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Put Down the Hammer On using the right tool for the job.

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Case Study: Tag Autocompleter

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The Naïve Solution

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The Naïve Solution

•Tag.find
:conditions
=>
[‘text
LIKE
?’,
...]

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The Naïve Solution

•Tag.find
:conditions
=>
[‘text
LIKE
?’,
...] •TagController#autocomplete

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That’s not so bad, is it?

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What is important for an autocompleter?

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SPEED

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Let’s enumerate the steps to get the tags.

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Ajax Call

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Ajax Call Nginx

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Ajax Call Nginx Router

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Ajax Call Nginx Router Action

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Ajax Call Nginx Router Action Tag.find

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Ajax Call Nginx Router Action Tag.find MySQL full table scan

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Ajax Call Nginx Router Action Tag.find MySQL full table scan Map rows to ActiveRecord objects

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Ajax Call Nginx Router Action Tag.find MySQL full table scan Map rows to ActiveRecord objects Render JSON/HTML

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Ajax Call Nginx Router Action Tag.find MySQL full table scan Map rows to ActiveRecord objects Render JSON/HTML Respond

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Ajax Call Nginx Router Action Tag.find MySQL full table scan Map rows to ActiveRecord objects Render JSON/HTML Respond

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Ajax Call Nginx Router Action Tag.find MySQL full table scan Map rows to ActiveRecord objects Render JSON/HTML Respond Unnecessary steps that take up most of the time! Tyler McMullen

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How can we do this more efficiently?

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First, ditch the database.

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ActiveRecord and MySQL are overkill.

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Use a Trie.

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Use a Trie. (Shameless Plug: http://github.com/tyler/trie)

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B

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E

E

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A B

E E

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R

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B

A

R

T

E

A

R

E

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Use the right data structure for the job.

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Ajax Call Nginx Router Action Tag.find MySQL full table scan Map rows to ActiveRecord objects Render JSON/HTML Respond

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Ajax Call Nginx Router Action Trie#children(prefix) Render JSON/HTML Respond

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Ajax Call Nginx Router Action Trie#children(prefix) Render JSON/HTML Respond Our next victims!

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Next step is to sidestep the Rails app altogether.

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If not Rails... then what?!

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Rack is awesome for little web services.

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•Fast

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•Fast •Low Memory Usage

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•Fast •Low Memory Usage •Easy

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class
Autocompleter 

def
initialize 



@trie
=
Trie.load_file(file,
/(\w+)\|(\d+)/) 

end 

def
call(env) 



req
=
Rack::Request.new(env) 



words
=
@trie.children(req.params['query'])[0,5] 



[
200, 





{
"Content‐Type"
=>
"text/html"
}, 





[words.to_json]
] 

end end

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What about routing?

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location
/autocomplete
{ proxy_pass
http://autocompleter;
 
 }

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location
/autocomplete
{ proxy_pass
http://autocompleter;
 
 } (You are using Nginx, right?)

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Ajax Call Nginx Router Action Trie#children(prefix) Render JSON/HTML Respond

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Ajax Call Nginx Rack Service Trie#children(prefix) Render JSON/HTML Respond

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Does it really matter?

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It’s handling 200 requests per second.

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It’s handling 200 requests per second. On a single Thin instance.

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It’s handling 200 requests per second. On a single Thin instance. With a response time of 0.006s.

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It’s handling 200 requests per second. On a single Thin instance. With a response time of 0.006s. Takes up 18mb of ram.

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It’s handling 200 requests per second. On a single Thin instance. With a response time of 0.006s. Takes up 18mb of ram. And <1% cpu usage.

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It’s good for your users and your budget.

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Questions?

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