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Re: cherry-pick very slow on big repository

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