| Message ID | pull.493.v2.git.1602021913.gitgitgadget@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | subtree: Fix handling of complex history | expand |
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
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. Tom Clarkson (7): subtree: handle multiple parents passed to cache_miss subtree: exclude commits predating add from recursive processing subtree: persist cache between split runs subtree: add git subtree map command subtree: add git subtree use and ignore commands subtree: more robustly distinguish subtree and mainline commits subtree: document new subtree commands contrib/subtree/git-subtree.sh | 183 ++++++++++++++++++++++++++------ contrib/subtree/git-subtree.txt | 24 +++++ 2 files changed, 175 insertions(+), 32 deletions(-) base-commit: 47ae905ffb98cc4d4fd90083da6bc8dab55d9ecc Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-493%2Ftqc%2Ftqc%2Fsubtree-v2 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-493/tqc/tqc/subtree-v2 Pull-Request: https://github.com/gitgitgadget/git/pull/493 Range-diff vs v1: 1: 74fa670490 = 1: 9cff2a0cf6 subtree: handle multiple parents passed to cache_miss 2: 87af5a316a ! 2: 79b5f4a651 subtree: exclude commits predating add from recursive processing @@ contrib/subtree/git-subtree.sh: find_existing_splits () { + debug "Looking for first split..." + dir="$1" + revs="$2" -+ main= -+ sub= -+ local grep_format="^git-subtree-dir: $dir/*\$" -+ git log --reverse --grep="$grep_format" \ ++ ++ git log --reverse --grep="^git-subtree-dir: $dir/*\$" \ + --no-show-signature --pretty=format:'START %H%n%s%n%n%b%nEND%n' $revs | + while read a b junk + do 3: c892ee9828 = 3: 8eec18388c subtree: persist cache between split runs 4: a67c256a59 = 4: 1490ce1114 subtree: add git subtree map command 5: a76a49651b = 5: 2d103292ce subtree: add git subtree use and ignore commands 6: 27a43ea2c4 = 6: a7aaedfed3 subtree: more robustly distinguish subtree and mainline commits 7: 19db9cfb68 = 7: fe2e4819b8 subtree: document new subtree commands