WWR - Railsplugin: Memcache Client Extensions

Memcache Client Extensions

=MemCacheClient Extensions

About

The memcache-client_extensions plugins adds three new commands to the memcache client API:

1. get_multi : retrieve more than 1 key in parallel 2. stats : retrieve server performance and utilization statistics 3. flush_all : empty all information stored in memcached

Installation

1. This plugin requires that the memcache-client gem is installed. # gem install memcache-client

2. Install the plugin or the gem $ script/plugin install svn://rubyforge.org/var/svn/zventstools/projects/memcache-client_extensions - OR - # gem install memcache-client_extensions

get_multi

Retrieve multiple values from memcached in parallel, if possible. The memcached protocol supports the ability to retrieve multiple keys in a single request. Pass in an array of keys to this method and it will: a. map the key to the appropriate memcached server b. send a single request to each server that has one or more key values

Returns a hash of values.

CACHE[“a”] = 1 => 1 CACHE[“b”] = 2 => 2 CACHE.get_multi([“a”,”b”]) => {“a”=>1, “b”=>2}

Here’s a benchmark showing the speedup:

CACHE[“a”] = 1 CACHE[“b”] = 2 CACHE[“c”] = 3 CACHE[“d”] = 4 keys = [“a”,”b”,”c”,”d”,”e”] Benchmark.bm do |x| x.report { for i in 1..1000; keys.each{|k| CACHE.get(k);} end } x.report { for i in 1..1000; CACHE.get_multi(keys); end } end

returns: user system total real 0.180000 0.130000 0.310000 ( 0.459418) 0.200000 0.030000 0.230000 ( 0.269632)

There’s a fair amount of non-DRY between get_multi and get (and threadsafe_cache_get/multi_threadsafe_cache_get and cache_get/multi_cache_get for that matter) but I think it’s worth it since the extra overhead to handle multiple return values is unneeded for a single-key get (which is by far the most common case).

stats

The stats method returns statistics for each memcached server. An explanation of the statistics can be found in the memcached docs: http://cvs.danga.com/browse.cgi/wcmtools/memcached/doc/protocol.txt?rev=HEAD&content-type=text/plain

Example: >> CACHE.stats => {“localhost:11211”=>{“pid”=>”20188”, “bytes”=>”4718”, “connection_structures”=>”4”, “time”=>”1162278121”, “pointer_size”=>”32”, “limit_maxbytes”=>”67108864”, “version”=>”1.2.0”, “cmd_get”=>”14532”, “cmd_set”=>”32”, “bytes_written”=>”432583”, “uptime”=>”1557”, “curr_items”=>”4”, “curr_connections”=>”3”, “total_connections”=>”19”, “get_misses”=>”0”, “rusage_user”=>”0.119981”, “rusage_system”=>”0.313952”, “total_items”=>”32”, “get_hits”=>”14532”, “bytes_read”=>”190619”}}

flush_all

The flush_all method empties all cache namespaces on all memcached servers. This method is very useful for testing your code with memcached since you normally want to reset the cache to a known (empty) state at the beginning of each test.

Bugs, Code and Contributing

There’s a RubyForge project set up at:

http://rubyforge.org/projects/zventstools/

Anonymous SVN access:

$ svn checkout svn://rubyforge.org/var/svn/zventstools

Author: Tyler Kovacs (tyler dot kovacs at gmail dot com)