Forum: Ruby 1.9.1 regex 6.5 times slower than 1.8.6 in at least one case

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C742175a04e90db217deaf3650ef5d30?d=identicon&s=25 Michael Brooks (Guest)
on 2009-02-24 03:19
(Received via mailing list)
Hello:

In general I've found Ruby 1.9.1 to be 2 times faster than 1.8.6 and
roughly the same speed as Python 2.8 which is great... thanks guys,
great job!

However, in one case, when using a regular expressions (posted here by
someone a long time ago) which I use to determine what numbers in
0..10000 are prime numbers, version 1.9.1 was at least 6.5 times slower
(1.8.6 = 67 secs, 1.9.1 = 457 secs).

The regular express is:

     ((("1" * self) =~ /^1$|^(11+?)\1+$/) == nil)

which I've used in different versions of my program running either on
its own or as part of an overloading function as follows:

   # Add an "is_prime?" method to the built-in numeric class
   # which returns true if the number is a prime number.
   class Fixnum
     def is_prime?
       ((("1" * self) =~ /^1$|^(11+?)\1+$/) == nil)
     end
   end

I also have a version of the prime-number calculation program that which
doesn't use the above regex (i.e. it uses a traditional brute force
approach instead) and it runs 2 times faster in 1.9.1.  In 1.9.1 the
regex gets exponentially worse as the number being evaluated exceeding
1000.

Does anyone know why the regex in 1.9.1 is so much slower than 1.8.6?

Thank You,

Michael
E0526a6bf302e77598ef142d91bdd31c?d=identicon&s=25 Daniel DeLorme (Guest)
on 2009-02-24 08:02
(Received via mailing list)
Michael Brooks wrote:
> However, in one case, when using a regular expressions (posted here by
> someone a long time ago) which I use to determine what numbers in
> 0..10000 are prime numbers, version 1.9.1 was at least 6.5 times slower
> (1.8.6 = 67 secs, 1.9.1 = 457 secs).
>
> The regular express is:
>
>     ((("1" * self) =~ /^1$|^(11+?)\1+$/) == nil)

As the only guy who would rather use a regex rather than string slicing,
that's disheartening news. One thing you might want to check is your
encoding. If your default encoding is UTF8, some string operations can
be significantly slower:

$ cat p-regex.rb
4000.times do |i|
   ((("1" * i) =~ /^1$|^(11+?)\1+$/) == nil)
end

$ time 1.8/bin/ruby -KN -v p-regex.rb
ruby 1.8.6 (2008-08-11 patchlevel 287) [i686-linux]
real  0m4.411s
user  0m4.292s
sys  0m0.032s

$ time 1.8/bin/ruby -KU -v p-regex.rb
ruby 1.8.6 (2008-08-11 patchlevel 287) [i686-linux]
real  0m4.480s
user  0m4.320s
sys  0m0.004s

$ time 1.9/bin/ruby -KN -v p-regex.rb
ruby 1.9.1p0 (2009-02-22 revision 22551) [i686-linux]
real  0m8.041s
user  0m7.980s
sys  0m0.020s

$ time 1.9/bin/ruby -KU -v p-regex.rb
ruby 1.9.1p0 (2009-02-22 revision 22551) [i686-linux]
real  0m21.709s
user  0m20.913s
sys  0m0.032s

With ascii encoding, ruby1.9 is still slower than 1.8 but at least not
six times slower.
C742175a04e90db217deaf3650ef5d30?d=identicon&s=25 Michael Brooks (Guest)
on 2009-02-25 07:25
(Received via mailing list)
Daniel DeLorme wrote:
> As the only guy who would rather use a regex rather than string slicing,
> ruby 1.8.6 (2008-08-11 patchlevel 287) [i686-linux] > real  0m4.411s
> With ascii encoding, ruby1.9 is still slower than 1.8 but at least not
> six times slower.
>
> Daniel
>

Hello Daniel:

Interesting, I didn't know about those switches.

I ran my 10000 iteration prime number calc program using ruby 1.9.1 with
no switch then with the two switches you identified:

ruby "fprim v5.rb" > 477.47 seconds
ruby -KN "fprim v5.rb" > 500.89 seconds
ruby -KU "fprim v5.rb" > 1059.04 seconds

Each test was run twice and the lower number from each reported above.
I'm not sure why it's slower than the numbers I first reported.

I'm running Windows XP (which I know is slower than Linux and the
default Windows compiled binaries for 1.9.1 might be having some impact
too) on an unplugged AMD 1.9 GHz based laptop (it runs at about 1.1 GHz
when unplugged) with 2 GB ram.  I'm not sure what my default ruby
encoding is but it appears to be a bit faster than the -KN switch.

To put those numbers in perspective, if I run your code on my unplugged
laptop with the -KN switch it takes 37.07 seconds and without any switch
36.85 seconds.  If I change your code to use 10000 iterations and run it
with the -KN switch it takes 477.36 seconds and without any switch
500.44 seconds (which is strange because it's a flip of numbers in the
fprim test).

All I can say regarding regex performance and 1.9.1 is OUCH.

Michael
A87f7a014c624587fab0d3d78c5b9c18?d=identicon&s=25 BIl Kleb (Guest)
on 2009-02-25 07:45
(Received via mailing list)
Michael Brooks wrote:
>
> However, in one case, when using a regular expressions (posted here by
> someone a long time ago) which I use to determine what numbers in
> 0..10000 are prime numbers, version 1.9.1 was at least 6.5 times slower
> (1.8.6 = 67 secs, 1.9.1 = 457 secs).

I found similar results lately, but the difference was more like a
factor of 12!

RUBY 1.8.6:

$ cd FUN3D
$ find . -name \*_c.\?90 -exec rm {} \;
$ time ruby Ruby/complex_transformations_spike.rb
[...]
real    0m25.221s
user    0m22.292s
sys    0m0.759s

$ ruby -v
ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0]
(as comes with OS X)

RUBY 1.9.1:

$ cd /usr/local/src
$ wget ftp://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.1-p0.tar.gz
$ tar zxf ruby-1.9.1-p0.tar.gz
$ cd ruby-1.9.1-p0
$ ./configure --program-suffix=19 --enable-shared
$ make
$ sudo make install
$ cd -

$ time ruby19 Ruby/complex_transformations_spike.rb
[...]
real    5m18.188s
user    4m54.253s
sys    0m2.866s

$ ruby19 -v
ruby 1.9.1p0 (2009-01-30 revision 21907) [i386-darwin9.6.0]

Regards,
Cec345a59245af9d06e4438a413f4eb5?d=identicon&s=25 Shot (Piotr Szotkowski) (Guest)
on 2009-03-30 00:39
(Received via mailing list)
// I’m slowly trawling through my ruby-talk backlog, so apologies
// if the below is irrelevant to anyone at this point in time. :)

Michael Brooks:

> However, in one case, when using a regular expressions (posted here by
> someone a long time ago) which I use to determine what numbers in
> 0..10000 are prime numbers, version 1.9.1 was at least 6.5 times
> slower  (1.8.6 = 67 secs, 1.9.1 = 457 secs).

> The regular express is:

>     ((("1" * self) =~ /^1$|^(11+?)\1+$/) == nil)

> which I've used in different versions of my program running either
> on  its own or as part of an overloading function as follows:

>   # Add an "is_prime?" method to the built-in numeric class
>   # which returns true if the number is a prime number.
>   class Fixnum
>     def is_prime?
>       ((("1" * self) =~ /^1$|^(11+?)\1+$/) == nil)
>     end
>   end

Note that this is a really ineffective way of testing primarity:

ruby 1.9.1p0 (2009-01-30 revision 21907) [i686-linux]
>> class Fixnum
>>   def is_prime?
>>     ((("1" * self) =~ /^1$|^(11+?)\1+$/) == nil)
>>   end
>> end
=> nil
>> require 'prime' # adds Fixnum#prime? (among others)
=> true
>> start = Time.now; (0..1000).select(&:is_prime?); Time.now - start
=> 0.405157579
>> start = Time.now; (0..1000).select(&:prime?); Time.now - start
=> 0.016556705
>> start = Time.now; (0..5000).select(&:is_prime?); Time.now - start
=> 30.165383712
>> start = Time.now; (0..5000).select(&:prime?); Time.now - start
=> 0.105887884

Note that the Prime class has two bugs (as of 1.9.1-p0, both will be
fixed in the next 1.9.1 release), but your regex also has one of them:

>> 0.is_prime?
=> true # BUG
>> 1.is_prime?
=> false
>> 0.prime?
=> true # BUG
>> 1.prime?
=> true # BUG

(Neither 0 nor 1 are prime numbers.)

> I also have a version of the prime-number calculation program that
> which doesn't use the above regex (i.e. it uses a traditional brute
> force approach instead) and it runs 2 times faster in 1.9.1.

I highly recommend http://ruby-doc.org/core-1.9/ → Prime class (et al.).

— Shot
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