Some timings using bzr

[Robert Collins]

On Fri, 2008-07-11 at 08:21 +0200, David Ingamells wrote:

> A simple copy of the repository (including the .bzr directory) from
> NFS to a local disk on desk01 takes 3.1 seconds and NFS to NFS takes
> 84 seconds at a low-load time of day. Clearly there is significant
> room for improvement in bzr when you compare the closest bzr
> equivalents to this copy  (36 and 187 seconds). From an admittedly
> very naive perspective, the branch bzr makes is only a copy of the
> repos (when branch is used without options).

bzr verifies the data it copies; its much more than just a copy. That
said, we improve things every chance we get :).

> The time shown for each test is the best seen of the few runs I did.
> Especially with the NFS to NFS tests I saw huge variations (e.g. from
> 13 minutes to 38 minutes for one test). The tests show:


>      1. File:// is better than bzr:// when using a local destination.
>         Surprisingly bzr:// across the network was quicker than bzr://
>         used on the same machine.

Using bzr:// locally means you have twice the overhead - you have bzr
running twice and processing data twice. So I'd expect it to be slower.
When you have two machines each gets to share the load.

With regard to formats - we are continually looking at things we can
improve with regard to the disk formats we use. So 'old' really refers
to how much we have learnt since we made a specific format the default.
We have a pipeline of things we believe will bring better tradeoffs,
solve bugs, increase performance etc. I expect we'll continue to bring
these into experimental and development formats, and do regular drops to
'stable' formats that we then support and make default. We also add
features that don't actually change the underlying storage, but do
change how we use the data stored in the store; these require format
marker changes to prevent incorrect behaviour by older clients.

For instance, the pack-0.92 format is very robust, but it is not as
compact on disk as we'd like, and we have some ideas about how to
improve this that are being experimented with now.

-Rob

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