Documentation/merge-strategies.adoc - git - Git at Google

 MERGE STRATEGIES
 ----------------

 The merge mechanism (`git merge` and `git pull` commands) allows the
 backend 'merge strategies' to be chosen with `-s` option.  Some strategies
 can also take their own options, which can be passed by giving `-X<option>`
 arguments to `git merge` and/or `git pull`.

 `ort`::
 	This is the default merge strategy when pulling or merging one
 	branch.  This strategy can only resolve two heads using a
 	3-way merge algorithm.  When there is more than one common
 	ancestor that can be used for 3-way merge, it creates a merged
 	tree of the common ancestors and uses that as the reference
 	tree for the 3-way merge.  This has been reported to result in
 	fewer merge conflicts without causing mismerges by tests done
 	on actual merge commits taken from Linux 2.6 kernel
 	development history.  Additionally this strategy can detect
 	and handle merges involving renames.  It does not make use of
 	detected copies.  The name for this algorithm is an acronym
 	("Ostensibly Recursive's Twin") and came from the fact that it
 	was written as a replacement for the previous default
 	algorithm, `recursive`.
 +
 In the case where the path is a submodule, if the submodule commit used on
 one side of the merge is a descendant of the submodule commit used on the
 other side of the merge, Git attempts to fast-forward to the
 descendant. Otherwise, Git will treat this case as a conflict, suggesting
 as a resolution a submodule commit that is descendant of the conflicting
 ones, if one exists.
 +
 The `ort` strategy can take the following options:

 `ours`;;
 	This option forces conflicting hunks to be auto-resolved cleanly by
 	favoring 'our' version.  Changes from the other tree that do not
 	conflict with our side are reflected in the merge result.
 	For a binary file, the entire contents are taken from our side.
 +
 This should not be confused with the `ours` merge strategy, which does not
 even look at what the other tree contains at all.  It discards everything
 the other tree did, declaring 'our' history contains all that happened in it.

 `theirs`;;
 	This is the opposite of `ours`; note that, unlike `ours`, there is
 	no `theirs` merge strategy to confuse this merge option with.

 `ignore-space-change`;;
 `ignore-all-space`;;
 `ignore-space-at-eol`;;
 `ignore-cr-at-eol`;;
 	Treats lines with the indicated type of whitespace change as
 	unchanged for the sake of a three-way merge.  Whitespace
 	changes mixed with other changes to a line are not ignored.
 	See also linkgit:git-diff[1] `-b`, `-w`,
 	`--ignore-space-at-eol`, and `--ignore-cr-at-eol`.
 +
 * If 'their' version only introduces whitespace changes to a line,
   'our' version is used;
 * If 'our' version introduces whitespace changes but 'their'
   version includes a substantial change, 'their' version is used;
 * Otherwise, the merge proceeds in the usual way.

 `renormalize`;;
 	This runs a virtual check-out and check-in of all three stages
 	of any file which needs a three-way merge.  This option is
 	meant to be used when merging branches with different clean
 	filters or end-of-line normalization rules.  See "Merging
 	branches with differing checkin/checkout attributes" in
 	linkgit:gitattributes[5] for details.

 `no-renormalize`;;
 	Disables the `renormalize` option.  This overrides the
 	`merge.renormalize` configuration variable.

 `find-renames[=<n>]`;;
 	Turn on rename detection, optionally setting the similarity
 	threshold.  This is the default. This overrides the
 	`merge.renames` configuration variable.
 	See also linkgit:git-diff[1] `--find-renames`.

 `rename-threshold=<n>`;;
 	Deprecated synonym for `find-renames=<n>`.

 `no-renames`;;
 	Turn off rename detection. This overrides the `merge.renames`
 	configuration variable.
 	See also linkgit:git-diff[1] `--no-renames`.

 `histogram`;;
 	Deprecated synonym for `diff-algorithm=histogram`.

 `patience`;;
 	Deprecated synonym for `diff-algorithm=patience`.

 `diff-algorithm=(histogram|minimal|myers|patience)`;;
 	Use a different diff algorithm while merging, which can help
 	avoid mismerges that occur due to unimportant matching lines
 	(such as braces from distinct functions).  See also
 	linkgit:git-diff[1] `--diff-algorithm`.  Note that `ort`
 	defaults to `diff-algorithm=histogram`, while regular diffs
 	currently default to the `diff.algorithm` config setting.

 `subtree[=<path>]`;;
 	This option is a more advanced form of 'subtree' strategy, where
 	the strategy makes a guess on how two trees must be shifted to
 	match with each other when merging.  Instead, the specified path
 	is prefixed (or stripped from the beginning) to make the shape of
 	two trees to match.

 `recursive`::
 	This is now a synonym for `ort`.  It was an alternative
 	implementation until v2.49.0, but was redirected to mean `ort`
 	in v2.50.0.  The previous recursive strategy was the default
 	strategy for resolving two heads from Git v0.99.9k until
 	v2.33.0.

 `resolve`::
 	This can only resolve two heads (i.e. the current branch
 	and another branch you pulled from) using a 3-way merge
 	algorithm.  It tries to carefully detect criss-cross
 	merge ambiguities.  It does not handle renames.

 `octopus`::
 	This resolves cases with more than two heads, but refuses to do
 	a complex merge that needs manual resolution.  It is
 	primarily meant to be used for bundling topic branch
 	heads together.  This is the default merge strategy when
 	pulling or merging more than one branch.

 `ours`::
 	This resolves any number of heads, but the resulting tree of the
 	merge is always that of the current branch head, effectively
 	ignoring all changes from all other branches.  It is meant to
 	be used to supersede old development history of side
 	branches.  Note that this is different from the `-Xours` option to
 	the `ort` merge strategy.

 `subtree`::
 	This is a modified `ort` strategy. When merging trees A and
 	B, if B corresponds to a subtree of A, B is first adjusted to
 	match the tree structure of A, instead of reading the trees at
 	the same level. This adjustment is also done to the common
 	ancestor tree.

 With the strategies that use 3-way merge (including the default, `ort`),
 if a change is made on both branches, but later reverted on one of the
 branches, that change will be present in the merged result; some people find
 this behavior confusing.  It occurs because only the heads and the merge base
 are considered when performing a merge, not the individual commits.  The merge
 algorithm therefore considers the reverted change as no change at all, and
 substitutes the changed version instead.
	MERGE STRATEGIES
	----------------

	The merge mechanism (`git merge` and `git pull` commands) allows the
	backend 'merge strategies' to be chosen with `-s` option. Some strategies
	can also take their own options, which can be passed by giving `-X<option>`
	arguments to `git merge` and/or `git pull`.

	`ort`::
	This is the default merge strategy when pulling or merging one
	branch. This strategy can only resolve two heads using a
	3-way merge algorithm. When there is more than one common
	ancestor that can be used for 3-way merge, it creates a merged
	tree of the common ancestors and uses that as the reference
	tree for the 3-way merge. This has been reported to result in
	fewer merge conflicts without causing mismerges by tests done
	on actual merge commits taken from Linux 2.6 kernel
	development history. Additionally this strategy can detect
	and handle merges involving renames. It does not make use of
	detected copies. The name for this algorithm is an acronym
	("Ostensibly Recursive's Twin") and came from the fact that it
	was written as a replacement for the previous default
	algorithm, `recursive`.
	+
	In the case where the path is a submodule, if the submodule commit used on
	one side of the merge is a descendant of the submodule commit used on the
	other side of the merge, Git attempts to fast-forward to the
	descendant. Otherwise, Git will treat this case as a conflict, suggesting
	as a resolution a submodule commit that is descendant of the conflicting
	ones, if one exists.
	+
	The `ort` strategy can take the following options:

	`ours`;;
	This option forces conflicting hunks to be auto-resolved cleanly by
	favoring 'our' version. Changes from the other tree that do not
	conflict with our side are reflected in the merge result.
	For a binary file, the entire contents are taken from our side.
	+
	This should not be confused with the `ours` merge strategy, which does not
	even look at what the other tree contains at all. It discards everything
	the other tree did, declaring 'our' history contains all that happened in it.

	`theirs`;;
	This is the opposite of `ours`; note that, unlike `ours`, there is
	no `theirs` merge strategy to confuse this merge option with.

	`ignore-space-change`;;
	`ignore-all-space`;;
	`ignore-space-at-eol`;;
	`ignore-cr-at-eol`;;
	Treats lines with the indicated type of whitespace change as
	unchanged for the sake of a three-way merge. Whitespace
	changes mixed with other changes to a line are not ignored.
	See also linkgit:git-diff[1] `-b`, `-w`,
	`--ignore-space-at-eol`, and `--ignore-cr-at-eol`.
	+
	* If 'their' version only introduces whitespace changes to a line,
	'our' version is used;
	* If 'our' version introduces whitespace changes but 'their'
	version includes a substantial change, 'their' version is used;
	* Otherwise, the merge proceeds in the usual way.

	`renormalize`;;
	This runs a virtual check-out and check-in of all three stages
	of any file which needs a three-way merge. This option is
	meant to be used when merging branches with different clean
	filters or end-of-line normalization rules. See "Merging
	branches with differing checkin/checkout attributes" in
	linkgit:gitattributes[5] for details.

	`no-renormalize`;;
	Disables the `renormalize` option. This overrides the
	`merge.renormalize` configuration variable.

	`find-renames[=<n>]`;;
	Turn on rename detection, optionally setting the similarity
	threshold. This is the default. This overrides the
	`merge.renames` configuration variable.
	See also linkgit:git-diff[1] `--find-renames`.

	`rename-threshold=<n>`;;
	Deprecated synonym for `find-renames=<n>`.

	`no-renames`;;
	Turn off rename detection. This overrides the `merge.renames`
	configuration variable.
	See also linkgit:git-diff[1] `--no-renames`.

	`histogram`;;
	Deprecated synonym for `diff-algorithm=histogram`.

	`patience`;;
	Deprecated synonym for `diff-algorithm=patience`.

	`diff-algorithm=(histogram\|minimal\|myers\|patience)`;;
	Use a different diff algorithm while merging, which can help
	avoid mismerges that occur due to unimportant matching lines
	(such as braces from distinct functions). See also
	linkgit:git-diff[1] `--diff-algorithm`. Note that `ort`
	defaults to `diff-algorithm=histogram`, while regular diffs
	currently default to the `diff.algorithm` config setting.

	`subtree[=<path>]`;;
	This option is a more advanced form of 'subtree' strategy, where
	the strategy makes a guess on how two trees must be shifted to
	match with each other when merging. Instead, the specified path
	is prefixed (or stripped from the beginning) to make the shape of
	two trees to match.

	`recursive`::
	This is now a synonym for `ort`. It was an alternative
	implementation until v2.49.0, but was redirected to mean `ort`
	in v2.50.0. The previous recursive strategy was the default
	strategy for resolving two heads from Git v0.99.9k until
	v2.33.0.

	`resolve`::
	This can only resolve two heads (i.e. the current branch
	and another branch you pulled from) using a 3-way merge
	algorithm. It tries to carefully detect criss-cross
	merge ambiguities. It does not handle renames.

	`octopus`::
	This resolves cases with more than two heads, but refuses to do
	a complex merge that needs manual resolution. It is
	primarily meant to be used for bundling topic branch
	heads together. This is the default merge strategy when
	pulling or merging more than one branch.

	`ours`::
	This resolves any number of heads, but the resulting tree of the
	merge is always that of the current branch head, effectively
	ignoring all changes from all other branches. It is meant to
	be used to supersede old development history of side
	branches. Note that this is different from the `-Xours` option to
	the `ort` merge strategy.

	`subtree`::
	This is a modified `ort` strategy. When merging trees A and
	B, if B corresponds to a subtree of A, B is first adjusted to
	match the tree structure of A, instead of reading the trees at
	the same level. This adjustment is also done to the common
	ancestor tree.

	With the strategies that use 3-way merge (including the default, `ort`),
	if a change is made on both branches, but later reverted on one of the
	branches, that change will be present in the merged result; some people find
	this behavior confusing. It occurs because only the heads and the merge base
	are considered when performing a merge, not the individual commits. The merge
	algorithm therefore considers the reverted change as no change at all, and
	substitutes the changed version instead.