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Re: [PATCH] git-download: Speed up 'git-predicate'.

From: Christopher Baines
Subject: Re: [PATCH] git-download: Speed up 'git-predicate'.
Date: Wed, 7 Jun 2017 19:12:38 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 07/06/17 13:40, Ludovic Courtès wrote:
> Hi Christopher,
> Christopher Baines <address@hidden> skribis:
>> Running the current implementation of git-predicate on the guix
>> repository with 50 trials takes:
>>   real    0m5.374s
>>   user    0m4.052s
>>   sys     0m1.484s
>> Compared to the following for the patched implementation:
>>   real    0m8.398s
>>   user    0m5.040s
>>   sys     0m2.016s
>> This shows that the patched implementation has decreased the
>> performance. Using the real value, the test time has increased by ~3
>> seconds. This corresponds roughly to a change from ~0.11 seconds
>> previously, to ~0.17 seconds for each individual traversal of the entire
>> repository.
>> I encountered a performance issue when trying to use git-predicate with
>> this repository [2], which I have written a Guix package for here [3].
>> Instead of the 1463 files that git ls-files reports locally for the guix
>> repository, smart-answers contains 26732 files.
>> The running time with smart-answers is left as an exercise to the
>> reader, all I can say is that on my machine, it takes more than 40
>> minutes for just 1 trial.
>> Using this patch, running the test script with 1 trial gives:
>>   real    0m4.917s
>>   user    0m3.640s
>>   sys     0m1.428s
> So in short, the new implementation is 100 times faster on large repos
> but roughly the same or slightly slower on smaller repos, right?

Yep, that's right :)

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