Re: [PATCH v1] dir.c: don't flag the index as dirty for changes to the untracked cache

From: Ben Peart <peartben@gmail.com>
Date: Feb 6, 2018, 01:39 UTC
Message-ID: <6ff2ecb4-7e37-3b06-3722-cccec2329934@gmail.com>
In-Reply-To: <xmqqd11j9mx2.fsf@gitster-ct.c.googlers.com>

On 2/5/2018 3:55 PM, Junio C Hamano wrote:

Show 32 quoted lines

> Ben Peart <benpeart@microsoft.com> writes:
> 
>> The untracked cache saves its current state in the UNTR index extension.
>> Currently, _any_ change to that state causes the index to be flagged as dirty
>> and written out to disk.  Unfortunately, the cost to write out the index can
>> exceed the savings gained by using the untracked cache.  Since it is a cache
>> that can be updated from the current state of the working directory, there is
>> no functional requirement that the index be written out for every change to the
>> untracked cache.
>>
>> Update the untracked cache logic so that it no longer forces the index to be
>> written to disk except in the case where the extension is being turned on or
>> off.  When some other git command requires the index to be written to disk, the
>> untracked cache will take advantage of that to save it's updated state as well.
>> This results in a performance win when looked at over common sequences of git
>> commands (ie such as a status followed by add, commit, etc).
>>
>> After this patch, all the logic to track statistics for the untracked cache
>> could be removed as it is only used by debug tracing used to debug the untracked
>> cache.
>>
>> Signed-off-by: Ben Peart <benpeart@microsoft.com>
>> ---
>>
> 
> OK, so in other words (note: not a suggestion to use different
> wording in the log message; just making sure I got the motivation
> behind this change correctly), without this new environment
> variable, changes to untracked cache alone (due to observed changes
> in the filesystem) does not count as "in-core index changed so we
> need to write it back to the disk".
>

Correct

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> That makes sense to me.
> 
> Is it envisioned that we want to have similar but different "testing
> only" behaviour around this area?  If not, this environment variable
> sounds more like "force-flush untracked cache", not "test untracked
> cache", to me.
>

Many of the tests make a change and then verify that the on disk structure was updated correctly. This was the simplest way to keep those tests functioning. I don't imagine this would be used for anything other than enabling the tests. I hate naming so am happy to name it which ever you think is best. :)

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>> +GIT_TEST_UNTRACKED_CACHE=true
>> +export GIT_TEST_UNTRACKED_CACHE
>> +
>>   sync_mtime () {
>>   	find . -type d -ls >/dev/null
>>   }
>>
>> base-commit: 5be1f00a9a701532232f57958efab4be8c959a29