Re: How git affects kernel.org performance

From: Shawn O. Pearce <spearce@spearce.org>
Date: Jan 7, 2007, 20:31 UTC
Message-ID: <20070107203120.GA4970@spearce.org>
In-Reply-To: <m3odpazxit.fsf@defiant.localdomain>

Krzysztof Halasa <khc@pm.waw.pl> wrote:

> Hmm... Perhaps it should be possible to push git updates as a pack
> file only? I mean, the pack file would stay packed = never individual
> files and never 256 directories?

Latest Git does this. If the server is later than 1.4.3.3 then the receive-pack process can actually store the pack file rather than unpacking it into loose objects. The downside is that it will copy any missing base objects onto the end of a thin pack to make it not-thin.

There's actually a limit that controls when to keep the pack and when not to (receive.unpackLimit). In 1.4.3.3 this defaulted to 5000 objects, which meant all but the largest pushes will be exploded into loose objects. In 1.5.0-rc0 that limit changed from 5000 to 100, though Nico did a lot of study and discovered that the optimum is likely 3. But that tends to create too many pack files so 100 was arbitrarily chosen.

So if the user pushes <100 objects to a 1.5.0-rc0 server we unpack
to loose; >= 100 we keep the pack file.  Perhaps this would help
kernel.org.

-- 
Shawn.