Re: [RFC] Reporting index properties

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Oct 6, 2017, 03:13 UTC
Message-ID: <20171006031303.GB134987@aiede.mtv.corp.google.com>
In-Reply-To: <alpine.DEB.2.10.1710051625430.812@alexmv-linux>

Alex Vandiver wrote:

Show 7 quoted lines

> As part of gathering some automated performance statistics of git, it
> would be useful to be able to extract some vital properties of the
> index.  While `git update-index` has ways to _set_ the index version,
> and enable/disable various extensions, AFAICT there is no method by
> which one can ask for reporting about the current state of them --
> short of re-implementing all of the index-parsing logic external to
> Git, which is not terribly appealing.

Aside: git-update-index(1) says

	Version 4 is relatively young (first released in 1.8.0 in
	October 2012).

My first reaction is to wonder if it is time to introduce a config option to use index format version 4 by default, since after 5 years it is not relatively young any more.

My second reaction is to notice that the index.version configuration already exists. Probably git-update-index(1) ought to point to it.

JGit still doesn't support index format 4, so 4 is still not a good default for `index.version` for a user that hasn't explicitly configured it, but the moment JGit gains that support I think it will be. :)

> I hesitate to propose adding a flag to `git update-index` which reads
> but does no updating, as that seems to make a misnomer of the
> command.  But this also doesn't seem worthy of a new top-level command.

The existing scripting command that inspects the index is "git ls-files".

It doesn't go into this kind of low-level detail about the index format, though. In the same spirit, I don't think we have an existing command in this spirit for analyzing packfiles, either.

So I agree with Junio that this would be a good debugging aid to put in t/helper/ for now, and then once we've had experience with it we'd end up in a better position to come up with a stable, public-facing interface, if one is needed.

Thanks and hope that helps, Jonathan