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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Tom Clarkson via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Avery Pennarun <apenwarr@gmail.com>,
	Ed Maste <emaste@freebsd.org>, Tom Clarkson <tom@tqclarkson.com>
Subject: Re: [PATCH v2 0/7] subtree: Fix handling of complex history
Date: Wed, 7 Oct 2020 21:46:36 +0200 (CEST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.2010072143390.50@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <pull.493.v2.git.1602021913.gitgitgadget@gmail.com>

Hi Tom,

On Tue, 6 Oct 2020, Tom Clarkson via GitGitGadget wrote:

> Fixes several issues that could occur when running subtree split on large
> repos with more complex history.
>
>  1. A merge commit could bypass the known start point of the subtree, which
>     would cause the entire history to be processed recursively, leading to a
>     stack overflow / segfault after reading a few hundred commits. Older
>     commits are now explicitly recorded as irrelevant so that the recursive
>     process can terminate on any mainline commit rather than only on subtree
>     joins and initial commits.
>
>
>  2. It is possible for a repo to contain subtrees that lack the metadata
>     that is usually present in add/join commit messages (git-svn at least
>     can produce such a structure). The new use/ignore/map commands allow the
>     user to provide that information for any problematic commits.
>
>
>  3. A mainline commit that does not contain the subtree folder could be
>     erroneously identified as a subtree commit, which would add the entire
>     mainline history to the subtree. Commits will now only be used as is if
>     all their parents are already identified as subtree commits. While the
>     new code can still be tripped up by unusual folder structures, the
>     completely unambiguous solution turned out to involve a significant
>     performance penalty, and the new ignore / use commands provide a
>     workaround for that scenario.

I gave this as thorough a review as I can (which is not saying too much,
as I am not exactly familiar with `git subtree`'s inner workings).

Hopefully some of my comments and suggestions are helpful.

At some stage, especially given the problems I pointed out with the
implementation detail that is a flat directory with a potentially insane
number of files in it, I think it would make a lot of sense to go ahead
and turn this into a built-in Git command, implemented in C, and with a
more robust file system layout of its cache.

Ciao,
Dscho

      parent reply	other threads:[~2020-10-07 19:46 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-11  5:49 [PATCH 0/7] subtree: Fix handling of complex history Tom Clarkson via GitGitGadget
2020-05-11  5:49 ` [PATCH 1/7] subtree: handle multiple parents passed to cache_miss Tom Clarkson via GitGitGadget
2020-05-11  5:49 ` [PATCH 2/7] subtree: exclude commits predating add from recursive processing Tom Clarkson via GitGitGadget
2020-05-11  5:49 ` [PATCH 3/7] subtree: persist cache between split runs Tom Clarkson via GitGitGadget
2020-05-11  5:49 ` [PATCH 4/7] subtree: add git subtree map command Tom Clarkson via GitGitGadget
2020-05-11  5:49 ` [PATCH 5/7] subtree: add git subtree use and ignore commands Tom Clarkson via GitGitGadget
2020-05-11  5:50 ` [PATCH 6/7] subtree: more robustly distinguish subtree and mainline commits Tom Clarkson via GitGitGadget
2020-05-11  5:50 ` [PATCH 7/7] subtree: document new subtree commands Tom Clarkson via GitGitGadget
2020-10-04 17:52 ` [PATCH 0/7] subtree: Fix handling of complex history Ed Maste
2020-10-04 19:27   ` Johannes Schindelin
2020-10-05 16:47     ` Junio C Hamano
2020-10-05 21:37     ` Ed Maste
2020-10-07 16:31       ` Johannes Schindelin
2020-10-06 22:05 ` [PATCH v2 " Tom Clarkson via GitGitGadget
2020-10-06 22:05   ` [PATCH v2 1/7] subtree: handle multiple parents passed to cache_miss Tom Clarkson via GitGitGadget
2020-10-07 13:12     ` Ed Maste
2020-10-06 22:05   ` [PATCH v2 2/7] subtree: exclude commits predating add from recursive processing Tom Clarkson via GitGitGadget
2020-10-07 15:36     ` Johannes Schindelin
2020-10-06 22:05   ` [PATCH v2 3/7] subtree: persist cache between split runs Tom Clarkson via GitGitGadget
2020-10-07 16:06     ` Johannes Schindelin
2020-10-06 22:05   ` [PATCH v2 4/7] subtree: add git subtree map command Tom Clarkson via GitGitGadget
2020-10-06 22:05   ` [PATCH v2 5/7] subtree: add git subtree use and ignore commands Tom Clarkson via GitGitGadget
2020-10-07 16:29     ` Johannes Schindelin
2020-10-06 22:05   ` [PATCH v2 6/7] subtree: more robustly distinguish subtree and mainline commits Tom Clarkson via GitGitGadget
2020-10-07 19:42     ` Johannes Schindelin
2020-10-06 22:05   ` [PATCH v2 7/7] subtree: document new subtree commands Tom Clarkson via GitGitGadget
2020-10-07 19:43     ` Johannes Schindelin
2020-10-07 19:46   ` Johannes Schindelin [this message]

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