Re: Fetching a lot of repos

From: Soni "They/Them" L. <fakedme@gmail.com>
Date: Jun 8, 2020, 16:03 UTC
Message-ID: <62cee46f-d37d-0e51-143e-b2e9c10f5b0f@gmail.com>
In-Reply-To: <20200607210344.GK6569@camp.crustytoothpaste.net>

On 2020-06-07 6:03 p.m., brian m. carlson wrote:

Show 62 quoted lines

> On 2020-06-07 at 20:04:03, Soni "They/Them" L. wrote:
> > -----
> > 
> > [soniex2@soniex-pc multigit]$ git fetch
> > https://soniex2.autistic.space/git-repos/ganarchy.git +HEAD:repo_a & git
> > fetch https://github.com/ganarchy/GAnarchy +HEAD:repo_b & git fetch
> > https://cybre.tech/SoniEx2/ganarchy +HEAD:repo_c & git fetch
> > https://soniex2.autistic.space/git-repos/abdl.git +HEAD:repo_d & git fetch
> > https://cybre.tech/SoniEx2/rust.hexchat.hexchat-plugin +HEAD:repo_e
> > [1] 2236
> > [2] 2237
> > [3] 2238
> > [4] 2239
> > remote: Enumerating objects: 87, done.
> > remote: Total 87 (delta 0), reused 0 (delta 0), pack-reused 87
> > Unpacking objects: 100% (87/87), 36.06 KiB | 225.00 KiB/s, done.
> > From https://github.com/ganarchy/GAnarchy
> >  * [new ref]                    -> repo_b
> > From https://cybre.tech/SoniEx2/ganarchy
> >  * [new ref]                    -> repo_c
> > warning: no common commits
> > remote: Counting objects: 113, done.
> > remote: Compressing objects: 100% (74/74), done.
> > remote: Total 113 (delta 48), reused 88 (delta 38)
> > Receiving objects: 100% (113/113), 30.07 KiB | 138.00 KiB/s, done.
> > Resolving deltas: 100% (48/48), done.
> > From https://cybre.tech/SoniEx2/rust.hexchat.hexchat-plugin
> >  * [new ref]                    -> repo_e
> > [2]   Done                    git fetch https://github.com/ganarchy/GAnarchy
> > +HEAD:repo_b
> > [3]-  Done                    git fetch https://cybre.tech/SoniEx2/ganarchy
> > +HEAD:repo_c
> > [soniex2@soniex-pc multigit]$ error: unable to write file
> > .git/objects/d2/5baa9c0a78b0007a34a569b774d983b905f0b5: No such file or
> > directory
> > error: unable to write file
> > .git/objects/ba/f9414a35a2f48ed1b22644fd4522272fb4bc66: No such file or
> > directory
> > error: unable to write sha1 filename
> > .git/objects/ba/f9414a35a2f48ed1b22644fd4522272fb4bc66
> > error: Unable to find baf9414a35a2f48ed1b22644fd4522272fb4bc66 under
> > https://soniex2.autistic.space/git-repos/abdl.git
> > Fetching objects: 12, done.
> > Cannot obtain needed blob baf9414a35a2f48ed1b22644fd4522272fb4bc66
> > while processing commit 3f9f66712aaa071bd3bb32c46e1e4dc1fed13378.
> > error: fetch failed.
> > Fetching objects: 78, done.
> > From https://soniex2.autistic.space/git-repos/ganarchy
> >  * [new ref]                    -> repo_a
> > 
> > -----
>
> So when Git needs to write a loose object, it will create the sharded
> directory if it doesn't exist.  If it removes all of the objects in that
> directory, it will remove the directory, which is likely what you're
> seeing here.
>
> In general, I wouldn't recommend fetching in parallel, but if you want
> to do it anyway, I'd suggest setting `receive.unpackLimit` to 1.  That
> will result in you keeping the packs you've fetched instead of exploding
> them into loose objects, which will help this case.  It may not help
> enough to solve the problem, though.

That didn't work either, unfortunately. It was worth a shot tho, thanks.

Show 28 quoted lines

>
> > So I figured, "okay this is a git gc issue", and started over (rm -rf .git,
> > git init) and turned off the GC (git config --local gc.auto 0, and that long
> > command to run 5 git fetch at the same time). At first, it seemed to work
> > fine, but then...
> > 
> > -----
> > 
> > $ git gc --aggressive
> > Enumerating objects: 365, done.
> > error: object file .git/objects/ba/f9414a35a2f48ed1b22644fd4522272fb4bc66 is
> > empty
> > Counting objects: 100% (365/365), done.
> > Delta compression using up to 4 threads
> > Compressing objects: 100% (357/357), done.
> > error: object file .git/objects/ba/f9414a35a2f48ed1b22644fd4522272fb4bc66 is
> > empty
> > fatal: loose object baf9414a35a2f48ed1b22644fd4522272fb4bc66 (stored in
> > .git/objects/ba/f9414a35a2f48ed1b22644fd4522272fb4bc66) is corrupt
> > fatal: failed to run repack
> > 
> > -----
>
> It looks like this particular object is corrupt.  If you fetch with
> packs this should go away, but you'll need to find which repo it's from,
> clone it (without receive.packLimit set), and replace it.  Then run git
> fsck to see if you have any more objects that are a problem.  Anything
> that says "dangling" can be ignored, but other issues can be a problem.

So I can do parallel fetches but I'd have to check that everything is good and re-fetch what got broken? That kinda defeats the purpose of parallel fetch. On the other hand, the repos with no shared commits don't seem to cause an issue, but the ones with shared commits do. However, I have no reliable way of telling which repos have shared commits, as one can merge unrelated branches.

Another idea I had was to make local clones using symlinks (IIRC there was a way to do that, but I can't remember how to do it), do parallel remote fetches into separate local repos, then do quick local fetches sequentially instead. It's probably the safest way to do it.

Relatedly, but not relevant for my use-case: Is it safe to assume that currently git breaks if multiple ppl push into the same repo at the same time, and they have not-yet-upstreamed shared commits, in particular if they're pushing to different branches?