Git diff algorithm

[Balázs Bayer]

Hi all,

which diff algorithm is used by Gerrit by default, where can I change it, and if possible, which algorithms can be selected?

The documentation mentions the JGIT related config here: :https://gerrit-review.googlesource.com/Documentation/config-gerrit.html#jgitConfig

But it does not go into the details.

Gerrit version: 2.16.3

Thanks in advance,

Balázs

[Balázs Bayer]

and also: can we set this up on project level?

[Matthias Sohn]

see https://git-scm.com/docs/git-config#Documentation/git-config.txt-diffalgorithm for the configuration option "diff.algorithm"

JGit supports the algorithms "myers" and "histogram" and uses "histogram" as the default since it's faster and typically

creates nicer diffs for real world source files [1].

[1] https://git.eclipse.org/r/#/c/1721/

-Matthias

[David Ostrovsky]

Am Donnerstag, 24. Oktober 2019 14:07:01 UTC+2 schrieb Matthias Sohn:

On Thu, Oct 24, 2019 at 10:25 AM Balázs Bayer <balaz...@gmail.com> wrote:

Hi all,

which diff algorithm is used by Gerrit by default, where can I change it, and if possible, which algorithms can be selected?

The documentation mentions the JGIT related config here: :https://gerrit-review.googlesource.com/Documentation/config-gerrit.html#jgitConfig

But it does not go into the details.

Gerrit version: 2.16.3

see https://git-scm.com/docs/git-config#Documentation/git-config.txt-diffalgorithm for the configuration option "diff.algorithm"

JGit supports the algorithms "myers" and "histogram" and uses "histogram" as the default since it's faster and typically

creates nicer diffs for real world source files [1].

We have also seen issues with Myers diff implementation in the wild. That why the code

is somehow convoluted, and starts diffing with whatever algorithm is configured on JGit

side, but then interrupts the computation after configurable timeout (default 5 seconds),

and re-computes the diff with hard coded histogram diff algorithm, see: [2].

[2] https://github.com/GerritCodeReview/gerrit/blob/master/java/com/google/gerrit/server/patch/PatchListLoader.java#L435-L461