Elijah Newren wrote:
> On Fri, Oct 29, 2021 at 6:56 AM Victoria Dye via GitGitGadget
> <gitgitgadget@xxxxxxxxx> wrote:
>>
>> From: Victoria Dye <vdye@xxxxxxxxxx>
>>
>> If `command_requires_full_index` is false, ensure correct in-core index
>> sparsity on read by calling `ensure_correct_sparsity`. This change is meant
>> to update the how the index is read in a command after sparse index-related
>
> s/update the how/update how/ ?
>
This was probably the result of mixing up "update the way" and "update how".
I'll go with the latter.
>> repository settings are modified. Previously, for example, if `index.sparse`
>> were changed from `true` to `false`, the in-core index on the next command
>> would be sparse. The index would only be expanded to full when it was next
>> written to disk.
>>
>> By adding a call to `ensure_correct_sparsity`, the in-core index now matches
>> the sparsity dictated by the relevant repository settings as soon as it is
>> read into memory, rather than when it is later written to disk.
>
> I split up reading this series across different days, and when I got
> here, my first reaction was "Okay, but why would you want that?
> Sounds like extra work for no gain." I went and looked up the cover
> letter and saw you mentioned that this "introduces the ability to
> enable/disable the sparse index on a command-by-command basis (e.g.,
> allowing a user to troubleshoot a sparse-aware command with '-c
> index.sparse=false' [1]). That seems like a good reason to me, and
> sounds like it belongs in this commit message. But it sounds like you
> had other reasons in mind. If so, could you share them; I'm having
> difficulty understanding how this would make a difference other than
> in the troubleshooting scenario.
>
The troubleshooting scenario was what inspired this change in the first
place, but it applies any time someone changes repository settings outside
of `git sparse-checkout init`. One relevant scenario I can imagine is if a
user enables `index.sparse, commands would not use the sparse index until a
command that *writes* the index is executed:
$ git config index.sparse true
$ git diff # read full index, full in-core, no write
$ git add . # read full index, full in-core, write sparse
$ git diff # read sparse index, sparse in-core, no write
Another scenario might be enabling `index.sparse`, then running a command
that turns out to be surprisingly slow because it's operating on a full
index in-core (i.e., much slower than the convert_to_sparse + command with
sparse index would be).
These are definitely edge cases - they rely on manual config changes, and
they're only really noticeable 1) if the config change is immediately
followed by index read-only commands and 2) if the first index-writing
command after the config change is slow. That said, on the off chance that a
user (or future developer) encounter one of these scenarios, I think it'll
be helpful to have `index.sparse` take effect "immediately" after the config
change.
I'll include these (and the troubleshooting) examples in the updated commit
message.
>>
>> Helped-by: Junio C Hamano <gitster@xxxxxxxxx>
>> Co-authored-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
>> Signed-off-by: Victoria Dye <vdye@xxxxxxxxxx>
>> ---
>> read-cache.c | 8 ++++++
>> t/t1092-sparse-checkout-compatibility.sh | 31 ++++++++++++++++++++++++
>> 2 files changed, 39 insertions(+)
>>
>> diff --git a/read-cache.c b/read-cache.c
>> index a78b88a41bf..b3772ba70a1 100644
>> --- a/read-cache.c
>> +++ b/read-cache.c
>> @@ -2337,9 +2337,17 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
>>
>> if (!istate->repo)
>> istate->repo = the_repository;
>> +
>> + /*
>> + * If the command explicitly requires a full index, force it
>> + * to be full. Otherwise, correct the sparsity based on repository
>> + * settings and other properties of the index (if necessary).
>> + */
>> prepare_repo_settings(istate->repo);
>> if (istate->repo->settings.command_requires_full_index)
>> ensure_full_index(istate);
>> + else
>> + ensure_correct_sparsity(istate);
>>
>> return istate->cache_nr;
>>
>> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
>> index ca91c6a67f8..59accde1fa3 100755
>> --- a/t/t1092-sparse-checkout-compatibility.sh
>> +++ b/t/t1092-sparse-checkout-compatibility.sh
>> @@ -694,6 +694,37 @@ test_expect_success 'sparse-index is expanded and converted back' '
>> test_region index ensure_full_index trace2.txt
>> '
>>
>> +test_expect_success 'index.sparse disabled inline uses full index' '
>> + init_repos &&
>> +
>> + # When index.sparse is disabled inline with `git status`, the
>> + # index is expanded at the beginning of the execution then never
>> + # converted back to sparse. It is then written to disk as a full index.
>> + rm -f trace2.txt &&
>> + GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
>> + git -C sparse-index -c index.sparse=false status &&
>> + ! test_region index convert_to_sparse trace2.txt &&
>> + test_region index ensure_full_index trace2.txt &&
>> +
>> + # Since index.sparse is set to true at a repo level, the index
>> + # is converted from full to sparse when read, then never expanded
>> + # over the course of `git status`. It is written to disk as a sparse
>> + # index.
>> + rm -f trace2.txt &&
>> + GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
>> + git -C sparse-index status &&
>> + test_region index convert_to_sparse trace2.txt &&
>> + ! test_region index ensure_full_index trace2.txt &&
>> +
>> + # Now that the index has been written to disk as sparse, it is not
>> + # converted to sparse (or expanded to full) when read by `git status`.
>> + rm -f trace2.txt &&
>> + GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
>> + git -C sparse-index status &&
>> + ! test_region index convert_to_sparse trace2.txt &&
>> + ! test_region index ensure_full_index trace2.txt
>> +'
>> +
>> ensure_not_expanded () {
>> rm -f trace2.txt &&
>> echo >>sparse-index/untracked.txt &&
>> --
>> gitgitgadget
>
> The rest of the patch looks fine.
>
