Summary

Line-by-line string parsing (splitting and iterating over lines) is significantly slower in JRuby 10 compared to JRuby 1.7.

Benchmark

require 'benchmark'

text = ("Line of text number X\n" * 50_000)
n = 100

Benchmark.bm(20) do |x|
  x.report("each_line") { n.times { text.each_line { |line| line } } }
  x.report("lines.each") { n.times { text.lines.each { |line| line } } }
  x.report("split(newline)") { n.times { text.split("\n").each { |line| line } } }
end

Results

JRuby 1.7 was faster than MRI for line parsing. JRuby 10 is now 2x slower than MRI and 3.6x slower than JRuby 1.7.

Impact

Affects applications doing:

• Log file processing
• CSV/text file parsing
• Any line-oriented I/O operations

Environment

• JRuby 10.0.2.0 on Java 21 (Temurin 21.0.9)
• JRuby 1.7.27 on Java 8 (Corretto 8.472)
• MRI 3.4.7
• macOS Darwin 25.1.0