Re: cherry-pick very slow on big repository

From: Derrick Stolee <stolee@gmail.com>
Date: Nov 10, 2017, 12:59 UTC
Message-ID: <7e242038-50e5-2cfc-e810-401af78b8cdc@gmail.com>
In-Reply-To: <alpine.DEB.2.00.1711101333030.2391@ds9.cixit.se>

On 11/10/2017 7:37 AM, Peter Krefting wrote:

Show 23 quoted lines

> Jeff King:
>
>> Can you get a backtrace? I'd do something like:
>
> Seems that it spends most time in diffcore_count_changes(), that is 
> where it hits whenever I hit Ctrl+C (various line numbers 199-207 in 
> diffcore-delta.c; this is on the v2.15.0 tag).
>
> (gdb) bt
> #0  diffcore_count_changes (src=src@entry=0x55555db99970,
>     dst=dst@entry=0x55555d6a4810,
>     src_count_p=src_count_p@entry=0x55555db99998,
>     dst_count_p=dst_count_p@entry=0x55555d6a4838,
>     src_copied=src_copied@entry=0x7fffffffd3e0,
>     literal_added=literal_added@entry=0x7fffffffd3f0)
>     at diffcore-delta.c:203
> #1  0x00005555556dee1a in estimate_similarity (minimum_score=30000,
>     dst=0x55555d6a4810, src=0x55555db99970) at diffcore-rename.c:193
> #2  diffcore_rename (options=options@entry=0x7fffffffd4f0)
>     at diffcore-rename.c:560
> #3  0x0000555555623d83 in diffcore_std (
>     options=options@entry=0x7fffffffd4f0) at diff.c:5846
> ...

Git is spending time detecting renames, which implies you probably renamed a folder or added and deleted a large number of files. This rename detection is quadratic (# adds times # deletes).

You can remove this rename detection by running your cherry-pick with `git -c diff.renameLimit=1 cherry-pick ...`

See https://git-scm.com/docs/diff-config#diff-config-diffrenameLimit

Thanks, -Stolee