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HTTP's Best-Kept Secret: Caching

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rtomayko

The document discusses HTTP caching as a way to improve performance. It describes different types of caches, including client caches, shared proxy caches, and gateway caches. Caching can save bandwidth and reduce response times. The document recommends using expiration dates and validation techniques like ETags and conditional GET requests to take advantage of caching. It provides code examples for setting cache headers and checking for stale content in Rails and Sinatra applications.

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Caching HTTP’s Best Kept Secret
Ryan Tomayko http://tomayko.com/
Sinatra http://www.sinatrarb.com
Rack http://rack.rubyforge.org
Rack::Cache http://tomayko.com/src/rack-cache
Heroku http://heroku.com
HTTP Caching?
NOT Rails Caching
GET /foo HTTP/1.1 Host: www.foo.com User-Agent: FooBrowser/1.0 Cache-Control: max-age=0 If-Modified-Since: Mon, 01 Jan 1979 ... If-None-Match: abcdef0123456789 Accept: * HTTP/1.1 200 OK Content-Type: text/html Content-Length: 24 Cache-Control: max-age=300 Last-Modified: Mon, 02 Jan 1979 ... ETag: abcdef0123456789 Vary: Accept
GET /foo HTTP/1.1 Host: www.foo.com User-Agent: FooBrowser/1.0 Cache-Control: max-age=0 If-Modified-Since: Mon, 01 Jan 1979 ... If-None-Match: abcdef0123456789 Accept: * HTTP/1.1 200 OK Content-Type: text/html Content-Length: 24 Cache-Control: public, max-age=300 Last-Modified: Mon, 02 Jan 1979 ... ETag: abcdef0123456789 Vary: Accept
Types of Caches
Client Cache Client Client Client Cache Cache Cache foo.com
Shared Proxy Cache Shared Proxy Cache foo.com
Shared Proxy Cache Cache Cache foo.com
Shared Proxy Cache
Gateway Cache foo.com Gateway Cache Backend
Caches Everywhere Client Client Cache Cache Shared Cache foo.com Gateway Cache Backend
Why Cache?
November 1990
November 1990 Web Population: 1
HTTP's Best-Kept Secret: Caching
February 1996 Web Population: 20M
February 1996 Modem Speed: 28.8kbps
February 1996
February 1996
Bandwidth.
February 1996 RFC 1945 - HTTP/1.0
March 1999 RFC 2616 - HTTP/1.1
Today
Expiration
Gateway Cache Alice Backend
Gateway Cache Alice Backend GET /foo Host: foo.com
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK Cache-Control:public,max-age=60
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK 200OK Cache-Control:public,max-age=60 Cache-Control:public,max-age=60
Gateway Cache Bob (30 seconds later) Backend
Gateway Cache Bob (30 seconds later) Backend GET /foo Host: foo.com
Gateway Cache Bob (30 seconds later) Backend GET /foo Host: foo.com 200OK Cache-Control:public,max-age=60 Age:30
Gateway Cache Carol (60 seconds later) Backend
Gateway Cache Carol (60 seconds later) Backend GET /foo Host: foo.com
Gateway Cache Carol (60 seconds later) Backend GET /foo GET /foo Host: foo.com Host: foo.com
Gateway Cache Carol (60 seconds later) Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK Cache-Control:public,max-age=60
Gateway Cache Carol (60 seconds later) Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK 200OK Cache-Control:public,max-age=60 Cache-Control:public,max-age=60
expires_in class FooController < Application def show expires_in 60.seconds, :public => true @foo = Foo.find(params[:id]) render :action => 'show' end end
Sinatra get '/foo' do headers['Cache-Control'] = 'public, max-age=60' @foo = Foo.find_and_stu erb :foo end
Validation (Conditional GET)
Gateway Cache Alice Backend
Gateway Cache Alice Backend GET /foo Host: foo.com
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK ETag:quot;abcdef012345quot;
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK 200OK ETag:quot;abcdef012345quot; ETag:quot;abcdef012345quot;
Gateway Cache Bob Backend
Gateway Cache Bob Backend GET /foo Host: foo.com
Gateway Cache Bob Backend GET /foo GET /foo Host: foo.com Host: foo.com If-None-Match: abcdef012345
Gateway Cache Bob Backend GET /foo GET /foo Host: foo.com Host: foo.com If-None-Match: abcdef012345 304NotModified
Gateway Cache Bob Backend GET /foo GET /foo Host: foo.com Host: foo.com If-None-Match: abcdef012345 304NotModified 200OK ETag:abcdef012345
Rails: fresh_when class FooController Application def show @foo = Foo.find(params[:id]) fresh_when :etag = @foo, :last_modified = @foo.updated_at.utc end end
Rails: stale? class FooController Application def show @foo = Foo.find(params[:id]) modified = @foo.updated_at.utc if stale?(:etag = @foo, :last_modified = modified) respond_to do |wants| # ... normal response processing end end end end
Sinatra: etag get '/foo' do @foo = Foo.find(params[:id]) etag @foo.etag erb :foo end
Expiration + Validation
Gateway Cache Alice Backend
Gateway Cache Alice Backend GET /foo Host: foo.com
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK Cache-Control:public,max-age=60 ETag:abcdef012345
Gateway Cache Alice Backend GET /foo GET /foo Host: foo.com Host: foo.com 200OK 200OK Cache-Control:public,max-age=60 Cache-Control:public,max-age=60 ETag:abcdef012345 ETag:abcdef012345
Gateway Cache Bob (30 seconds later) Backend
Gateway Cache Bob (30 seconds later) Backend GET /foo Host: foo.com
Gateway Cache Bob (30 seconds later) Backend GET /foo Host: foo.com 200OK Cache-Control:public,max-age=60 ETag:abcdef012345 Age:30
Gateway Cache Carol (60 seconds later) Backend
Gateway Cache Carol (60 seconds later) Backend GET /foo Host: foo.com
Gateway Cache Carol (60 seconds later) Backend GET /foo GET /foo Host: foo.com Host: foo.com If-None-Match: abcdef012345
Gateway Cache Carol (60 seconds later) Backend GET /foo GET /foo Host: foo.com Host: foo.com If-None-Match: abcdef012345 304NotModified Cache-Control:public,max-age=60
Gateway Cache Carol (60 seconds later) Backend GET /foo GET /foo Host: foo.com Host: foo.com If-None-Match: abcdef012345 200OK 304NotModified Cache-Control:public,max-age=60 Cache-Control:public,max-age=60 ETag:abcdef012345
Never Generate The Same Response Twice
use Rack::Cache $ gem install rack-cache config.middleware.use Rack::Cache, :verbose = true, :metastore = quot;file:/var/cache/rack/metaquot;, :entitystore = quot;file:/var/cache/rack/bodyquot;, :allow_reload = false, :allow_revalidate = false
High Performance Caches/Accelerators •Squid http://www.squid-cache.org/ • Varnish http://varnish.projects.linpro.no/
Heroku
Thanks!

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HTTP's Best-Kept Secret: Caching

Editor's Notes

  • #6: Pure ruby HTTP cache implementation. This talk is not really about Rack::Cache.
  • #7: Heroku understands HTTP caching.
  • #8: What we're talking about when we say HTTP caching. There's so many different caching systems.
  • #9: Page caching, action caching, fragment caching, SQL caching, memcached.
  • #10: *This* is what we're talking about Wire level Declarative. Don't worry if this doesn't look familiar.
  • #12: All caches adhere to the same basic rules for the most part.
  • #13: Or browser cache. People are most familiar with. When we think about HTTP caching, this is what comes to mind. Bandwidth/Traffic Reduction. Number of Clients served by the Cache. I don&#x2019;t want to talk about Client caches.
  • #14: Many users behind a single cache
  • #17: Also Known As &#x201C;Reverse Proxy Cache&#x201D;
  • #19: The reasons have changed over time.
  • #21: First server, client/browser, and web page Things are good for, like, a year. Ramble about research guys trading papers and linking to each other.
  • #22: Explosive Netscape goes public in 1995
  • #23: State of the art Roughly 2.3KB/s Today, yahoo.com homepage is 388K - 2m48s
  • #24: Other things: CGI just starting out. (Guestbooks, hit counters, search) JavaScript - didn&#x2019;t exist. So what was the most important issue to solve?
  • #26: Expires Last-Modified
  • #27: Cache-Control ETag
  • #28: Much more worried about load on backends. Do less work.
  • #47: I use ETag and If-None-Match. Last-Modified and If-Modified-Since.
  • #48: I use ETag and If-None-Match. Last-Modified and If-Modified-Since.
  • #49: I use ETag and If-None-Match. Last-Modified and If-Modified-Since.
  • #50: I use ETag and If-None-Match. Last-Modified and If-Modified-Since.
  • #53: Halts
  • #66: Requires Rails 2.3+ for Rack/middleware support.