[swift-dev] Very slow Set<String>(arrayOfStrings) for some arrayOfStrings

[Arnold Schwaighofer]

That is the difference between a “String” type instance that can use the ascii fast path and NSString backed “String” type instances.

When the code translates the string (the map function that calls upper case) it becomes a natively backed “String” that isASCII.

// The strings in strings.txt are not strange in any way, they all match ^[a-zA-Z ]+$.

Set the isASCII bit and things are blazing fast.

The other path is that componentsSeparatedByString(separator: String) -> [String] returns an “[String]” where every “String” is backed by “NSString”. When it comes to do comparison we call a NSString function on the NSString and this is where the difference in performance comes from.




> On Mar 2, 2016, at 12:15 AM, Jens Persson via swift-dev <swift-dev at swift.org> wrote:
> 
> I guess it would be possible to isolate the problem by analyzing my example, and thereby making it possible to write a smaller benchmark which doesn't need that big textfile. I didn't manage to do that however, hence my question about the problem here.
> /Jens
> 
> On Wed, Mar 2, 2016 at 9:11 AM, Jens Persson <jens at bitcycle.com> wrote:
> Thanks, but I'll have to invite anyone with more time and experience to do that.
> 
> One (of many) thing(s) I wouldn't know how include/handle is the 1.3 MB text file for the particular arrayOfStrings that makes Set(arrayOfStrings) slow. It seems a bit unnecessary/bloating to put it in the code base.
> 
> /Jens
> 
> On Tue, Mar 1, 2016 at 11:58 PM, Nadav Rotem <nrotem at apple.com> wrote:
> Hi Jens,
> 
> Thanks for reporting this issue. I don’t know what’s going on but we’ll take a look. 
> 
> I think it would be great if you could add this program as a benchmark under swift/benchmarks/.  This will allow us to track the performance of this test and ensure that we don’t regress. 
> 
> Thanks,
> Nadav 
> 
>> On Mar 1, 2016, at 5:01 AM, Jens Persson via swift-dev <swift-dev at swift.org> wrote:
>> 
>> For some particular arrays of strings, creating a Set<String>(arrayOfStrings) takes about 100 to 200 times longer than for other very similar arrays of strings (equally many unique simple [a-zA-Z ]+ strings).
>> 
>> I've put together a tiny program to demonstrate the problem here:
>> http://sloppyfocus.com/slowSetFromParticularButSeeminglyNormalArrayOfStrings.html
>> 
>> Is this due to a bug / performance problem in Set or can it be explained (and solved) in some way?
>> 
>> /Jens
>> 
>> _______________________________________________
>> swift-dev mailing list
>> swift-dev at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-dev
> 
> 
> 
> 
> -- 
> bitCycle AB | Smedjegatan 12 | 742 32 Östhammar | Sweden
> http://www.bitcycle.com/
> Phone: +46-73-753 24 62
> E-mail: jens at bitcycle.com
> 
> 
> 
> 
> -- 
> bitCycle AB | Smedjegatan 12 | 742 32 Östhammar | Sweden
> http://www.bitcycle.com/
> Phone: +46-73-753 24 62
> E-mail: jens at bitcycle.com
> 
> _______________________________________________
> swift-dev mailing list
> swift-dev at swift.org
> https://lists.swift.org/mailman/listinfo/swift-dev