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Manual Reference Pages  -  CACHE::MEMCACHED (3)

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Cache::Memcached - client library for memcached (memory cache daemon)



  use Cache::Memcached;

  $memd = new Cache::Memcached {
    servers => [ "", "", "/var/sock/memcached",
                   "", [ "", 3 ] ],
    debug => 0,
    compress_threshold => 10_000,

  $memd->set("my_key", "Some value");
  $memd->set("object_key", { complex => [ "object", 2, 4 ]});

  $val = $memd->get("my_key");
  $val = $memd->get("object_key");
  if ($val) { print $val->{complex}->[2]; }

  $memd->incr("key", 2);


This is the Perl API for memcached, a distributed memory cache daemon. More information is available at:


new Takes one parameter, a hashref of options. The most important key is servers, but that can also be set later with the set_servers method. The servers must be an arrayref of hosts, each of which is either a scalar of the form or an arrayref of the former and an integer weight value. (The default weight if unspecified is 1.) It’s recommended that weight values be kept as low as possible, as this module currently allocates memory for bucket distribution proportional to the total host weights.

Use compress_threshold to set a compression threshold, in bytes. Values larger than this threshold will be compressed by set and decompressed by get.

Use no_rehash to disable finding a new memcached server when one goes down. Your application may or may not need this, depending on your expirations and key usage.

Use readonly to disable writes to backend memcached servers. Only get and get_multi will work. This is useful in bizarre debug and profiling cases only.

Use namespace to prefix all keys with the provided namespace value. That is, if you set namespace to app1: and later do a set of foo to bar, memcached is actually seeing you set app1:foo to bar.

Use connect_timeout and select_timeout to set connection and polling timeouts. The connect_timeout defaults to .25 second, and the select_timeout defaults to 1 second.

The other useful key is debug, which when set to true will produce diagnostics on STDERR.


set_servers Sets the server list this module distributes key gets and sets between. The format is an arrayref of identical form as described in the new constructor.
set_debug Sets the debug flag. See new constructor for more information.
set_readonly Sets the readonly flag. See new constructor for more information.
set_norehash Sets the no_rehash flag. See new constructor for more information.
set_compress_threshold Sets the compression threshold. See new constructor for more information.
set_connect_timeout Sets the connect timeout. See new constructor for more information.
set_select_timeout Sets the select timeout. See new constructor for more information.
enable_compress Temporarily enable or disable compression. Has no effect if compress_threshold isn’t set, but has an overriding effect if it is.
get my $val = $memd->get($key);

Retrieves a key from the memcache. Returns the value (automatically thawed with Storable, if necessary) or undef.

The $key can optionally be an arrayref, with the first element being the hash value, if you want to avoid making this module calculate a hash value. You may prefer, for example, to keep all of a given user’s objects on the same memcache server, so you could use the user’s unique id as the hash value.

get_multi my $hashref = $memd->get_multi(@keys);

Retrieves multiple keys from the memcache doing just one query. Returns a hashref of key/value pairs that were available.

This method is recommended over regular ’get’ as it lowers the number of total packets flying around your network, reducing total latency, since your app doesn’t have to wait for each round-trip of ’get’ before sending the next one.

set $memd->set($key, $value[, $exptime]);

Unconditionally sets a key to a given value in the memcache. Returns true if it was stored successfully.

The $key can optionally be an arrayref, with the first element being the hash value, as described above.

The $exptime (expiration time) defaults to never if unspecified. If you want the key to expire in memcached, pass an integer $exptime. If value is less than 60*60*24*30 (30 days), time is assumed to be relative from the present. If larger, it’s considered an absolute Unix time.

add $memd->add($key, $value[, $exptime]);

Like set, but only stores in memcache if the key doesn’t already exist.

replace $memd->replace($key, $value[, $exptime]);

Like set, but only stores in memcache if the key already exists. The opposite of add.

delete $memd->delete($key[, $time]);

Deletes a key. You may optionally provide an integer time value (in seconds) to tell the memcached server to block new writes to this key for that many seconds. (Sometimes useful as a hacky means to prevent races.) Returns true if key was found and deleted, and false otherwise.

You may also use the alternate method name <B>removeB>, so Cache::Memcached looks like the Cache::Cache API.

incr $memd->incr($key[, $value]);

Sends a command to the server to atomically increment the value for $key by $value, or by 1 if $value is undefined. Returns undef if $key doesn’t exist on server, otherwise it returns the new value after incrementing. Value should be zero or greater. Overflow on server is not checked. Be aware of values approaching 2**32. See decr.

decr $memd->decr($key[, $value]);

Like incr, but decrements. Unlike incr, underflow is checked and new values are capped at 0. If server value is 1, a decrement of 2 returns 0, not -1.

stats $memd->stats([$keys]);

Returns a hashref of statistical data regarding the memcache server(s), the $memd object, or both. $keys can be an arrayref of keys wanted, a single key wanted, or absent (in which case the default value is malloc, sizes, self, and the empty string). These keys are the values passed to the ’stats’ command issued to the memcached server(s), except for ’self’ which is internal to the $memd object. Allowed values are:
misc The stats returned by a ’stats’ command: pid, uptime, version, bytes, get_hits, etc.
malloc The stats returned by a ’stats malloc’: total_alloc, arena_size, etc.
sizes The stats returned by a ’stats sizes’.
self The stats for the $memd object itself (a copy of $memd->{’stats’}).
maps The stats returned by a ’stats maps’.
cachedump The stats returned by a ’stats cachedump’.
slabs The stats returned by a ’stats slabs’.
items The stats returned by a ’stats items’.

disconnect_all $memd->disconnect_all;

Closes all cached sockets to all memcached servers. You must do this if your program forks and the parent has used this module at all. Otherwise the children will try to use cached sockets and they’ll fight (as children do) and garble the client/server protocol.

flush_all $memd->flush_all;

Runs the memcached flush_all command on all configured hosts, emptying all their caches. (or rather, invalidating all items in the caches in an O(1) operation...) Running stats will still show the item existing, they’re just be non-existent and lazily destroyed next time you try to detch any of them.


When a server goes down, this module does detect it, and re-hashes the request to the remaining servers, but the way it does it isn’t very clean. The result may be that it gives up during its rehashing and refuses to get/set something it could’ve, had it been done right.


This module is Copyright (c) 2003 Brad Fitzpatrick. All rights reserved.

You may distribute under the terms of either the GNU General Public License or the Artistic License, as specified in the Perl README file.




See the memcached website:


Brad Fitzpatrick <>

Anatoly Vorobey <>

Brad Whitaker <>

Jamie McCarthy <>

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perl v5.20.3 CACHE::MEMCACHED (3) 2012-05-19

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