Re: Should update-index --refresh force writing the index in case of racy timestamps?

From: Marc Strapetz <marc.strapetz@syntevo.com>
Date: Dec 22, 2021, 11:42 UTC
Message-ID: <5a74b0bc-d713-e8bf-5952-dbaaf5d886e7@syntevo.com>
In-Reply-To: <xmqqee6a22rj.fsf@gitster.g>

On 18/12/2021 01:08, Junio C Hamano wrote:

Show 23 quoted lines

> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
> 
>> On 2021-12-17 at 10:44:32, Marc Strapetz wrote:
>>> For one of my Git-LFS test repositories, switching between branches quite
>>> often results in lots of racy index timestamps. Subsequent calls to "git
>>> update-index --refresh" or "git status" will invoke the "lfs" filter over
>>> and over again, just to figure out that all entries are still up-to-date.
>>> Hence, the index will never be rewritten and racy timestamps will remain.
>>>
>>> To break out of this state, it seems favorable to write the index if any
>>> racy timestamp is detected. We will be able to provide a patch if this
>>> change sounds reasonable.
>>
>> Sure, this sounds reasonable, especially if, as you mentioned, git
>> status already does this.  We might as well make the plumbing commands
>> as functional as the porcelain commands.
> 
> Given that "update-index --refresh" is a way to say "we know
> something changed to make cached stat information dirty even for
> otherwise clean paths and we want our 'diff-files' and other
> plumbing command to start relying on the cached stat information
> again, so please do as much I/O as you need", I agree that it should
> do as thourough job as necessary.

Thanks! I have now submitted a pull request via gitgitgadget.

I had some problems to understand what the correct place to set active_cache_changed is and have decided to keep it as close as possible to refresh_cache(): unresolve_callback() and reupdate_callback() may reset active_cache_changed in case of errors. On the other hand, active_cache_changed may be set again later for a preferred_index_format change and for read_from_stdin (as part of update_one()), so in the end the callbacks may be overruled and the index may finally be written. I'm not sure whether these combinations can actually occur and whether this might cause any troubles. I just wanted to point out.

-Marc