# Array performance question **URL:** \ **Category:** Ruby\ **Created:** [February 27, 2009, 2:18pm UTC](https://www.ruby-forum.com/t/array-performance-question/161569 "2009-02-27T14:18:29Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [February 27, 2009, 2:18pm UTC](https://www.ruby-forum.com/t/array-performance-question/161569/1 "2009-02-27T14:18:29Z")
Here’s a real Array performance mystery. I can’t help my friend figure this one out. He writes, ======== Is there a known bug in Ruby array performance? I spent a lot of time yesterday boiling down the following example [http://blogs.codehaus.org/people/geir/archives/001768\_baffled\_with\_ruby.html](http://blogs.codehaus.org/people/geir/archives/001768_baffled_with_ruby.html) only because I still can’t believe I’m not doing something incredibly stupid. (I’m a newbie, “Reluctant Rubyist”) I’m just not used to arrays behaving this way 🙂 Anyone have any insight? ======== He’d love a response in his blog, but with permission I’ll copy answers here over there. He’s not a regular ruby-talk reader…yet. Jim ---
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [February 27, 2009, 3:51pm UTC](https://www.ruby-forum.com/t/array-performance-question/161569/2 "2009-02-27T15:51:30Z")
2009/2/27 Jim M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > only because I still can’t believe I’m not doing something incredibly > stupid. Â (I’m a newbie, “Reluctant Rubyist”) > > Â I’m just not used to arrays behaving this way 🙂 Â Anyone have any > insight? > > ======== > > He’d love a response in his blog, but with permission I’ll copy > answers here over there. He’s not a regular ruby-talk reader…yet. Slightly modified test (attached): ## 15:44:06 Temp$ ruby bm.rb bm; ruby bm.rb bmbm; ruby19 bm.rb bm; ruby19 bm.rb bmbm 1.8.7 user system total real size = 10000 10000 0.125000 0.000000 0.125000 ( 0.114000) size = 100000 100000 0.859000 0.000000 0.859000 ( 0.863000) size = 1000000 1000000 24.969000 0.000000 24.969000 ( 24.961000) 1.8.7 Rehearsal size = 10000 10000 24.235000 0.032000 24.267000 ( 24.308000) size = 100000 100000 18.078000 0.000000 18.078000 ( 18.150630) size = 1000000 1000000 14.297000 0.000000 14.297000 ( 14.289000) ------------------------------------------------------- total: 56.642000sec ``` user system total ``` ## real size = 10000 10000 12.031000 0.000000 12.031000 ( 12.039000) size = 100000 100000 10.250000 0.000000 10.250000 ( 10.290950) size = 1000000 1000000 8.985000 0.000000 8.985000 ( 8.989000) 1.9.1 user system total real size = 10000 10000 0.016000 0.000000 0.016000 ( 0.027000) size = 100000 100000 0.031000 0.000000 0.031000 ( 0.028000) size = 1000000 1000000 0.047000 0.000000 0.047000 ( 0.043000) 1.9.1 Rehearsal size = 10000 10000 0.032000 0.000000 0.032000 ( 0.043000) size = 100000 100000 0.032000 0.000000 0.032000 ( 0.043000) size = 1000000 1000000 0.031000 0.000000 0.031000 ( 0.043000) -------------------------------------------------------- total: 0.095000sec ``` user system total ``` real size = 10000 10000 0.031000 0.000000 0.031000 ( 0.039000) size = 100000 100000 0.047000 0.000000 0.047000 ( 0.043000) size = 1000000 1000000 0.032000 0.000000 0.032000 ( 0.043000) Strange that the rehearsal has this dramatic effect. Normally it should simply execute the block twice to warm up the system. Kind regards robert ---
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [February 27, 2009, 4:24pm UTC](https://www.ruby-forum.com/t/array-performance-question/161569/3 "2009-02-27T16:24:27Z")
2009/2/27 Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Strange that the rehearsal has this dramatic effect. Â Normally it > should simply execute the block twice to warm up the system. Here’s a better test 16:16:32 Temp$ ruby bm.rb; ruby19 bm.rb 1.8.7 user system total real size = 10000 10000 0.110000 0.000000 0.110000 ( 0.118000) size = 100000 100000 0.781000 0.000000 0.781000 ( 0.769000) size = 1000000 1000000 25.172000 0.000000 25.172000 ( 25.185000) size = 10000 10000 0.328000 0.000000 0.328000 ( 0.329000) size = 100000 100000 0.547000 0.000000 0.547000 ( 0.542000) size = 1000000 1000000 18.156000 0.000000 18.156000 ( 18.151000) 1.9.1 user system total real size = 10000 10000 0.031000 0.000000 0.031000 ( 0.027000) size = 100000 100000 0.031000 0.000000 0.031000 ( 0.028000) size = 1000000 1000000 0.031000 0.000000 0.031000 ( 0.043000) size = 10000 10000 0.031000 0.000000 0.031000 ( 0.031000) size = 100000 100000 0.032000 0.000000 0.032000 ( 0.023000) size = 1000000 1000000 0.031000 0.000000 0.031000 ( 0.043000) “better” in the sense that we’re not suffering from bmbm’s magic. Kind regards robert ---
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [February 28, 2009, 7:10am UTC](https://www.ruby-forum.com/t/array-performance-question/161569/4 "2009-02-28T07:10:26Z")
Jim M. wrote: > Jim This variation exhibits the same behavior. require ‘benchmark’ class BufferContainer def initialize( initial\_data ) @buf = initial\_data end def put\_array( array ) @buf[0, array.size] = array end end size = 999 the\_array = (0…4).to\_a (1…3).each{|i| size \*= 10 a = [nil] \* size # RUN WITH THIS COMMENTED OUT FIRST # a \<\< 9 puts “size = #{ size } #{ a.size }” puts Benchmark.measure { 10\_000.times { buf = BufferContainer.new( a ) buf.put\_array( the\_array ) } } } ---
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [March 1, 2009, 6:34am UTC](https://www.ruby-forum.com/t/array-performance-question/161569/5 "2009-03-01T06:34:27Z")
On Feb 27, 2009, at 05:16 , Jim M. wrote: > Is there a known bug in Ruby array performance? I spent a lot of time > yesterday boiling down the following example > > [http://blogs.codehaus.org/people/geir/archives/001768\_baffled\_with\_ruby.html](http://blogs.codehaus.org/people/geir/archives/001768_baffled_with_ruby.html) I don’t have time to dig into this, but I believe he’s hitting a GC threshold by going over N objects. ---
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [March 1, 2009, 6:36am UTC](https://www.ruby-forum.com/t/array-performance-question/161569/6 "2009-03-01T06:36:13Z")
On Feb 28, 2009, at 21:32 , Ryan D. wrote: > threshold by going over N objects. > Poke around gc.c and see what you can figure out. Also, look at the > 1.9 version or through the changelog to find hints… #ifndef GC\_MALLOC\_LIMIT #if defined(MSDOS) || defined( **human68k** ) #define GC\_MALLOC\_LIMIT 200000 #else #define GC\_MALLOC\_LIMIT 8000000 #endif #endif ---
**Author:** ![wolfmanjm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/3da27b/32.png) [@wolfmanjm](https://www.ruby-forum.com/u/wolfmanjm)\ **Post date:** [March 10, 2009, 3:06pm UTC](https://www.ruby-forum.com/t/array-performance-question/161569/7 "2009-03-10T15:06:24Z")
Jim M. wrote: > Jim I am betting Ryan is right about GC issues. JRuby does not fall down doing this either (which probably also backs up the GC theory): ruby ~/jruby/scripts/arr\_ben.rb size = 10000 10000 0.050000 0.000000 0.050000 ( 0.057190) size = 100000 100000 0.660000 0.000000 0.660000 ( 0.672178) size = 1000000 1000000 34.430000 0.340000 34.770000 ( 35.562454) jruby --server ~/jruby/scripts/arr\_ben.rb size = 10000 10000 0.372000 0.000000 0.372000 ( 0.266000) size = 100000 100000 0.099000 0.000000 0.099000 ( 0.099000) size = 1000000 1000000 0.154000 0.000000 0.154000 ( 0.154000) -Tom