Re: [PATCH] fetch, clone: add fetch.blobSizeLimit config

From: Alan Braithwaite <alan@braithwaite.dev>
Date: Mar 2, 2026, 21:36 UTC
Message-ID: <a3e064fe-9f0d-448f-b034-4a95dcd3fe97@app.fastmail.com>
In-Reply-To: <xmqq342i12ky.fsf@gitster.g>

Patrick, Peff, Junio — thanks for taking the time to look at this.

Patrick wrote:

> I'm not sure that we should make blob size limiting the
> default.

To clarify — this is a user-opt-in config, not a default. You would only get partial clone behavior if you explicitly set fetch.blobSizeLimit in your gitconfig.

Peff wrote:

> We actually can do blob:limit filters with bitmaps. See
> 84243da129 (pack-bitmap: implement BLOB_LIMIT filtering,
> 2020-02-14).

Good to know. I'm not positive, but my understanding is that this patch only touches client code, and the server sees an identical request to what `git clone --filter=blob:limit=1m` already sends today. If that's correct, anyone can already impose that cost — this patch just makes it easier to opt in.

> All that said, I'd be wary of turning on partial clones like
> this by default.

That's fair. I'm not attached to getting this merged — it was more exploratory to start a discussion.

Junio wrote:

> As to this extra variable, it can already be done with
> existing remote.*.partialCloneFilter, it seems, so I do not
> know why we want to add it.

I may not understand the config as well as you do, but my reading is that remote.*.partialCloneFilter requires a specific remote name and only takes effect on subsequent fetches from an already-registered promisor remote — not the initial clone. You would also need remote.origin.promisor=true set globally, which seems odd. If I'm understanding correctly, there is currently no way to say "all new clones should use a blob size filter" via config alone. But please correct me if I'm wrong.

Separately — is my understanding correct that partial clone with blob:limit works today without server-side changes, assuming uploadpack.allowFilter is enabled? If so, I'm happy to maintain this as a local client patch for my own workflow.

Thanks again, Alan

On Mon, Mar 2, 2026, at 10:57, Junio C Hamano wrote:

Show 19 quoted lines

> Patrick Steinhardt <ps@pks.im> writes:
>
>> I'm not sure that we should make blob size limiting the default. The
>> problem with specifying a limit is that this is comparatively expensive
>> to compute on the server side: we have to look up each blob so that we
>> can determine its size. Unfortunately, such requests cannot (currently)
>> be optimized via for example bitmaps, or any other cache that we have.
>> ...
>> Another question to consider: is it really sensible to set this setting
>> globally? It is very much dependent on the forge that you're connecting
>> to, as forges may not even allow object filters at all, or only a subset
>> of them.
>
> Both are good questions, but to affect "clone" you'd need either
> "git -c that.variable=setting clone" or have it in ~/.gitconfig no?
>
> As to this extra variable, it can already be done with existing
> remote.*.partialCloneFilter, it seems, so I do not know why we want
> to add it.