From: Jeff King <peff@peff.net>
To: Phil Hord <phil.hord@gmail.com>
Cc: Git <git@vger.kernel.org>
Subject: Re: [PATCH] defer expensive load_ref_decorations until needed
Date: Wed, 22 Nov 2017 16:27:11 -0500 [thread overview]
Message-ID: <20171122212710.GB2854@sigill> (raw)
In-Reply-To: <20171121234336.10209-1-phil.hord@gmail.com>
On Tue, Nov 21, 2017 at 03:43:36PM -0800, Phil Hord wrote:
> With many thousands of references, a simple `git rev-parse HEAD` may take
> more than a second to return because it first loads all the refs into
> memory even though it will never use them.
The overall goal of lazy-loading seems reasonable, but I'm slightly
confused: how and why does "git rev-parse HEAD" load ref decorations?
Grepping around I find that we mostly load them only when appropriate
(when the "log" family sees a decorate option, when we see %d/%D in a
pretty format, or with --simplify-by-decoration in a traversal). And
poking at "rev-parse HEAD" in gdb seems to confirm that it does not hit
that function.
I have definitely seen "rev-parse HEAD" be O(# of refs), but that is
mostly attributable to having all the refs packed (and until v2.15.0,
the packed-refs code would read the whole file into memory). I've also
seen unnecessary ref lookups due to replace refs (we load al of the
packed refs to find out that no, there's nothing in refs/replace).
-Peff
next prev parent reply other threads:[~2017-11-22 21:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-21 23:43 [PATCH] defer expensive load_ref_decorations until needed Phil Hord
2017-11-22 5:03 ` Junio C Hamano
2017-11-22 6:14 ` Junio C Hamano
2017-11-22 17:45 ` Phil Hord
2017-11-22 21:27 ` Jeff King [this message]
2017-11-22 23:21 ` Phil Hord
2017-11-22 23:48 ` Jeff King
2017-11-23 2:19 ` Junio C Hamano
2017-11-23 4:00 ` Jeff King
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