Re: [PATCH 1/3] doc: clarify documentation for rename/copy limits

From: Derrick Stolee <stolee@gmail.com>
Date: Jul 12, 2021, 15:03 UTC
Message-ID: <c25e29a9-3a15-4079-43fd-b77746927b16@gmail.com>
In-Reply-To: <7dc448df6ec6edb41464a4115017064cf41b2d83.1625964399.git.gitgitgadget@gmail.com>

On 7/10/2021 8:46 PM, Elijah Newren via GitGitGadget wrote:

> From: Elijah Newren <newren@gmail.com>

...

Show 8 quoted lines

>  diff.renameLimit::
> -	The number of files to consider when performing the copy/rename
> -	detection; equivalent to the 'git diff' option `-l`. This setting
> -	has no effect if rename detection is turned off.
> +	The number of files to consider in the quadratic portion of
> +	copy/rename detection; equivalent to the 'git diff' option
> +	`-l`.  If not set, the default value is 400.  This setting has
> +	no effect if rename detection is turned off.

...

Show 11 quoted lines

>  merge.renameLimit::
> -	The number of files to consider when performing rename detection
> -	during a merge; if not specified, defaults to the value of
> -	diff.renameLimit. This setting has no effect if rename detection
> -	is turned off.
> +	The number of files to consider in the quadratic portion of
> +	rename detection during a merge.  If not specified, defaults
> +	to the value of diff.renameLimit.  If neither
> +	merge.renameLimit nor diff.renameLimit are specified, defaults
> +	to 1000.  This setting has no effect if rename detection is
> +	turned off.

...

Show 12 quoted lines

>  -l<num>::
> -	The `-M` and `-C` options require O(n^2) processing time where n
> -	is the number of potential rename/copy targets.  This
> -	option prevents rename/copy detection from running if
> -	the number of rename/copy targets exceeds the specified
> -	number.
> +	The `-M` and `-C` options can require O(n^2) processing time
> +	where n is the number of potential rename/copy targets.  This
> +	option prevents the quadratic portion of rename/copy detection
> +	from running if the number of rename/copy targets exceeds the
> +	specified number.  Defaults to diff.renameLimit, or if that is
> +	also unspecified, to 400.

These changes are clear to me, but I also know how a bit about how the rename algorithm works and what "the quadratic portion" means. I wonder if this is sufficient detail to help a user less versed in Git's internals.

Perhaps we should instead be describing the set of "potential inexact renames" as a more descriptive approach? Here is a possible way to use this wording instead:

  merge.renameLimit::
      The number of potential inexact renames to consider when
      performing rename detection during a merge; if this limit
      is exceeded, then no inexact renames are computed. Renames
      where the content does not change are excluded from this
      limit. If not specified, defaults to...

Feel free to take or leave any of this example.

Thanks, -Stolee