Re: [PATCH v2 1/2] read-cache: skip index SHA verification

From: Jeff King <peff@peff.net>
Date: Mar 27, 2017, 22:44 UTC
Message-ID: <20170327224408.2bzh5vfa6deni6fm@sigill.intra.peff.net>
In-Reply-To: <1490648979-49580-2-git-send-email-git@jeffhostetler.com>

On Mon, Mar 27, 2017 at 09:09:38PM +0000, git@jeffhostetler.com wrote:

Show 15 quoted lines

> From: Jeff Hostetler <jeffhost@microsoft.com>
> 
> Teach git to skip verification of the index SHA in read_index().
> 
> This is a performance optimization.  The index file SHA verification
> can be considered an ancient relic from the early days of git and only
> useful for detecting disk corruption.  For small repositories, this
> SHA calculation is not that significant, but for gigantic repositories
> this calculation adds significant time to every command.
> 
> I added a global "skip_verify_index" variable to control this and
> allow it to be tested.
> 
> I did not create a config setting for this because of chicken-n-egg
> problems with the loading the config and the index.

Hrm, there shouldn't be any dependency of the config on the index (and there are a handful of options which impact the index already). Did you try it and run into problems?

In general, I'd much rather see us either:

  1. Rip the code out entirely if it is not meant to be configurable,
     and cannot be triggered by the actual git binary.

or

  2. Make it configurable, even if most people wouldn't use it. And then
     have a test to exercise it using a git command (unlike the one-off
     test helper, which isn't run at all).

-Peff