# Question about git-merge-stupid 7 messages from 2008-07-03 to 2008-07-05. Participants: Miklos Vajna, Linus Torvalds, Junio C Hamano. Thread: https://gitlist.dev/t/14275 ## Miklos Vajna, 2008-07-03 12:33 Subject: Question about git-merge-stupid Message-ID: <20080703123314.GS4729@genesis.frugalware.org> URL: https://gitlist.dev/e/20080703123314.GS4729%40genesis.frugalware.org ``` Hi, I'm trying to understand what is the difference between different merge strategies. git-merge-stupid is something I failed to understand from the git history/code/documentation, so I'm asking here. 1) From git history: It seems git-merge-stupid was created by 2276aa6 when Junio renamed -resolve to -stupid and let -resolve use read-tree. Actually git show 2276aa6:git-merge-stupid.sh says -stupid uses read-tree as well. 2) From code: It seems -stupid is better than -resolve when there are multiple bases. -resolve just passes all bases to read-tree, while -stupid tries to find the best one. It does it by counting unmerged entries and the less one is a better. Here is what I tried: A - B - C X \ \ D - E - F (Where 'A' adds 'a.c' while the contents 'a', etc.) $ git reset --hard e $ git merge -s resolve c Trying simple merge. Merge made by resolve. So it seems resolve does not completely fail if there are multiple bases, either. I would like to write a testcase that ensures git-merge-stupid really picks the best base, but I don't know exactly in what situation can the number of unmerged entires differ. 3) From documentation: Actually -stupid is missing from Documentation/merge-strategies.txt. I plan to send a patch to add it, once I understnad what it does. :-) Thanks. [ Writing to Linus as suggested by Dscho, adding Junio to CC as - according to git log - both strategy created by him. ] ``` ## Linus Torvalds, 2008-07-03 17:08 Subject: Re: Question about git-merge-stupid Message-ID: URL: https://gitlist.dev/e/alpine.LFD.1.10.0807030947360.18105%40woody.linux-foundation.org In-Reply-To: <20080703123314.GS4729@genesis.frugalware.org> ``` On Thu, 3 Jul 2008, Miklos Vajna wrote: > > I'm trying to understand what is the difference between different merge > strategies. git-merge-stupid is something I failed to understand from > the git history/code/documentation, so I'm asking here. > > 1) From git history: > > It seems git-merge-stupid was created by 2276aa6 when Junio renamed > -resolve to -stupid and let -resolve use read-tree. Actually > > git show 2276aa6:git-merge-stupid.sh > > says -stupid uses read-tree as well. I think -stupid should probably be removed. The history of -stupid is from doing the simple single-tree resolve that git-read-tree can do, but then doing the obvious hack of just trying to pick the base that gives the least number of conflicts. HOWEVER. - in practice, there's seldom any actual point to it. In 99% of all cases, you only have a single merge base anyway. - if you have a workflow that encourages criss-cross merges (which makes the above "in practice" not be true), the common case will be that the merge base doesn't much matter. - Counting conflicts by looking at the numbe of files that conflict is a pretty stupid metric anyway. Yes, it's obvious, and yes, I bet there are cases where it does the right thing, but I also bet there are cases where it does the _wrong_ thing - it might pick a merge base with fewer files conflicting, but with harder conflicts. - the "recursive" merge strategy simply handles things better. There's not really any reason to use a "pick random merge base that happens to give least conflicts", when the recursive strategy does something much more natural. So you shouldn't really compare -stupid to -resolve. You should compare -stupid to -recursive, and the latter is simply much better. > 2) From code: > > It seems -stupid is better than -resolve when there are multiple bases. Maybe. And maybe not. > $ git merge -s resolve c > Trying simple merge. > Merge made by resolve. > > So it seems resolve does not completely fail if there are multiple > bases, either. I think -resolve can handle up to 6 bases, or something like that. After that it should fail with a "I cannot read more than 8 trees" or something (eight being the two trees to be merged, plus the six bases). And with multiple bases, it will already pick the best one on a per-file basis (I think - I should know the threeway merge, but it is pretty confusing code) rather than trying to pick one globally. Not pretty, but it's yet another reason why -stupid is actually stupid, and not worth it. So -stupid in _theory_ can handle cases that -resolve cannot (more than six bases), but (a) that doesn't happen and (b) you'd be better off with -recursive anyway. > 3) From documentation: > > Actually -stupid is missing from Documentation/merge-strategies.txt. I > plan to send a patch to add it, once I understnad what it does. :-) Well, see above. I think there's a reason why -stupid isn't even worth documenting. It might be better off just removed. Linus ``` ## Miklos Vajna, 2008-07-03 23:18 Subject: [RFC/PATCH] Remove 'stupid' merge strategy. Message-ID: <1215127101-14932-1-git-send-email-vmiklos@frugalware.org> URL: https://gitlist.dev/e/1215127101-14932-1-git-send-email-vmiklos%40frugalware.org In-Reply-To: ``` As pointed out by Linus, this strategy tries to take the best merge base, but 'recursive' just does it better. If one needs something more than 'resolve' then he/she should really use 'recursive' and not 'stupid'. --- On Thu, Jul 03, 2008 at 10:08:54AM -0700, Linus Torvalds wrote: > I think -stupid should probably be removed. Here is an attempt to do so. > The history of -stupid is from doing the simple single-tree resolve > that > git-read-tree can do, but then doing the obvious hack of just trying > to > pick the base that gives the least number of conflicts. > > HOWEVER. > > (...) Thanks for the detailed answer. .gitignore | 1 - Makefile | 3 +- git-merge-stupid.sh | 80 --------------------------------------------------- 3 files changed, 1 insertions(+), 83 deletions(-) delete mode 100755 git-merge-stupid.sh diff --git a/.gitignore b/.gitignore index 4ff2fec..8054d9d 100644 --- a/.gitignore +++ b/.gitignore @@ -75,7 +75,6 @@ git-merge-one-file git-merge-ours git-merge-recursive git-merge-resolve -git-merge-stupid git-merge-subtree git-mergetool git-mktag diff --git a/Makefile b/Makefile index 78e08d3..bddd1a7 100644 --- a/Makefile +++ b/Makefile @@ -241,7 +241,6 @@ SCRIPT_SH += git-merge-octopus.sh SCRIPT_SH += git-merge-one-file.sh SCRIPT_SH += git-merge-resolve.sh SCRIPT_SH += git-merge.sh -SCRIPT_SH += git-merge-stupid.sh SCRIPT_SH += git-mergetool.sh SCRIPT_SH += git-parse-remote.sh SCRIPT_SH += git-pull.sh @@ -1429,7 +1428,7 @@ check-docs:: do \ case "$$v" in \ git-merge-octopus | git-merge-ours | git-merge-recursive | \ - git-merge-resolve | git-merge-stupid | git-merge-subtree | \ + git-merge-resolve | git-merge-subtree | \ git-fsck-objects | git-init-db | \ git-?*--?* ) continue ;; \ esac ; \ diff --git a/git-merge-stupid.sh b/git-merge-stupid.sh deleted file mode 100755 index f612d47..0000000 --- a/git-merge-stupid.sh +++ /dev/null @@ -1,80 +0,0 @@ -#!/bin/sh -# -# Copyright (c) 2005 Linus Torvalds -# -# Resolve two trees, 'stupid merge'. - -# The first parameters up to -- are merge bases; the rest are heads. -bases= head= remotes= sep_seen= -for arg -do - case ",$sep_seen,$head,$arg," in - *,--,) - sep_seen=yes - ;; - ,yes,,*) - head=$arg - ;; - ,yes,*) - remotes="$remotes$arg " - ;; - *) - bases="$bases$arg " - ;; - esac -done - -# Give up if we are given two or more remotes -- not handling octopus. -case "$remotes" in -?*' '?*) - exit 2 ;; -esac - -# Find an optimum merge base if there are more than one candidates. -case "$bases" in -?*' '?*) - echo "Trying to find the optimum merge base." - G=.tmp-index$$ - best= - best_cnt=-1 - for c in $bases - do - rm -f $G - GIT_INDEX_FILE=$G git read-tree -m $c $head $remotes \ - 2>/dev/null || continue - # Count the paths that are unmerged. - cnt=`GIT_INDEX_FILE=$G git ls-files --unmerged | wc -l` - if test $best_cnt -le 0 -o $cnt -le $best_cnt - then - best=$c - best_cnt=$cnt - if test "$best_cnt" -eq 0 - then - # Cannot do any better than all trivial merge. - break - fi - fi - done - rm -f $G - common="$best" - ;; -*) - common="$bases" - ;; -esac - -git update-index --refresh 2>/dev/null -git read-tree -u -m $common $head $remotes || exit 2 -echo "Trying simple merge." -if result_tree=$(git write-tree 2>/dev/null) -then - exit 0 -else - echo "Simple merge failed, trying Automatic merge." - if git-merge-index -o git-merge-one-file -a - then - exit 0 - else - exit 1 - fi -fi -- 1.5.6.1 ``` ## Junio C Hamano, 2008-07-03 23:54 Subject: Re: Question about git-merge-stupid Message-ID: <7v4p76y154.fsf@gitster.siamese.dyndns.org> URL: https://gitlist.dev/e/7v4p76y154.fsf%40gitster.siamese.dyndns.org In-Reply-To: ``` Linus Torvalds writes: > Well, see above. I think there's a reason why -stupid isn't even worth > documenting. It might be better off just removed. It is called stupid for a reason ;-). It has been sitting there as an example for a long time, and I do not think anybody minds removing it. ``` ## Miklos Vajna, 2008-07-04 00:07 Subject: Re: Question about git-merge-stupid Message-ID: <20080704000701.GX4729@genesis.frugalware.org> URL: https://gitlist.dev/e/20080704000701.GX4729%40genesis.frugalware.org In-Reply-To: <7v4p76y154.fsf@gitster.siamese.dyndns.org> ``` On Thu, Jul 03, 2008 at 04:54:31PM -0700, Junio C Hamano wrote: > It is called stupid for a reason ;-). > > It has been sitting there as an example for a long time, and I do > not think anybody minds removing it. OK, then should I resend a patch that moves it to contrib/examples? ``` ## Miklos Vajna, 2008-07-05 14:43 Subject: [PATCH] Move 'stupid' merge strategy to contrib. Message-ID: <1215269031-19559-1-git-send-email-vmiklos@frugalware.org> URL: https://gitlist.dev/e/1215269031-19559-1-git-send-email-vmiklos%40frugalware.org In-Reply-To: <20080704000701.GX4729@genesis.frugalware.org> ``` As pointed out by Linus, this strategy tries to take the best merge base, but 'recursive' just does it better. If one needs something more than 'resolve' then he/she should really use 'recursive' and not 'stupid'. Given that it may still serve as a good example, don't remove it, just move it to contrib/examples. --- On Fri, Jul 04, 2008 at 02:07:01AM +0200, Miklos Vajna wrote: > On Thu, Jul 03, 2008 at 04:54:31PM -0700, Junio C Hamano > wrote: > > It is called stupid for a reason ;-). > > > > It has been sitting there as an example for a long time, and I do > > not think anybody minds removing it. > > OK, then should I resend a patch that moves it to contrib/examples? Here is one. .gitignore | 1 - Makefile | 3 +- contrib/examples/git-merge-stupid.sh | 80 ++++++++++++++++++++++++++++++++++ git-merge-stupid.sh | 80 ---------------------------------- 4 files changed, 81 insertions(+), 83 deletions(-) create mode 100755 contrib/examples/git-merge-stupid.sh delete mode 100755 git-merge-stupid.sh diff --git a/.gitignore b/.gitignore index 4ff2fec..8054d9d 100644 --- a/.gitignore +++ b/.gitignore @@ -75,7 +75,6 @@ git-merge-one-file git-merge-ours git-merge-recursive git-merge-resolve -git-merge-stupid git-merge-subtree git-mergetool git-mktag diff --git a/Makefile b/Makefile index 78e08d3..bddd1a7 100644 --- a/Makefile +++ b/Makefile @@ -241,7 +241,6 @@ SCRIPT_SH += git-merge-octopus.sh SCRIPT_SH += git-merge-one-file.sh SCRIPT_SH += git-merge-resolve.sh SCRIPT_SH += git-merge.sh -SCRIPT_SH += git-merge-stupid.sh SCRIPT_SH += git-mergetool.sh SCRIPT_SH += git-parse-remote.sh SCRIPT_SH += git-pull.sh @@ -1429,7 +1428,7 @@ check-docs:: do \ case "$$v" in \ git-merge-octopus | git-merge-ours | git-merge-recursive | \ - git-merge-resolve | git-merge-stupid | git-merge-subtree | \ + git-merge-resolve | git-merge-subtree | \ git-fsck-objects | git-init-db | \ git-?*--?* ) continue ;; \ esac ; \ diff --git a/contrib/examples/git-merge-stupid.sh b/contrib/examples/git-merge-stupid.sh new file mode 100755 index 0000000..f612d47 --- /dev/null +++ b/contrib/examples/git-merge-stupid.sh @@ -0,0 +1,80 @@ +#!/bin/sh +# +# Copyright (c) 2005 Linus Torvalds +# +# Resolve two trees, 'stupid merge'. + +# The first parameters up to -- are merge bases; the rest are heads. +bases= head= remotes= sep_seen= +for arg +do + case ",$sep_seen,$head,$arg," in + *,--,) + sep_seen=yes + ;; + ,yes,,*) + head=$arg + ;; + ,yes,*) + remotes="$remotes$arg " + ;; + *) + bases="$bases$arg " + ;; + esac +done + +# Give up if we are given two or more remotes -- not handling octopus. +case "$remotes" in +?*' '?*) + exit 2 ;; +esac + +# Find an optimum merge base if there are more than one candidates. +case "$bases" in +?*' '?*) + echo "Trying to find the optimum merge base." + G=.tmp-index$$ + best= + best_cnt=-1 + for c in $bases + do + rm -f $G + GIT_INDEX_FILE=$G git read-tree -m $c $head $remotes \ + 2>/dev/null || continue + # Count the paths that are unmerged. + cnt=`GIT_INDEX_FILE=$G git ls-files --unmerged | wc -l` + if test $best_cnt -le 0 -o $cnt -le $best_cnt + then + best=$c + best_cnt=$cnt + if test "$best_cnt" -eq 0 + then + # Cannot do any better than all trivial merge. + break + fi + fi + done + rm -f $G + common="$best" + ;; +*) + common="$bases" + ;; +esac + +git update-index --refresh 2>/dev/null +git read-tree -u -m $common $head $remotes || exit 2 +echo "Trying simple merge." +if result_tree=$(git write-tree 2>/dev/null) +then + exit 0 +else + echo "Simple merge failed, trying Automatic merge." + if git-merge-index -o git-merge-one-file -a + then + exit 0 + else + exit 1 + fi +fi diff --git a/git-merge-stupid.sh b/git-merge-stupid.sh deleted file mode 100755 index f612d47..0000000 --- a/git-merge-stupid.sh +++ /dev/null @@ -1,80 +0,0 @@ -#!/bin/sh -# -# Copyright (c) 2005 Linus Torvalds -# -# Resolve two trees, 'stupid merge'. - -# The first parameters up to -- are merge bases; the rest are heads. -bases= head= remotes= sep_seen= -for arg -do - case ",$sep_seen,$head,$arg," in - *,--,) - sep_seen=yes - ;; - ,yes,,*) - head=$arg - ;; - ,yes,*) - remotes="$remotes$arg " - ;; - *) - bases="$bases$arg " - ;; - esac -done - -# Give up if we are given two or more remotes -- not handling octopus. -case "$remotes" in -?*' '?*) - exit 2 ;; -esac - -# Find an optimum merge base if there are more than one candidates. -case "$bases" in -?*' '?*) - echo "Trying to find the optimum merge base." - G=.tmp-index$$ - best= - best_cnt=-1 - for c in $bases - do - rm -f $G - GIT_INDEX_FILE=$G git read-tree -m $c $head $remotes \ - 2>/dev/null || continue - # Count the paths that are unmerged. - cnt=`GIT_INDEX_FILE=$G git ls-files --unmerged | wc -l` - if test $best_cnt -le 0 -o $cnt -le $best_cnt - then - best=$c - best_cnt=$cnt - if test "$best_cnt" -eq 0 - then - # Cannot do any better than all trivial merge. - break - fi - fi - done - rm -f $G - common="$best" - ;; -*) - common="$bases" - ;; -esac - -git update-index --refresh 2>/dev/null -git read-tree -u -m $common $head $remotes || exit 2 -echo "Trying simple merge." -if result_tree=$(git write-tree 2>/dev/null) -then - exit 0 -else - echo "Simple merge failed, trying Automatic merge." - if git-merge-index -o git-merge-one-file -a - then - exit 0 - else - exit 1 - fi -fi -- 1.5.6.1.322.ge904b.dirty ``` ## Miklos Vajna, 2008-07-05 21:00 Subject: [PATCH] Move 'stupid' merge strategy to contrib. Message-ID: <1215291607-20781-1-git-send-email-vmiklos@frugalware.org> URL: https://gitlist.dev/e/1215291607-20781-1-git-send-email-vmiklos%40frugalware.org In-Reply-To: <1215269031-19559-1-git-send-email-vmiklos@frugalware.org> ``` As pointed out by Linus, this strategy tries to take the best merge base, but 'recursive' just does it better. If one needs something more than 'resolve' then he/she should really use 'recursive' and not 'stupid'. Given that it may still serve as a good example, don't remove it, just move it to contrib/examples. --- n Sat, Jul 05, 2008 at 04:43:51PM +0200, Miklos Vajna wrote: > Here is one. Oops, I forgot -M with format-patch. .gitignore | 1 - Makefile | 3 +-- .../examples/git-merge-stupid.sh | 0 3 files changed, 1 insertions(+), 3 deletions(-) rename git-merge-stupid.sh => contrib/examples/git-merge-stupid.sh (100%) diff --git a/.gitignore b/.gitignore index 4ff2fec..8054d9d 100644 --- a/.gitignore +++ b/.gitignore @@ -75,7 +75,6 @@ git-merge-one-file git-merge-ours git-merge-recursive git-merge-resolve -git-merge-stupid git-merge-subtree git-mergetool git-mktag diff --git a/Makefile b/Makefile index 78e08d3..bddd1a7 100644 --- a/Makefile +++ b/Makefile @@ -241,7 +241,6 @@ SCRIPT_SH += git-merge-octopus.sh SCRIPT_SH += git-merge-one-file.sh SCRIPT_SH += git-merge-resolve.sh SCRIPT_SH += git-merge.sh -SCRIPT_SH += git-merge-stupid.sh SCRIPT_SH += git-mergetool.sh SCRIPT_SH += git-parse-remote.sh SCRIPT_SH += git-pull.sh @@ -1429,7 +1428,7 @@ check-docs:: do \ case "$$v" in \ git-merge-octopus | git-merge-ours | git-merge-recursive | \ - git-merge-resolve | git-merge-stupid | git-merge-subtree | \ + git-merge-resolve | git-merge-subtree | \ git-fsck-objects | git-init-db | \ git-?*--?* ) continue ;; \ esac ; \ diff --git a/git-merge-stupid.sh b/contrib/examples/git-merge-stupid.sh similarity index 100% rename from git-merge-stupid.sh rename to contrib/examples/git-merge-stupid.sh -- 1.5.6.1.322.ge904b.dirty ```