A short presentation about HTTP caching at the Rome PHP User Group.

1. HTTP cache
Alessandro Nadalin
March, 29th 2011

2. The Web
is
inconsistent

3. get over it

4. Why?

5. Because it scales to billions of
users

6. Because it scales to billions of
users
WWW data traffic won't be
possible without being
inconsistent

7. How does it
scales?

8. Cache

9. What is caching?

10. Storing data so that future requests for that data can be served
faster
( general purpose )

11. Process of storing copies of your most accessed resources near
to a/some client/s
( the WWW )

12. Caching is not saving a webpage, or a fragment of it, on the
disk, to serve it to the next client

13. Caching is not saving a webpage, or a fragment of it, on the
disk, to serve it to the next client
This is a caching mechanism

14. Disk-persisted or in-memory

15. Can be distributed

16. Can be distributed with a NoSQL database

17. Cache implementation can be really funny

18. Don't reinvent the
wheel

19. Goals

20. Goals
evolve

21. Goals
evolve
loose coupling

22. Goals
Work less
evolve
loose coupling

23. Evolve
Because you want your platform to extensible

24. Evolve
Because you want your platform to extensible
Loose coupling
Because you want it to be easy to integrate with, evolve, plug
and mantain

25. Evolve
Because you want your platform to extensible
Loose coupling
Because you want it to be easy to integrate with, evolve, plug
and mantain
Work less
Because every LoC is bug-prone and our man-day is a hard to
scale cost

26. enters our Hero #1

29. enters our Hero #2

31. http://www.lullabot.com/articles/a-beginners-guide-to-caching-data

32. Goals
Work less
evolve
loose coupling

33. Goals
Work less
evolve
loose coupling

34. everything is done for us!
:)
but....

35. tmp files, cache tables, procedural crap...
mmmmh....
gotta be something better

36. Frameworks

38. Cache is used for compiling routes, autoloading, ...

39. Cache is used for compiling routes, autoloading, ...
...but also for storing the view

40. Goals
Work less
evolve
loose coupling

41. Goals
Work less
evolve
loose coupling

42. at least because we use a framework

43. but, probably

44. PHP sucks

45. Let's call a hero, from the East

46. on Rails

48. Goals
Work less
evolve
loose coupling

49. gosh :-(

50. hey, what about
the latest
products?

51. both Symfony2 and
Ruby's Rack embrace

52. HTTP

53. (here comes the nice part)

54. Local
Shared/proxy
Shared/reverse proxy

55. Local
Shared/proxy
Shared/reverse proxy

57. Local
Shared/proxy
Shared/reverse proxy

59. Local
Shared/proxy
Shared/reverse proxy

61. on the server side

62. Proxy Reverse proxy
http://www.codeproject.com/KB/aspnet/ExploringCaching.aspx

63. There is something cool about
caching softwares.

64. Free as free beer

65. ...but the server should
take advantage of them
( the boring part were you need to write code )

66. and here are a few ways to do so,
using

67. and here are a few ways to do so,
using
expiration

68. and here are a few ways to do so,
using
expiration
validation

69. and here are a few ways to do so,
using
expiration
validation
invalidation

70. and here are a few ways to do so,
using
expiration
validation
we will se why
invalidation

71. Expiration

72. GET / HTTP/1.1
Host: www.example.com
Expires: 0

73. GET / HTTP/1.1
Host: www.example.com
Expires: 0

74. GET / HTTP/1.1
Host: www.example.com
Expires: Tue, 15 Nov 1994 01:00 GMT

75. GET / HTTP/1.1
Host: www.example.com
Cache-Control: max-age=60, public

76. GET / HTTP/1.1
Host: www.example.com
Cache-Control: max-age=60, public

77. GET / HTTP/1.1
Host: www.example.com
Cache-Control: max-age=60, public
Cacheable for 60 seconds

78. GET / HTTP/1.1
Host: www.example.com
Cache-Control: max-age=60, public
Cacheable by both local and shared caches

79. GET / HTTP/1.1
Host: www.example.com
Cache-Control: stale-if-error=600, stale-while-revalidate=600

80. GET / HTTP/1.1
Host: www.example.com
Cache-Control: stale-if-error=600, stale-while-revalidate=600
fault-tolerant

81. GET / HTTP/1.1
Host: www.example.com
Cache-Control: stale-if-error=600, stale-while-revalidate=600
available during downtime

82. GET / HTTP/1.1
Host: www.example.com
Cache-Control: stale-if-error=600, stale-while-revalidate=600
available during revalidation

83. Validation

84. GET / HTTP/1.1
Host: www.example.com
Etag: 1234

85. GET / HTTP/1.1
Host: www.example.com
Etag: 1234
an identifier for your response

86. Conditional requests
GET / HTTP/1.1
Host: www.example.com
If-None-Match: 1234
the browsers asks you if it has been modified

87. Relax

88. Calculating an Etag is cheaper than generating a full MVC response

89. HTTP/1.1 304 Not Modified

90. GET / HTTP/1.1
Host: www.example.com
Last-Modified: Tue, 15 Jan 2011 12:00:00 GMT

91. GET / HTTP/1.1
Host: www.example.com
Last-Modified: Tue, 15 Jan 2011 12:00:00 GMT
tell the client about the latest change

92. Conditional requests
GET / HTTP/1.1
Host: www.example.com
If-Modified-Since: Tue, 15 Jan 2011 12:00:00 GMT
the client asks you if it has been modified since the last time

93. Relax

94. Calculating a date is cheaper than retrieving an entire object

95. HTTP/1.1 304 Not Modified

96. Invalidation

97. The web is not meant for invalidating data.
Server should not be able to keep clients' state, otherwise they
wont scale well.
That's why long-polling and endless connections haven't had
big success dealing with caching.

98. but hey, you say

99. HTTP's cache fails when dealing with really dynamic pages,
because consumers will always have to hit the origin server,
although a part of the page would be cacheable ( header and
footer, for example )

100. Nope
Nope

101. ESI was built for that
http://www.w3.org/TR/esi-lang

102. and hey, Varnish is a reverse proxy implementing what you
need of the ESI specification
take 2, pay for 1

103. So what does HTTP cache is meant to solve?

104. Less work

105. http://www.flickr.com/photos/snakphotography/5004775320/sizes/o/in/photostream/
because the hard work is delegated to the browser/proxy

106. evolve

107. because cache is abstracted from the application

108. loose coupling

109. because caching is bound to the protocol, HTTP, not
to your implementation ( Sf, RoR, Django )

110. The presentations lacks on technical stuff
So here are a few resource for who wants documentation:
http://tomayko.com/writings/things-caches-do
http://www.slideshare.net/fabpot/caching-on-the-edge
http://www.odino.org/301/rest-better-http-cache
http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html

111. Deep version of the same talk,
about Sf2 cache internals and ESI

112. May, 12/14 2011 in Verona
Early bid ends on April, 6th

113. Thanks!
Alessandro Nadalin
@_odino_
odino.org