Backport #2722: gets on a large file takes a very very long time

• Status: Closed
• Assignee: -

[ghazel (Greg Hazel)]

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This problem occurs on 1.8.6, 1.8.7 and 1.9.1 (all the versions I tested)

This simple script demonstrates the problem:

100 MB

n = 100 * 1000 * 1000
puts "writing"
File.open("foo", 'wb'){|f| f.write(" " * n) }
puts "reading"
File.open("foo", 'rb') do |io|
io.gets
end

This takes about 1911 seconds. Using a 10MB file completes in 19 seconds, instead of in 1/10th the time as you would imagine. Similarly a 1MB file completes in 0.18 seconds.
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[matz (Yukihiro Matsumoto)]

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Hi,

In message "Re: [ruby-core:28103] [Bug #2722] gets on a large file takes a very very long time"
on Mon, 8 Feb 2010 17:33:09 +0900, Greg Hazel [e-mail] writes:

|This problem occurs on 1.8.6, 1.8.7 and 1.9.1 (all the versions I tested)

I could reproduce the problem on 1.9, but not on 1.8. 1.9 has been
fixed by r26622. Thank you for the report.

						matz.

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[matz (Yukihiro Matsumoto)]

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Hi,

In message "Re: [ruby-core:28138] Re: [Bug #2722] gets on a large file takes a very very long time"
on Wed, 10 Feb 2010 06:09:54 +0900, Roger Pack [e-mail] writes:

|For me it performs fast when I replace .gets with .read
|Perhaps there is a reason for this?

gets need to scan for the newline. Here's my numbers

ruby 1.9.2dev (2010-02-09 trunk 26623) [i686-linux]
gets: 0.13s user 0.42s system 88% cpu 0.626 total
read: 0.08s user 0.46s system 93% cpu 0.578 total

ruby 1.8.8dev (2010-02-07 revision 26612) [i486-linux]
gets: 2.54s user 0.44s system 97% cpu 3.073 total
read: 2.47s user 0.45s system 97% cpu 3.007 total

1.8 has bottleneck on String#times, maybe we can work on it.

						matz.

=end

[naruse (Yui NARUSE)]

• Priority changed from Normal to 3

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=end

[jeremyevans0 (Jeremy Evans)]

• Tracker changed from Bug to Backport
• Project changed from 2 to 5
• Description updated (diff)
• Status changed from Open to Closed
• ruby -v deleted (ruby 1.8.6 (2009-08-04 patchlevel 383) [i386-mingw32])