> -----Original Message----- > From: Ben Peart [mailto:peart...@gmail.com] > Sent: Thursday, May 18, 2017 12:58 PM > To: Junio C Hamano <gits...@pobox.com>; David Turner > <david.tur...@twosigma.com> > Cc: 'Christian Couder' <christian.cou...@gmail.com>; Johannes Schindelin > <johannes.schinde...@gmx.de>; git <git@vger.kernel.org>; Nguyễn Thái Ngọc > Duy <pclo...@gmail.com>; Ben Peart <benpe...@microsoft.com> > Subject: Re: [PATCH 0/1] Preserve the untracked cache across checkout, reset > -- > hard, etc > > > > On 5/9/2017 8:51 AM, Ben Peart wrote: > > > > On 5/9/2017 1:02 AM, Junio C Hamano wrote: > >> David Turner <david.tur...@twosigma.com> writes: > >> > >>> Can you actually keep the email address as my Twopensource one? I > >>> want to make sure that Twitter, my employer at the time, gets credit > >>> for this work (just as I want to make sure that my current employer, > >>> Two Sigma, gets credit for my current work). > >>> > >>> Please feel free to add Signed-off-by: David Turner > >>> <dtur...@twosigma.com> in case that makes tracking easier. > >>> > >>> Thanks. > >>> > >>> WRT the actual patch, I want to note that past me did not do a great > >>> job here. The tests do not correctly check that the post-checkout > >>> untracked cache is still valid after a checkout. > >>> For example, let's say that previously, the directory foo was > >>> entirely untracked (but it contained a file bar), but after the > >>> checkout, there is a file foo/baz. Does the untracked cache need to > >>> get updated? > >>> > >>> Unfortunately, the untracked cache is very unlikely to make it to > >>> the top of my priority list any time soon, so I won't be able to > >>> correct this test (and, if necessary, correct the code). But I > >>> would strongly suggest that the test be improved before this code is > >>> merged. > >>> > >>> Thanks for CCing me. > >> I will try to find time to tweak what was sent to the list here to > >> reflect your affiliations better, but marked with DONTMERGE waiting > >> for the necessary updates you mentioned above, so that this change is > >> not forgotten. It may turn out to be that copying from src to dst > >> like the patch does is all that is needed, or the cache may need > >> further invalidation when the copying happens, and I haven't got a > >> good feeling that anybody who are familiar with the codepath vetted > >> the correctness from seeing the discussion from sidelines (yet). > >> > >> Thanks. > > > > I've been looking into similar issues with the cache associated with > > using a file system monitor (aka Watchman) > > (https://github.com/git-for-windows/git/compare/master...benpeart:fsmo > > nitor) to speed updating the index to reflect changes in the working > > directory. > > > > I can take a look and see if this patch results in valid results and > > reply to the thread or resubmit as needed. > > > > Ben > > TLDR: the patch looks good from my perspective but I'd like the experts to > weigh > in as well.
Thanks for looking into this. I'm glad to learn that I got it right the first time, although I still wish I had been more assiduous about testing back then. > After digging into the untracked cache code and thinking about whether it is > reasonable to copy the cache from the old index to the new index in > unpack_trees() I believe the answer is "yes." I'm not the expert in this > code so I'll > outline my reasoning here and hopefully the real experts can review it and > see if > I've missed something. > > The interesting part of the untracked cache for this discussion is the list of > untracked_cache_dir structures. Because each directory cache entry contains > stat_data (esp ctime and mtime) for that directory - the existing logic will > detect > if that directory has had any changes made in it since the cache entry was > saved. > It doesn't really care when, why, or how the change was made, just if one has > happened. > > I then tried to think of ways that this logic could be broken (like David's > example > above) but was unsuccessful in coming up with any. This makes sense because > the untracked cache obviously has to correctly detect _any_ change so really > doesn't care whether it's cached state was initially saved before or after a > call to > unpack_trees(). It looks like unpack_trees calls (somewhere -- I didn't investigate the full call chain) untracked_cache_invalidate_entry. It looks like my patch adds the move *after* any invalidation, though, so I think this is OK. > Even scenarios of creating files in sub-directories of sub-directories works > because eventually, either is a directory or file is created in a cached > directory > entry which will change the mtime of that directory and invalidate that part > of > the cache. > > Ultimately, it is this behavior of saving the mtime of each cached directory > that > makes this all work as each entry can be validated/invalidated separately from > all the rest and independently from the index from which they came. > > > Once I did the code examination and thinking exercise, I wanted to test it out > and see if the theory held up. I started out with some manual testing (esp > of the > scenario David mentioned) and then wrote a couple of additional tests all of > which passed. > > I then ran all existing git tests with the patch applied and they all passed. > This > only really tells us that it didn't break anything because untracked cache is > turned off by default but it does show us that it still passes the untracked > cache > specific test cases (as they obviously turn it on). > > I then modified the test_create_repo() function in test-lib-functions.sh to > turn > on the untracked cache feature after creating the test repo and ran all the > tests > again twice - the first time without the patch and again with the patch). > This run > is more interesting because it is testing that having the untracked cache > turned > (with and without the > patch) on doesn't break anything. > > There were two test scripts that had failures: > > t7063-status-untracked-cache.sh failed the test "not ok 1 - > core.untrackedCache > is unset" This is actually a positive result because it is showing that I > successfully > turned on the untracked cache feature. > > t1700-split-index.sh failed several tests in both runs (with and without > patch) and upon examining the tests and their failures they are to be expected > and do not indicate any bug. Specifically, the failures were caused because > the > tests check the sha of the index against a hard coded value in the test > script. > Because the untracked cache is turned on, the sha of the index does not match > that hard coded value. I edited several of the tests to update the sha they > are > checking against to match the sha actually generated and the tests pass. > > In the end, both my code examination and all the testing I was able to do give > me some confidence that the patch will produce valid results. > However, I'm not the expert in this area so I'd like the experts to weigh in > on any > potential issues this patch may cause that I've missed. This testing seems sufficient to me, assuming that the new automated tests make it into the patch. Thanks for finishing this up -- it had slipped my mind entirely.
