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This patch linearises the GIT commit history graph into merge order
which is defined by invariants specified in Documentation/git-rev-list.txt.
The linearisation produced by this patch is superior in an objective sense
to that produced by the existing git-rev-list implementation in that
the linearisation produced is guaranteed to have the minimum number of
discontinuities, where a discontinuity is defined as an adjacent pair of
commits in the output list which are not related in a direct child-parent
relationship.
With this patch a graph like this:
a4 ---
| \ \
| b4 |
|/ | |
a3 | |
| | |
a2 | |
| | c3
| | |
| | c2
| b3 |
| | /|
| b2 |
| | c1
| | /
| b1
a1 |
| |
a0 |
| /
root
Sorts like this:
= a4
| c3
| c2
| c1
^ b4
| b3
| b2
| b1
^ a3
| a2
| a1
| a0
= root
Instead of this:
= a4
| c3
^ b4
| a3
^ c2
^ b3
^ a2
^ b2
^ c1
^ a1
^ b1
^ a0
= root
A test script, t/t6000-rev-list.sh, includes a test which demonstrates
that the linearisation produced by --merge-order has less discontinuities
than the linearisation produced by git-rev-list without the --merge-order
flag specified. To see this, do the following:
cd t
./t6000-rev-list.sh
cd trash
cat actual-default-order
cat actual-merge-order
The existing behaviour of git-rev-list is preserved, by default. To obtain
the modified behaviour, specify --merge-order or --merge-order --show-breaks
on the command line.
This version of the patch has been tested on the git repository and also on the linux-2.6
repository and has reasonable performance on both - ~50-100% slower than the original algorithm.
This version of the patch has incorporated a functional equivalent of the Linus' output limiting
algorithm into the merge-order algorithm itself. This operates per the notes associated
with Linus' commit 337cb3fb8d.
This version has incorporated Linus' feedback regarding proposed changes to rev-list.c.
(see: [PATCH] Factor out filtering in rev-list.c)
This version has improved the way sort_first_epoch marks commits as uninteresting.
For more details about this change, refer to Documentation/git-rev-list.txt
and http://blackcubes.dyndns.org/epoch/.
Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
61 lines
2.6 KiB
Plaintext
61 lines
2.6 KiB
Plaintext
git-rev-list(1)
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===============
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v0.1, May 2005
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NAME
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----
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git-rev-list - Lists commit objects in reverse chronological order
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SYNOPSIS
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--------
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'git-rev-list' [ *--max-count*=number ] [ *--max-age*=timestamp ] [ *--min-age*=timestamp ] [ *--merge-order* [ *--show-breaks* ] ] <commit>
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DESCRIPTION
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-----------
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Lists commit objects in reverse chronological order starting at the
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given commit, taking ancestry relationship into account. This is
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useful to produce human-readable log output.
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If *--merge-order* is specified, the commit history is decomposed into a unique sequence of minimal, non-linear
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epochs and maximal, linear epochs. Non-linear epochs are then linearised by sorting them into merge order, which
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is described below.
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Maximal, linear epochs correspond to periods of sequential development. Minimal, non-linear epochs
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correspond to periods of divergent development followed by a converging merge. The theory of epochs is described
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in more detail at link:http://blackcubes.dyndns.org/epoch/[http://blackcubes.dyndns.org/epoch/].
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The merge order for a non-linear epoch is defined as a linearisation for which the following invariants are true:
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1. if a commit P is reachable from commit N, commit P sorts after commit N in the linearised list.
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2. if Pi and Pj are any two parents of a merge M (with i < j), then any commit N, such that N is reachable from Pj
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but not reachable from Pi, sorts before all commits reachable from Pi.
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Invariant 1 states that later commits appear before earlier commits they are derived from.
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Invariant 2 states that commits unique to "later" parents in a merge, appear before all commits from "earlier" parents of
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a merge.
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If *--show-breaks* is specified, each item of the list is output with a 2-character prefix consisting of one of:
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(|), (^), (=) followed by a space.
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Commits marked with (=) represent the boundaries of minimal, non-linear epochs and correspond either to the start of a period of divergent development or to the end of such a period.
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Commits marked with (|) are direct parents of commits immediately preceding the marked commit in the list.
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Commits marked with (^) are not parents of the immediately preceding commit. These "breaks" represent necessary discontinuities implied by trying to represent an arbtirary DAG in a linear form.
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*--show-breaks* is only valid if *--merge-order* is also specified.
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Author
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------
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Written by Linus Torvalds <torvalds@osdl.org>
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Original *--merge-order* logic by Jon Seymour <jon.seymour@gmail.com>
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Documentation
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--------------
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Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
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GIT
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---
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Part of the link:git.html[git] suite
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