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From: Junio C Hamano <junkio@cox.net>
Subject: Re: git-fetching from a big repository is slow
Date: Thu, 14 Dec 2006 12:41:38 -0800
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To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Sender: git-owner@vger.kernel.org

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> git-show-ref traverses every single _local_ tag when called. This is to 
> overcome the problem that tags can be packed now, so a simple file 
> existence check is not sufficient.

Is "traverses every single _local_ tag" a fact?  It might go
through every single _local_ (possibly stale) packed tag in
memory but it should not traverse $GIT_DIR/refs/tags.

If I recall correctly, show-ref (1) first checks the filesystem
"$GIT_DIR/$named_ref" and says Ok if found and valid; otherwise
(2) checks packed refs (reads $GIT_DIR/packed-refs if not
already).  So that would be at most one open (which may fail in
(1)) and one open+read (in (2)).  Unless we are talking about
fork+exec overhead, that "traverse" should be reasonably fast.

Where is the bottleneck?