From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <gitster@pobox.com>
Subject: Re: Reverting an uncommitted revert
Date: Wed, 20 May 2009 23:16:17 -0700
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Cc: "Shawn O. Pearce" <spearce@spearce.org>,
	Wincent Colaiuta <win@wincent.com>, Jeff King <peff@peff.net>,
	Joshua Jensen <jjensen@workspacewhiz.com>, git@vger.kernel.org
To: Nicolas Pitre <nico@cam.org>
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In-Reply-To: <alpine.LFD.2.00.0905201406280.3906@xanadu.home> (Nicolas Pitre's message of "Wed\, 20 May 2009 14\:19\:09 -0400 \(EDT\)")
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Nicolas Pitre <nico@cam.org> writes:

>>  (1) When would you "auto" write-tree?  When you do "git add" or anything
>>      that adds new contents to the index?  Or immediately before you do
>>      something destructive like "git reset"?  Or perhaps both?
>
> Delaying any IO until it is clear that something is to be discarded is 
> the best approach performance wise.  So perhaps not on the first 'git 
> add' but certainly on the second one with an already cached path for 
> which new (different) content is going to replace previous content.

I hope that you are not forgetting that it costs cycles to determine "it
is clear that something is to be discarded".

The "diff-index --cached" optimization I did today may help, as it would
allow you to check with the last trash-log more cheaply, but it certainly
is not free.