > we can teach it to load only the beginning of a commit as long as we are > only interested in parents and such I'll do a bit of scripting to dig into the nature of these uber-commits and try and work out how they cam about. I suspect they are simply start of branch states in our broken and disparate history. I'll get back to you once I've dug a little deeper. > > -- > Thomas Rast > trast@{inf,student}.ethz.ch -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Thomas Rast, 2013-05-31 10:27 Subject: Re: Poor performance of git describe in big repos Message-ID: <87txlj30n4.fsf@linux-k42r.v.cablecom.net> URL: https://gitlist.dev/e/87txlj30n4.fsf%40linux-k42r.v.cablecom.net In-Reply-To: <87y5av4jvj.fsf@linux-k42r.v.cablecom.net> ``` Thomas Rast writes: > However, if that turns out to be the culprit, it's not fixable > currently[1]. Having commits with insanely long messages is just, well, > insane. > > [1] unless we do a major rework of the loading infrastructure, so that > we can teach it to load only the beginning of a commit as long as we are > only interested in parents and such Actually, Peff, doesn't your commit parent/tree pointer caching give us this for free? -- Thomas Rast trast@{inf,student}.ethz.ch ``` ## Jeff King, 2013-05-31 16:17 Subject: Re: Poor performance of git describe in big repos Message-ID: <20130531161710.GB1365@sigill.intra.peff.net> URL: https://gitlist.dev/e/20130531161710.GB1365%40sigill.intra.peff.net In-Reply-To: <87txlj30n4.fsf@linux-k42r.v.cablecom.net> ``` On Fri, May 31, 2013 at 12:27:11PM +0200, Thomas Rast wrote: > Thomas Rast writes: > > > However, if that turns out to be the culprit, it's not fixable > > currently[1]. Having commits with insanely long messages is just, well, > > insane. > > > > [1] unless we do a major rework of the loading infrastructure, so that > > we can teach it to load only the beginning of a commit as long as we are > > only interested in parents and such > > Actually, Peff, doesn't your commit parent/tree pointer caching give us > this for free? It does. You can test it from the "jk/metapacks" branch at git://github.com/peff/git. After building, you'd need to do: $ git gc $ git metapack --all --commits in the target repository. You can check that it's working because "git rev-list --all --count" should be an order of magnitude faster. You may need to add "save_commit_buffer = 0" in any commands you are checking, though, as the optimization can only kick in if parse_commit does not want to save the buffer as a side effect. I also looked into trying to just read the beginning part of a commit[1], but it turned out not to be all that much of an improvement. -Peff [1] http://article.gmane.org/gmane.comp.version-control.git/212301 ``` ## Alex Bennée, 2013-06-03 08:02 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NNgcj_pPer2Tw4HvKkVib7N1ZFo7rZOrR9z8NMV1WHQsQ%40mail.gmail.com In-Reply-To: ``` On 31 May 2013 10:57, Alex Bennée wrote: > On 31 May 2013 09:46, Thomas Rast wrote: >> >> So that deleted all unannotated tags pointing at commits, and then it >> was fast. Curious. >> >> However, if that turns out to be the culprit, it's not fixable >> currently[1]. Having commits with insanely long messages is just, well, >> insane. >> >> >> [1] unless we do a major rework of the loading infrastructure, so that >> we can teach it to load only the beginning of a commit as long as we are >> only interested in parents and such > > I'll do a bit of scripting to dig into the nature of these > uber-commits and try and work out how they cam about. I suspect they > are simply start of branch states in our broken and disparate history. > > I'll get back to you once I've dug a little deeper. So I wrote a little script [1] which I ran to remove all tags that did not exist on any branches: git-tag-cleaner.py -d no-branch After a lot of churning: 17:26 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771 real 0m0.799s user 0m0.024s sys 0m0.052s So at least I can fix up my repo. All the big ones look at least as though they were weird cvs2svn creations that exist to represent the detached state of a strange CVS tag from the converted repository. However it does raise one question. Why is git attempting to parse a commit not on the DAG for the branch I'm attempting to describe? Anyway as I have a work around I'm going to do a slightly more conservative clean of the repo with my script and move on. [1] https://github.com/stsquad/git-tag-cleaner -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Alex Bennée, 2013-06-03 08:39 Subject: Re: Poor performance of git describe in big repos Message-ID: URL: https://gitlist.dev/e/CAJ-05NO2reGkboet1c2kYy0Y7xzkb9K45mTdCLq_AU7dp1OTNw%40mail.gmail.com In-Reply-To: <20130531161710.GB1365@sigill.intra.peff.net> ``` On 31 May 2013 17:17, Jeff King wrote: > On Fri, May 31, 2013 at 12:27:11PM +0200, Thomas Rast wrote: > >> Thomas Rast writes: >> >> > However, if that turns out to be the culprit, it's not fixable >> > currently[1]. Having commits with insanely long messages is just, well, >> > insane. >> > >> > [1] unless we do a major rework of the loading infrastructure, so that >> > we can teach it to load only the beginning of a commit as long as we are >> > only interested in parents and such >> >> Actually, Peff, doesn't your commit parent/tree pointer caching give us >> this for free? > > It does. You can test it from the "jk/metapacks" branch at > git://github.com/peff/git. After building, you'd need to do: > > $ git gc > $ git metapack --all --commits > > in the target repository. You can check that it's working because "git > rev-list --all --count" should be an order of magnitude faster. You may > need to add "save_commit_buffer = 0" in any commands you are checking, > though, as the optimization can only kick in if parse_commit does not > want to save the buffer as a side effect. Is this a command line argument? The tools don't seem to think so. Anyway it seems to make a marginal difference to my case: 09:08 ajb@sloy/x86_64 [work.git] >time git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771 real 0m14.105s user 0m12.409s sys 0m1.660s 09:11 ajb@sloy/x86_64 [work.git] >git gc Counting objects: 399436, done. Delta compression using up to 4 threads. Compressing objects: 100% (110874/110874), done. Writing objects: 100% (399436/399436), done. Total 399436 (delta 281538), reused 398357 (delta 280493) Checking connectivity: 399436, done. 09:12 ajb@sloy/x86_64 [work.git] >git metapack --all --commits 09:13 ajb@sloy/x86_64 [work.git] >time git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771 real 0m12.781s user 0m11.669s sys 0m1.080s 09:32 ajb@sloy/x86_64 [work.git] >time git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771 real 0m12.768s user 0m11.817s sys 0m0.908s 09:33 ajb@sloy/x86_64 [work.git] >time git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771 real 0m12.642s user 0m11.705s sys 0m0.904s > > I also looked into trying to just read the beginning part of a commit[1], > but it turned out not to be all that much of an improvement. > > -Peff > > [1] http://article.gmane.org/gmane.comp.version-control.git/212301 -- Alex, homepage: http://www.bennee.com/~alex/ ``` ## Jeff King, 2013-06-03 14:49 Subject: Re: Poor performance of git describe in big repos Message-ID: <20130603144907.GA5938@sigill.intra.peff.net> URL: https://gitlist.dev/e/20130603144907.GA5938%40sigill.intra.peff.net In-Reply-To: ``` On Mon, Jun 03, 2013 at 09:39:21AM +0100, Alex Bennée wrote: > > in the target repository. You can check that it's working because "git > > rev-list --all --count" should be an order of magnitude faster. You may > > need to add "save_commit_buffer = 0" in any commands you are checking, > > though, as the optimization can only kick in if parse_commit does not > > want to save the buffer as a side effect. > > Is this a command line argument? The tools don't seem to think so. If you mean the "save_commit_buffer = 0", no; I mean you would have to insert it somewhere in builtin/$CMD.c, and then recompile. However, git-describe already has it, so it should work. > Anyway it seems to make a marginal difference to my case: I get much better results: $ cd linux-2.6 $ time git --no-pager describe --long --tags HEAD~800 v3.5-6956-gaa0b3b2 real 0m0.261s user 0m0.248s sys 0m0.012s $ git metapack --commits --all $ time git --no-pager describe --long --tags HEAD~800 v3.5-6956-gaa0b3b2 real 0m0.057s user 0m0.032s sys 0m0.024s which implies that your time is being spent elsewhere. That topic wouldn't avoid inflating tag objects from disk. Do you have really big tag objects (or unannotated tags pointing to blobs)? What does: git for-each-ref --format='%(object)' refs/tags | git cat-file --batch-check | sort -k 3nr | head say? -Peff ``` ## Junio C Hamano, 2013-06-03 16:32 Subject: Re: Poor performance of git describe in big repos Message-ID: <7vfvwzi29f.fsf@alter.siamese.dyndns.org> URL: https://gitlist.dev/e/7vfvwzi29f.fsf%40alter.siamese.dyndns.org In-Reply-To: ``` Alex Bennée writes: > Why is git attempting to parse a commit not on the DAG for the branch > I'm attempting to describe? I think that is because you need to parse the objects at the tip of refs to see if they are on the DAG in the first place. If there weren't any annotated tag, conceivably you could do without parsing these objects. You would: - First read the refs without parsing anything to learn the object name of the tips of refs; - Traverse the DAG, starting from the commit and notice when you see commits that are at the tips of refs you learned in the first step, arranging to stop when you found the "closest" tip. But with annotated tags (and "git describe" is designed to be primarily used with them; you would need "--tags" option to make it notice unannotated tags), the object name you see sitting at the tip will never appear during the DAG traversal. You will only see commits from the latter, so you would need to parse the tips to learn what commits they refer to. And of course, "then parse only annotated tags, without parsing commits" would not work, because you wouldn't know what the object is without looking at it ;-) ``` ## Junio C Hamano, 2013-06-03 17:48 Subject: Re: Poor performance of git describe in big repos Message-ID: <7v1u8jgk55.fsf@alter.siamese.dyndns.org> URL: https://gitlist.dev/e/7v1u8jgk55.fsf%40alter.siamese.dyndns.org In-Reply-To: <7vfvwzi29f.fsf@alter.siamese.dyndns.org> ``` Junio C Hamano writes: > Alex Bennée writes: > >> Why is git attempting to parse a commit not on the DAG for the branch >> I'm attempting to describe? > > I think that is because you need to parse the objects at the tip of > refs to see if they are on the DAG in the first place. > > If there weren't any annotated tag, conceivably you could do without > parsing these objects. You would: > > - First read the refs without parsing anything to learn the object > name of the tips of refs; > > - Traverse the DAG, starting from the commit and notice when you > see commits that are at the tips of refs you learned in the first > step, arranging to stop when you found the "closest" tip. > > But with annotated tags (and "git describe" is designed to be > primarily used with them; you would need "--tags" option to make it > notice unannotated tags), the object name you see sitting at the tip > will never appear during the DAG traversal. You will only see > commits from the latter, so you would need to parse the tips to > learn what commits they refer to. > > And of course, "then parse only annotated tags, without parsing > commits" would not work, because you wouldn't know what the object > is without looking at it ;-) Having said all that, with changes by Peff and Michael Haggerty around f85354b5c7b8 (pack_one_ref(): use function peel_entry(), 2013-04-22), recent Git does not "parse" as many refs as it used to, only to figure out what commit an annotated tag points at when your refs are packed, so we may be a lot closer to the optimum than I hinted by the above description. ```