From: John Carter <john.carter@...>
Date: 2007-05-25T07:34:34+09:00
Subject: Re: optimizing for speed - Array#each

On Thu, 24 May 2007, Mike Steiner wrote:

> I ran the profiler on my program and it said that 51% of the time is spent
> in Array#each. Is there any way to speed this up (like using
> Array#each_index perhaps)?

Mostly what the profiler is telling you is "don't do that".

Which sometimes isn't very helpful.

The thing to do rather than ask "is there something faster than
Array#each?" rather ask is there a way I can rewrite my algorithm so I
don't called Array#each so much?

I tend to not look at those entries in the profiler output and skip
downwards until I find the first method I wrote and optimize that.

> And is there a quicker way to do a .gsub if I'm using just strings and not a
> regexp?

I don't know exactly what you're doing but String []= does a lot more
than I would naively think.

------------------------------------------------------------- String#[]=
      str[fixnum] = fixnum
      str[fixnum] = new_str
      str[fixnum, fixnum] = new_str
      str[range] = aString
      str[regexp] = new_str
      str[regexp, fixnum] = new_str
      str[other_str] = new_str
------------------------------------------------------------------------
      Element Assignment---Replaces some or all of the content of _str_.
      The portion of the string affected is determined using the same
      criteria as +String#[]+. If the replacement string is not the same
      length as the text it is replacing, the string will be adjusted
      accordingly. If the regular expression or string is used as the
      index doesn't match a position in the string, +IndexError+ is
      raised. If the regular expression form is used, the optional second
      +Fixnum+ allows you to specify which portion of the match to
      replace (effectively using the +MatchData+ indexing rules. The
      forms that take a +Fixnum+ will raise an +IndexError+ if the value
      is out of range; the +Range+ form will raise a +RangeError+, and
      the +Regexp+ and +String+ forms will silently ignore the
      assignment.


> By the way, the program compares 2 databases and determines which records
> have been inserted and deleted, and each database has about 15,000 records
> to compare.

Have a look at
  http://rubygarden.org:3000/Ruby/page/show/RubyOptimization
for more info.

If you are still stuck, and it doesn't reveal any confidential
details, send the top 50 lines profiler output to the group and ask
for suggestions.


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand