From: Mike Hommey <email@example.com> To: Christian Couder <firstname.lastname@example.org> Cc: Constantine <email@example.com>, git <firstname.lastname@example.org> Subject: Re: git-clone causes out of memory Date: Fri, 13 Oct 2017 19:37:22 +0900 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <CAP8UFD1KuBdUCo=x_q4__s1kW15CWMH1jJkKzXqmf3=T3jcrng@mail.gmail.com> On Fri, Oct 13, 2017 at 12:26:46PM +0200, Christian Couder wrote: > On Fri, Oct 13, 2017 at 12:06 PM, Mike Hommey <firstname.lastname@example.org> wrote: > > On Fri, Oct 13, 2017 at 12:51:58PM +0300, Constantine wrote: > >> There's a gitbomb on github. It is undoubtedly creative and funny, but since > >> this is a bug in git, I thought it'd be nice to report. The command: > >> > >> $ git clone https://github.com/x0rz/ShadowBrokersFiles > > > > What fills memory is actually the checkout part of the command. git > > clone -n doesn't fail. > > > > Credit should go where it's due: https://kate.io/blog/git-bomb/ > > (with the bonus that it comes with explanations) > > Yeah, there is a thread on Hacker News about this too: > > https://news.ycombinator.com/item?id=15457076 > > The original repo on GitHub is: > > https://github.com/Katee/git-bomb.git > > After cloning it with -n, there is the following "funny" situation: > > $ time git rev-list HEAD > 7af99c9e7d4768fa681f4fe4ff61259794cf719b > 18ed56cbc5012117e24a603e7c072cf65d36d469 > 45546f17e5801791d4bc5968b91253a2f4b0db72 > > real 0m0.004s > user 0m0.000s > sys 0m0.004s > $ time git rev-list HEAD -- d0/d0/d0/d0/d0/d0/d0/d0/d0/d0/f0 > > real 0m0.004s > user 0m0.000s > sys 0m0.000s > $ time git rev-list HEAD -- d0/d0/d0/d0/d0/d0/d0/d0/d0/d0 > > real 0m0.004s > user 0m0.000s > sys 0m0.000s > $ time git rev-list HEAD -- d0/d0/d0/d0/d0/d0/d0/d0/ > 45546f17e5801791d4bc5968b91253a2f4b0db72 > > real 0m0.005s > user 0m0.008s > sys 0m0.000s > $ time git rev-list HEAD -- d0/d0/d0/d0/d0/ > 45546f17e5801791d4bc5968b91253a2f4b0db72 > > real 0m0.203s > user 0m0.112s > sys 0m0.088s > $ time git rev-list HEAD -- d0/d0/d0/d0/ > 45546f17e5801791d4bc5968b91253a2f4b0db72 > > real 0m1.305s > user 0m0.720s > sys 0m0.580s > $ time git rev-list HEAD -- d0/d0/d0/ > 45546f17e5801791d4bc5968b91253a2f4b0db72 > > real 0m12.135s > user 0m6.700s > sys 0m5.412s > > So `git rev-list` becomes exponentially more expensive when you run it > on a shorter directory path, though it is fast if you run it without a > path. That's because there are 10^7 files under d0/d0/d0, 10^6 under d0/d0/d0/d0/, 10^5 under d0/d0/d0/d0/d0/ etc. So really, this is all about things being slower when there's a crazy number of files. Picture me surprised. What makes it kind of special is that the repository contains a lot of paths/files, but very few objects, because it's duplicating everything. All the 10^10 blobs have the same content, all the 10^9 trees that point to them have the same content, all the 10^8 trees that point to those trees have the same content, etc. If git wasn't effectively deduplicating identical content, the repository would be multiple gigabytes large. Mike
next prev parent reply other threads:[~2017-10-13 10:37 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-13 9:51 Constantine 2017-10-13 10:06 ` Mike Hommey 2017-10-13 10:26 ` Christian Couder 2017-10-13 10:37 ` Mike Hommey [this message] 2017-10-13 10:44 ` Christian Couder 2017-10-13 12:04 ` Junio C Hamano 2017-10-13 12:12 ` Constantine 2017-10-13 12:44 ` Jeff King 2017-10-13 13:15 ` Derrick Stolee 2017-10-13 13:39 ` Derrick Stolee 2017-10-13 13:50 ` Jeff King 2017-10-13 13:55 ` Derrick Stolee 2017-10-13 13:56 ` Jeff King 2017-10-13 14:10 ` Jeff King 2017-10-13 14:20 ` Jeff King 2017-10-13 14:25 ` Derrick Stolee 2017-10-13 14:26 ` Jeff King 2017-10-13 14:30 ` Derrick Stolee 2017-10-13 15:27 ` [PATCH] revision: quit pruning diff more quickly when possible Jeff King 2017-10-13 15:37 ` Derrick Stolee 2017-10-13 15:44 ` Jeff King 2017-10-14 2:43 ` Junio C Hamano 2017-10-13 12:35 ` git-clone causes out of memory Jeff King
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