From: Derrick Stolee <stolee@gmail.com>
To: Elijah Newren <newren@gmail.com>
Cc: Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>,
Git Mailing List <git@vger.kernel.org>,
Derrick Stolee <dstolee@microsoft.com>,
Jonathan Tan <jonathantanmy@google.com>,
Taylor Blau <me@ttaylorr.com>, Junio C Hamano <gitster@pobox.com>,
Jeff King <peff@peff.net>
Subject: Re: [PATCH 3/3] diffcore-rename: guide inexact rename detection based on basenames
Date: Mon, 8 Feb 2021 06:31:13 -0500 [thread overview]
Message-ID: <b4eeb6a1-a801-e984-d245-f291a0cf9727@gmail.com> (raw)
In-Reply-To: <CABPp-BHPgUHFFzTd7suhqj=zEXQ61vxKU6X9gZvow5a=TLg3iw@mail.gmail.com>
On 2/8/2021 3:27 AM, Elijah Newren wrote:
> Hi,
>
> On Sun, Feb 7, 2021 at 6:38 AM Derrick Stolee <stolee@gmail.com> wrote:
>>
>> On 2/6/21 5:52 PM, Elijah Newren via GitGitGadget wrote:
>>> From: Elijah Newren <newren@gmail.com>
>>>
>>> Make use of the new find_basename_matches() function added in the last
>>> two patches, to find renames more rapidly in cases where we can match up
>>> files based on basenames.
>>
>> This is a valuable heuristic.
>>
>>> For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
>>> performance work; instrument with trace2_region_* calls", 2020-10-28),
>>> this change improves the performance as follows:
>>>
>>> Before After
>>> no-renames: 13.815 s ± 0.062 s 13.138 s ± 0.086 s
>>> mega-renames: 1799.937 s ± 0.493 s 169.488 s ± 0.494 s
>>> just-one-mega: 51.289 s ± 0.019 s 5.061 s ± 0.017 s
>>
>> These numbers are very impressive.
>>
>> Before I get too deep into reviewing these patches, I do want
>> to make it clear that the speed-up is coming at the cost of
>> a behavior change. We are restricting the "best match" search
>> to be first among files with common base name (although maybe
>> I would use 'suffix'?). If we search for a rename among all
>> additions and deletions ending the ".txt" we might find a
>> similarity match that is 60% and declare that a rename, even
>> if there is a ".txt" -> ".md" pair that has a 70% match.
>
> I'm glad you all are open to possible behavioral changes, but I was
> proposing a much smaller behavioral change that is quite different
> than what you have suggested here. Perhaps my wording was poor; I
> apologize for forgetting that "basename" has different meanings in
> different contexts. Let me try again; I am not treating the filename
> extension as special in any manner here; by "basename" I just mean the
> portion of the path ignoring any leading directories. Thus
> src/foo.txt
> might be a good match against
> source/foo.txt
> but this optimization as a preliminary step would not consider
> matching src/foo.txt against any of
> source/bar.txt
> source/foo.md
> since the basenames ('bar.txt' and 'foo.md') do not match our original
> file's basename ('foo.txt').
>
> Of course, if this preliminary optimization step fails to find another
> "foo.txt" to match src/foo.txt against (or finds more than one and
> thus doesn't compare against any of them), then the fallback inexact
> rename detection matrix might match it against either of those two
> latter paths, as it always has.
Thank you for making it clear that I had misunderstood what the
optimization is actually doing. A much more narrow scope makes
more sense, and avoids the quadratic problem even when many files
of the same suffix are renamed.
>> This could be documented in a test case, to demonstrate that
>> we are making this choice explicitly.
My test is thus bogus, but you could have a similar one for
your actual optimization.
>> So, in this way, we are changing the optimization function
>> that is used to determine the "best" rename available. It
>> might be good to update documentation for how we choose
>> renames:
>
> Seems reasonable; I'll add some commentary below on the rules...
Your commentary is helpful. I look forward to reading your
carefully-written docs in the next version ;).
>> i. among files with the same basename (trailer
>> after final '.') select pairs with highest
>> similarity.
>
> This is an interesting idea, but is not what I implemented.
That's what I get for reading the commit messages quickly and
commenting on what I _think_ is going on instead of actually
reading the code carefully. Sorry about that.
> It is
> possible that your suggestion is also a useful optimization; it'd be
> hard to know without trying. However, as noted in optimization batch
> 8 that I'll be submitting later, I'm worried about having any
> optimization pre-steps doing more than O(1) comparisons per path (and
> here you suggest comparing each .txt file with all other .txt files);
> doing that can interact badly with optimization batch 9.
> Additionally, unless we do something to avoid re-comparing files again
> when doing the later all-unmatched-files-against-each-other check,
> then worst case behavior can approach twice as slow as the original
> code.
Right. If Git decides to reorganize all of its *.c files in one
commit, we would still get quadratic behavior in rename detection.
Maybe it's not _that_ much of an improvement.
Thanks,
-Stolee
next prev parent reply other threads:[~2021-02-08 11:35 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-06 22:52 [PATCH 0/3] Optimization batch 7: use file basenames to guide rename detection Elijah Newren via GitGitGadget
2021-02-06 22:52 ` [PATCH 1/3] diffcore-rename: compute basenames of all source and dest candidates Elijah Newren via GitGitGadget
2021-02-06 22:52 ` [PATCH 2/3] diffcore-rename: complete find_basename_matches() Elijah Newren via GitGitGadget
2021-02-06 22:52 ` [PATCH 3/3] diffcore-rename: guide inexact rename detection based on basenames Elijah Newren via GitGitGadget
2021-02-07 14:38 ` Derrick Stolee
2021-02-07 19:51 ` Junio C Hamano
2021-02-08 8:38 ` Elijah Newren
2021-02-08 11:43 ` Derrick Stolee
2021-02-08 16:25 ` Elijah Newren
2021-02-08 17:37 ` Junio C Hamano
2021-02-08 22:00 ` Elijah Newren
2021-02-08 23:43 ` Junio C Hamano
2021-02-08 23:52 ` Elijah Newren
2021-02-08 8:27 ` Elijah Newren
2021-02-08 11:31 ` Derrick Stolee [this message]
2021-02-08 16:09 ` Elijah Newren
2021-02-07 5:19 ` [PATCH 0/3] Optimization batch 7: use file basenames to guide rename detection Junio C Hamano
2021-02-07 6:05 ` Elijah Newren
2021-02-09 11:32 ` [PATCH v2 0/4] " Elijah Newren via GitGitGadget
2021-02-09 11:32 ` [PATCH v2 1/4] diffcore-rename: compute basenames of all source and dest candidates Elijah Newren via GitGitGadget
2021-02-09 13:17 ` Derrick Stolee
2021-02-09 16:56 ` Elijah Newren
2021-02-09 17:02 ` Derrick Stolee
2021-02-09 17:42 ` Elijah Newren
2021-02-09 11:32 ` [PATCH v2 2/4] diffcore-rename: complete find_basename_matches() Elijah Newren via GitGitGadget
2021-02-09 13:25 ` Derrick Stolee
2021-02-09 17:17 ` Elijah Newren
2021-02-09 17:34 ` Derrick Stolee
2021-02-09 11:32 ` [PATCH v2 3/4] diffcore-rename: guide inexact rename detection based on basenames Elijah Newren via GitGitGadget
2021-02-09 13:33 ` Derrick Stolee
2021-02-09 17:41 ` Elijah Newren
2021-02-09 18:59 ` Junio C Hamano
2021-02-09 11:32 ` [PATCH v2 4/4] gitdiffcore doc: mention new preliminary step for rename detection Elijah Newren via GitGitGadget
2021-02-09 12:59 ` Derrick Stolee
2021-02-09 17:03 ` Junio C Hamano
2021-02-09 17:44 ` Elijah Newren
2021-02-10 15:15 ` [PATCH v3 0/5] Optimization batch 7: use file basenames to guide " Elijah Newren via GitGitGadget
2021-02-10 15:15 ` [PATCH v3 1/5] t4001: add a test comparing basename similarity and content similarity Elijah Newren via GitGitGadget
2021-02-13 1:15 ` Junio C Hamano
2021-02-13 4:50 ` Elijah Newren
2021-02-13 23:56 ` Junio C Hamano
2021-02-14 1:24 ` Elijah Newren
2021-02-14 1:32 ` Junio C Hamano
2021-02-14 3:14 ` Elijah Newren
2021-02-10 15:15 ` [PATCH v3 2/5] diffcore-rename: compute basenames of all source and dest candidates Elijah Newren via GitGitGadget
2021-02-13 1:32 ` Junio C Hamano
2021-02-10 15:15 ` [PATCH v3 3/5] diffcore-rename: complete find_basename_matches() Elijah Newren via GitGitGadget
2021-02-13 1:48 ` Junio C Hamano
2021-02-13 18:34 ` Elijah Newren
2021-02-13 23:55 ` Junio C Hamano
2021-02-14 3:08 ` Elijah Newren
2021-02-10 15:15 ` [PATCH v3 4/5] diffcore-rename: guide inexact rename detection based on basenames Elijah Newren via GitGitGadget
2021-02-13 1:49 ` Junio C Hamano
2021-02-10 15:15 ` [PATCH v3 5/5] gitdiffcore doc: mention new preliminary step for rename detection Elijah Newren via GitGitGadget
2021-02-10 16:41 ` Junio C Hamano
2021-02-10 17:20 ` Elijah Newren
2021-02-11 8:15 ` [PATCH v4 0/6] Optimization batch 7: use file basenames to guide " Elijah Newren via GitGitGadget
2021-02-11 8:15 ` [PATCH v4 1/6] t4001: add a test comparing basename similarity and content similarity Elijah Newren via GitGitGadget
2021-02-11 8:15 ` [PATCH v4 2/6] diffcore-rename: compute basenames of all source and dest candidates Elijah Newren via GitGitGadget
2021-02-11 8:15 ` [PATCH v4 3/6] diffcore-rename: complete find_basename_matches() Elijah Newren via GitGitGadget
2021-02-11 8:15 ` [PATCH v4 4/6] diffcore-rename: guide inexact rename detection based on basenames Elijah Newren via GitGitGadget
2021-02-11 8:15 ` [PATCH v4 5/6] gitdiffcore doc: mention new preliminary step for rename detection Elijah Newren via GitGitGadget
2021-02-11 8:15 ` [PATCH v4 6/6] merge-ort: call diffcore_rename() directly Elijah Newren via GitGitGadget
2021-02-13 1:53 ` [PATCH v4 0/6] Optimization batch 7: use file basenames to guide rename detection Junio C Hamano
2021-02-14 7:51 ` [PATCH v5 " Elijah Newren via GitGitGadget
2021-02-14 7:51 ` [PATCH v5 1/6] t4001: add a test comparing basename similarity and content similarity Elijah Newren via GitGitGadget
2021-02-14 7:51 ` [PATCH v5 2/6] diffcore-rename: compute basenames of source and dest candidates Elijah Newren via GitGitGadget
2021-02-14 7:51 ` [PATCH v5 3/6] diffcore-rename: complete find_basename_matches() Elijah Newren via GitGitGadget
2021-02-14 7:51 ` [PATCH v5 4/6] diffcore-rename: guide inexact rename detection based on basenames Elijah Newren via GitGitGadget
2021-02-14 7:51 ` [PATCH v5 5/6] gitdiffcore doc: mention new preliminary step for rename detection Elijah Newren via GitGitGadget
2021-02-14 7:51 ` [PATCH v5 6/6] merge-ort: call diffcore_rename() directly Elijah Newren via GitGitGadget
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