The Cache::Memcached
module provides a native
interface to the Memcache protocol, and provides support for the
core functions offered by memcached. You
should install the module using your hosts native package
management system. Alternatively, you can install the module
using CPAN
:
root-shell> perl -MCPAN -e 'install Cache::Memcached'
To use memcached from Perl through
Cache::Memcached
module, you first need to
create a new Cache::Memcached
object that
defines the list of servers and other parameters for the
connection. The only argument is a hash containing the options
for the cache interface. For example, to create a new instance
that uses three memcached servers:
use Cache::Memcached; my $cache = new Cache::Memcached { 'servers' => [ '192.168.0.100:11211', '192.168.0.101:11211', '192.168.0.102:11211', ], };
When using the Cache::Memcached
interface
with multiple servers, the API automatically performs certain
operations across all the servers in the group. For example,
getting statistical information through
Cache::Memcached
returns a hash that
contains data on a host by host basis, as well as generalized
statistics for all the servers in the group.
You can set additional properties on the cache object instance when it is created by specifying the option as part of the option hash. Alternatively, you can use a corresponding method on the instance:
servers
or method
set_servers()
— specifies the list
of the servers to be used. The servers list should be a
reference to an array of servers, with each element as the
address and port number combination (separated by a colon).
You can also specify a local connection through a UNIX
socket (for example
/tmp/sock/memcached
). You can also
specify the server with a weight (indicating how much more
frequently the server should be used during hashing) by
specifying an array reference with the
memcached server instance and a weight
number. Higher numbers give higher priority.
compress_threshold
or method
set_compress_threshold()
— specifies
the threshold when values are compressed. Values larger than
the specified number are automatically compressed (using
zlib
) during storage and retrieval.
no_rehash
or method
set_norehash()
— disables finding a
new server if the original choice is unavailable.
readonly
or method
set_readonly()
— disables writes to
the memcached servers.
Once the Cache::Memcached
object instance has
been configured you can use the set()
and
get()
methods to store and retrieve
information from the memcached servers.
Objects stored in the cache are automatically serialized and
deserialized using the Storable
module.
The Cache::Memcached
interface supports the
following methods for storing/retrieving data, and relate to the
generic methods as shown in the table.
Cache::Memcached Function |
Equivalent to |
---|---|
get() |
Generic get()
|
get_multi(keys) |
Gets multiple keys from memcache using just one
query. Returns a hash reference of key/value pairs. |
set() |
Generic set()
|
add() |
Generic add()
|
replace() |
Generic replace()
|
delete() |
Generic delete()
|
incr() |
Generic incr()
|
decr() |
Generic decr()
|
Below is a complete example for using
memcached with Perl and the
Cache::Memcached
module:
root-shell>!/usr/bin/perl use Cache::Memcached; use DBI; use Data::Dumper; # Configure the memcached server my $cache = new Cache::Memcached { 'servers' => [ 'localhost:11211', ], }; # Get the film name from the command line # memcached keys must not contain spaces, so create # a key name by replacing spaces with underscores my $filmname = shift or die "Must specify the film name\n"; my $filmkey = $filmname; $filmkey =~ s/ /_/; # Load the data from the cache my $filmdata = $cache->get($filmkey); # If the data wasn't in the cache, then we load it from the database if (!defined($filmdata)) { $filmdata = load_filmdata($filmname); if (defined($filmdata)) { # Set the data into the cache, using the key if ($cache->set($filmkey,$filmdata)) { print STDERR "Film data loaded from database and cached\n"; } else { print STDERR "Couldn't store to cache\n"; } } else { die "Couldn't find $filmname\n"; } } else { print STDERR "Film data loaded from Memcached\n"; } sub load_filmdata { my ($filmname) = @_; my $dsn = "DBI:mysql:database=sakila;host=localhost;port=3306"; $dbh = DBI->connect($dsn, 'sakila','password'); my ($filmbase) = $dbh->selectrow_hashref(sprintf('select * from film where title = %s', $dbh->quote($filmname))); if (!defined($filmname)) { return (undef); } $filmbase->{stars} = $dbh->selectall_arrayref(sprintf('select concat(first_name," ",last_name) ' . 'from film_actor left join (actor) ' . 'on (film_actor.actor_id = actor.actor_id) ' . ' where film_id=%s', $dbh->quote($filmbase->{film_id}))); return($filmbase); }
The example uses the Sakila database, obtaining film data from the database and writing a composite record of the film and actors to memcache. When calling it for a film does not exist, you should get this result:
shell> memcached-sakila.pl "ROCK INSTINCT" Film data loaded from database and cached
When accessing a film that has already been added to the cache:
shell> memcached-sakila.pl "ROCK INSTINCT" Film data loaded from Memcached
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