Ruby 1.9.3 (Rails 3) Ruby 2.0 (Rails 4) Performance test and improvements

Using Mac OS and Webrick in local environment
time -p bundle exec rake environment
real 6.69
user 4.76
sys 0.79

export RUBY_GC_MALLOC_LIMIT=1000000000
export RUBY_FREE_MIN=500000
export RUBY_HEAP_MIN_SLOTS=40000

AFTER we set the above exports , check the below performance
time -p bundle exec rake environment
real 5.36
user 3.19
sys 1.05

Also tested in request to response scenario using apache bench with 100 requests
Ruby 1.9.3 (Rails 3)
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ab -n 100 -c 1 http://localhost:3000/
------------------------------------------------------------------------------------------
BEFORE FLAGS SET  (ruby-1.9.3-p194 [ x86_64 ])
------------------------------
Server Software:        WEBrick/1.3.1
Server Hostname:        127.0.0.1
Server Port:            3000

Document Path:          /
Document Length:        96050 bytes

Concurrency Level:      1
Time taken for tests:   391.883 seconds
Complete requests:      100
Failed requests:        13
   (Connect: 0, Receive: 0, Length: 13, Exceptions: 0)
Write errors:           0
Total transferred:      9698686 bytes
HTML transferred:       9604985 bytes
Requests per second:    0.26 [#/sec] (mean)
Time per request:       3918.831 [ms] (mean)
Time per request:       3918.831 [ms] (mean, across all concurrent requests)
Transfer rate:          24.17 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:     2963 3585 583.6   3430    5625
Processing:     0  334 2625.5      1   26154
Waiting:        0  333 2625.5      0   26153
Total:       2963 3919 2905.2   3430   31529

Percentage of the requests served within a certain time (ms)
  50%   3430
  66%   3532
  75%   3623
  80%   3710
  90%   4407
  95%   6346
  98%   7244
  99%  31529
 100%  31529 (longest request)
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AFTER FLAGS SET  (ruby-1.9.3-p194 [ x86_64 ])
---------------------------------------------------------------
export RUBY_GC_MALLOC_LIMIT=1000000000
export RUBY_FREE_MIN=500000
export RUBY_HEAP_MIN_SLOTS=40000

Server Software:        WEBrick/1.3.1
Server Hostname:        127.0.0.1
Server Port:            3000

Document Path:          /
Document Length:        96050 bytes

Concurrency Level:      1
Time taken for tests:   368.903 seconds
Complete requests:      100
Failed requests:        14
   (Connect: 0, Receive: 0, Length: 14, Exceptions: 0)
Write errors:           0
Total transferred:      9714323 bytes
HTML transferred:       9620622 bytes
Requests per second:    0.27 [#/sec] (mean)
Time per request:       3689.025 [ms] (mean)
Time per request:       3689.025 [ms] (mean, across all concurrent requests)
Transfer rate:          25.72 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:     2563 3388 634.5   3395    5351
Processing:     0  301 2692.0      0   26860
Waiting:        0  301 2692.0      0   26859
Total:       2563 3689 2973.1   3397   32211

Percentage of the requests served within a certain time (ms)
  50%   3397
  66%   3656
  75%   3753
  80%   3809
  90%   3928
  95%   5208
  98%   6949
  99%  32211
 100%  32211 (longest request)
----------------------------------------------------

Ruby 2.0 (Rails 4)
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 ab -n 100 -c 1 http://127.0.0.1:3000/
------------------------------------------------------------------------------------------------------
Server Software:        WEBrick/1.3.1
Server Hostname:        127.0.0.1
Server Port:            3000

Document Path:          /?locale=uk
Document Length:        20815 bytes

Concurrency Level:      1
Time taken for tests:   181.485 seconds
Complete requests:      100
Failed requests:        5
   (Connect: 0, Receive: 0, Length: 5, Exceptions: 0)
Write errors:           0
Total transferred:      2185395 bytes
HTML transferred:       2081495 bytes
Requests per second:    0.55 [#/sec] (mean)
Time per request:       1814.851 [ms] (mean)
Time per request:       1814.851 [ms] (mean, across all concurrent requests)
Transfer rate:          11.76 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       37 1590 658.0   1678    5320
Processing:     0  225 918.2      0    8042
Waiting:        0  225 917.9      0    8041
Total:       1585 1815 818.9   1679    8079

Percentage of the requests served within a certain time (ms)
  50%   1679
  66%   1685
  75%   1690
  80%   1694
  90%   1749
  95%   1995
  98%   6240
  99%   8079
 100%   8079 (longest request)
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AFTER FLAG SET (Ruby 2.0 (Rails 4)
export RUBY_GC_MALLOC_LIMIT=1000000000
export RUBY_FREE_MIN=500000
export RUBY_HEAP_MIN_SLOTS=40000
----------
Server Software:        WEBrick/1.3.1
Server Hostname:        127.0.0.1
Server Port:            3000

Document Path:          /?locale=uk
Document Length:        20815 bytes

Concurrency Level:      1
Time taken for tests:   172.496 seconds
Complete requests:      100
Failed requests:        12
   (Connect: 0, Receive: 0, Length: 12, Exceptions: 0)
Write errors:           0
Total transferred:      2185386 bytes
HTML transferred:       2081486 bytes
Requests per second:    0.58 [#/sec] (mean)
Time per request:       1724.962 [ms] (mean)
Time per request:       1724.962 [ms] (mean, across all concurrent requests)
Transfer rate:          12.37 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       36  350 695.0     40    3408
Processing:     0 1374 737.0   1564    3935
Waiting:        0 1374 736.6   1563    3934
Total:       1582 1725 406.2   1607    3973

Percentage of the requests served within a certain time (ms)
  50%   1607
  66%   1617
  75%   1640
  80%   1651
  90%   1909
  95%   3031
  98%   3408
  99%   3973
 100%   3973 (longest request)

Upgrading tips for Ruby 2.0 & Rails 4 from Ruby 1.9.3 & Rails 3

Ruby  2.0
1. mostly compatible with Ruby 1.9.3 version
3. more refinements and code related features;
4. Asynchronous exception handling API
5. More built in libraries
6. Debugging support(DTrace,TracePoint)
7. Performace enhancements like GC optimization and better method dispatch
8. Customize VM ENV variables

Rails 4.0
0.Test coverage is should be good before starting an upgrade.
1. By default thread safe: so have to use gems which are thread safe
2. better utf-8 support
3. better with unicorn like servers
4. Rails 4 prefers Ruby 2.0 and requires 1.9.3 or newer.
5. Some ActionController classes moved to ActionDispatch
6.secret_key_base upgraded carefully , cookies signed based on the new secret_key_base in Rails 4.x are not backwards compatible with Rails( Wait for all users to accommodate new token )
7. Better caching (https://gist.github.com/szimek/1669330)
8.Official upgrade link
    http://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html
9. buy a book to upgrade rails 4 ?  here is the link : https://leanpub.com/upgradetorails4