RE: [External Mail]Re: Partial-clone cause big performance impact on server

[程洋 <chengyang@xiaomi.com>]

Sorry, I told you the wrong branch. It should be "android-t-preview-1"
git clone --filter=blob:none --no-local -b android-t-preview-1 grade-plugin

Can you try this one?

> > At first I also think it's some implementation bugs by jgit. However I
> > can also reproduce it on cgit. Here is the steps, I'm not sure if you
> > can reproduce too.
> >
> > 1. Clone a repository from AOSP to local machine:  `git clone
> >
> > "https://android.googlesource.com/platform/prebuilts/gradle-plugin"`
> > 2. try to clone from localhost using cgit server.
> >    `GIT_TRACE_PACKET=1 git clone --filter=blob:none -b master
> >    user@localhost:/home/user/repositories/gradle-plugin ` 3. During
> > checkout phase, it also takes 15 seconds before actual downloading.
>
> I don't see that at all. A few things on your reproduction:
>
>   - you have to tell the local server repo that filters are OK:
>
>       git -C gradle-plugin config uploadpack.allowfilter true
>
>   - your example goes over localhost ssh. Is your server configured to
>     allow passing the GIT_PROTOCOL environment variable? If not, you're
>     using the v0 protocol. In which case you'll have to set a config
>     option to allow clients to fetch objects that the server didn't
>     advertise.
>
>     If you do it with allowReachableSHA1InWant, like this:
>
>       git -C gradle-plugin config uploadpack.allowReachableSHA1InWant true
>
>     then there will be a short delay while it checks their
>     reachability. That check happens via an external rev-list. I think
>     it's not clever enough to use bitmaps, though it could. However, in
>     this example, the delay only seems to be around 800ms for me (and of
>     course we didn't generate bitmaps anyway, so that wouldn't matter).
>
>     If you instead do:
>
>       git -C gradle-plugin config uploadpack.allowAnySHA1InWant true
>
>     then that reachability check goes away.
>
>     But on modern servers, most of this should be moot anyway. A
>     well-configured server should support protocol v2, which defaults to
>     allowAnySHA1InWant.
>
>     If you use --no-local to disable local-clone optimizations, then you
>     can use --filter without having to go through ssh. That should use
>     protocol version 2, as a "real" server would.
>
> So all told, I think a more realistic reproduction is:
>
>   $ git clone https://android.googlesource.com/platform/prebuilts/gradle-
> plugin
>   $ git -C gradle-plugin config uploadpack.allowfilter true
>   $ git clone --filter=blob:none --no-local -b master grade-plugin foo
>
> which takes ~3s for me.
>
> I do think upload-pack spends more time than it needs in this case, as it's
> keen to call parse_object() on oids that the client asks for. Which means we'll
> open up those blobs and check their sha1s before sending them out, which
> isn't strictly necessary.
>
> All of this seems orthogonal to the original claim that "Counting objects" was
> taking a while, though. The delays here are all inside upload-pack, before it
> spawns pack-objects. And it's pack-objects that says "Counting objects".
>
> -Peff
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