Subject: Re: [PATCH v2] merge-ort: avoid assuming all renames detected

From: Junio C Hamano <[email-masked]>
Date: Mon, 17 Jan 2022 14:16:09 -0800

Elijah Newren <[email-masked]> writes:

> On Mon, Jan 17, 2022 at 11:33 AM Junio C Hamano <[email-masked]> wrote:
>>
>> "Elijah Newren via GitGitGadget" <[email-masked]> writes:
>>
>> > From: Elijah Newren <[email-masked]>
>> >
>> > In commit 8b09a900a1 ("merge-ort: restart merge with cached renames to
>> > reduce process entry cost", 2021-07-16), we noted that in the merge-ort
>> > steps of
>> >     collect_merge_info()
>> >     detect_and_process_renames()
>> >     process_entries()
>> > that process_entries() was expensive, and we could often make it cheaper
>> > by changing this to
>> >     collect_merge_info()
>> >     detect_and_process_renames()
>> >     <cache all the renames, and restart>
>> >     collect_merge_info()
>> >     detect_and_process_renames()
>> >     process_entries()
>> > because the second collect_merge_info() would be cheaper (we could avoid
>> > traversing into some directories), the second
>> > detect_and_process_renames() would be free since we had already detected
>> > all renames, and then process_entries() has far fewer entries to handle.
>> >
>> > However, this was built on the assumption that the first
>> > detect_and_process_renames() actually detected all potential renames.
>> > If someone has merge.renameLimit set to some small value, that
>> > assumption is violated which manifests later with the following message:
>> >
>> >     $ git -c merge.renameLimit=1 rebase upstream
>> >     ...
>> >     git: merge-ort.c:546: clear_or_reinit_internal_opts: Assertion
>> >     `renames->cached_pairs_valid_side == 0' failed.
>> >
>> > Turn off this cache-renames-and-restart whenever we cannot detect all
>> > renames, and add a testcase that would have caught this problem.
>> >
>> > Reported-by: Taylor Blau <[email-masked]>
>> > Signed-off-by: Elijah Newren <[email-masked]>
>> > ---
>>
>> Thanks.  An Ack?
>
> Taylor told me the code change fixed his case, and that he'd review my
> full patch with the testcase when I posted it.  Let's wait to hear
> from him.

Yes, I am waiting (notice who is on To: and not Cc: on the message
you are responding to ;-).

Thanks.