test.rb

require "sqlite3"
require "benchmark"

FileUtils.rm_f("test.db")
def open_db
  db = SQLite3::Database.new "test.db"
end

def create_db
  db = open_db
  db.execute "BEGIN"
  # Based on tool/speedtest.tcl from sqlite
  db.execute <<-SQL
  create table t2 (a INTEGER, b INTEGER, c VARCHAR(100));
  SQL

  1.upto(25000) do |i|
    r = rand(500000)
    db.execute "INSERT INTO t2 VALUES(#{i},#{r},'[number_name #{r}]');"
  end
  db.execute "COMMIT"
end

def run_test(db = open_db)
  i = 0
  while i < 10000
    sql = <<~SQL
    SELECT count(*), avg(b) FROM t2 WHERE b>=#{i} AND b<#{i + 1000};
    SQL
    db.execute(sql)
    i += 100
  end
end

def run_tests(n=10, threaded: false)
  if threaded
    n.times.map { Thread.new { run_test } }.map(&:join)
  else
    n.times { run_test }
  end
end

create_db
run_test

puts "single threaded:"
puts Benchmark.realtime { run_tests(threaded: false) }

puts "multi threaded:"
puts Benchmark.realtime { run_tests(threaded: true) }

sqlite3-ruby master

$ bundle exec ruby test.rb
single threaded:
0.9432485040742904
multi threaded:
1.1921860249713063

With (incomplete, hacky) GVL release patch:

$ bundle exec ruby test.rb
single threaded:
0.927121008047834
multi threaded:
0.17125224182382226