Memcached Install, Overview & Benchmarks What is Memcached? - - PowerPoint PPT Presentation

Memcached

Install, Overview & Benchmarks

What is Memcached?

• Really, its Memcache-d (d as in daemon)
• TCP/IP service that allows you to store

stuff in RAM, somewhat persistently

• Basically, a persistent hash table
• Super awesome

Getting Started

• Download the memcached source code

(http://www.danga.com/memcached/)

• Download the memcached PHP extension
• Extract, configure & compile memcached
• Extract configure & compile php extension

Compile Memcached

• Standard configure, make, make instal
• A few gotchas
• Memcached requires libevent (http://

www.monkey.org/~provos/libevent/)

• Even once you get libevent, you may need

a symlink to get memcached to see it.

• I recommend using a --prefix

Considerations

• For testing / small needs, run it on your

web server and give it a few MB of RAM

• Connections are via TCP/IP, so it can run

anywhere, but obviously you’ll want to strive for minimal network overhead

• There is NO security, repeat, NO security,

so if you don’t run it on localhost, use some sort of firewall

Memcache PHP Extension

• Memcache (notice there is no D here

because we’re not talking about the daemon) is a PECL extension

• Either use the “pecl install” feature or

download the source code and compile it yourself (then copy to ext/ folder and add to php.ini)

So Now What?

• Understand what memcached will and will

not do for you

• Understand what and when you should

cache

• Learn how to use the functions provided by

the PHP extension

What Memcached will not do:

• Tell you what is stored in it (list keys)
• Allow you to wildcard delete keys
• Cache very large items effectively
• native failover
• write contents to disk (planned)

What Memcached will do:

• Expire things automatically if you set a TTL
• Expire things when it runs out of space

(first in - first out)

• Tell you general stats (# connections, bytes

used, etc)

• Persistent connections
• Let you flush all the current keys

What should[n’t] you cache?

• The more specific a “question” you can ask of the cache,

the more benefit you will get

• Don’t attempt to cache mysql result sets (many

reasons...)

• Caching objects or arrays that have had computational

work done on them is good

• Caching snippets of HTML/XML is better
• Prevailing wisdom is that objects in cache should be less

(way less) than 1MB

How to know what’s cached?

• Create an index in a database table
• Create an index in memcache...
• Don’t care, just trust memcache_get() to

return false and handle it appropriately

Premature Optimization

• Don’t cache just because it sounds neat
• Fix your database schema & algorithms first
• If a script is too slow to run in your test

environment, caching is not a long term solution for you

So how fast is it?

• It’s all relative to how much processing you

have to do between a database (or other data source) and a user, but this demo shows between 12x and 40x faster than re- processing every time