3 This file contains installation instructions for the 8.x-1.x version of the
4 Drupal Memcache module. Configuration differs between 8.x and 7.x versions
5 of the module, so be sure to follow the 7.x instructions if you are configuring
6 the 7.x-1.x version of this module!
11 - Availability of a memcached daemon: http://memcached.org/
12 - One of the two PECL memcache packages:
13 - http://pecl.php.net/package/memcache (recommended)
14 - http://pecl.php.net/package/memcached
16 For more detailed instructions on installing a memcached daemon or either of the
17 memcache PECL extensions, please see the documentation online at
18 https://www.drupal.org/node/1131458 which includes links to external
19 walk-throughs for various operating systems.
23 These are the steps you need to take in order to use this software. Order
26 1. Make sure you have one of the PECL memcache packages installed.
27 2. Enable the memcache module.
28 You need to enable the module in Drupal before you can configure it to run
29 as the default backend. This is so Drupal knows where to find everything.
30 2. Edit settings.php to configure the servers, clusters and bins that memcache
31 is supposed to use. You do not need to set this if the only memcache backend
32 is localhost on port 11211. By default the main settings will be:
33 $settings['memcache']['servers'] = ['127.0.0.1:11211' => 'default'];
34 $settings['memcache']['bins'] = ['default' => 'default'];
35 $settings['memcache']['key_prefix'] = '';
36 7. Edit settings.php to make memcache the default cache class, for example:
37 $settings['cache']['default'] = 'cache.backend.memcache';
38 8. If you wish to arbitrarily send cache bins to memcache, then you can do the
39 following. E.g. for the cache_render bin:
40 $settings['cache']['bins']['render'] = 'cache.backend.memcache';
42 ## ADVANCED CONFIGURATION ##
44 ### Multiple memcache backends ###
46 $settings['memcache']['servers'] = [
47 '127.0.0.1:11211' => 'default', // Default host and port
48 '127.0.0.1:11212' => 'default', // Default host with port 11212
49 '127.0.0.2:11211' => 'default', // Default port, different IP
50 'server1.com:11211' => 'default', // Default port with hostname
51 'unix:///path/to/socket' => 'default', 'Unix socket'
54 ### Multiple servers, bins and clusters ###
56 $settings['memcache'] = [
58 'server1:port' => 'default',
59 'server2:port' => 'default',
60 'server3:port' => 'cluster1',
61 'serverN:port' => 'clusterN',
62 'unix:///path/to/socket' => 'clusterS',
65 'default' => 'default',
73 The bin/cluster/server model can be described as follows:
75 - Servers are memcached instances identified by host:port.
77 - Clusters are groups of servers that act as a memory pool. Each cluster can
78 contain one or more servers.
80 - Multiple bins can be assigned to a cluster.
82 - The default cluster is 'default'.
84 - If a bin can not be found it will map to 'default'.
86 ### Stampede Protection ###
88 Memcache includes stampede protection for rebuilding expired and invalid cache
89 items. To enable stampede protection, add the following config in settings.php:
91 $settings['memcache']['stampede_protection'] = TRUE;
93 To avoid lock stampedes, it is important that you enable the memcache lock
94 implementation when enabling stampede protection -- enabling stampede protection
95 without enabling the Memcache lock implementation can cause worse performance.
97 Only change the following values if you're sure you know what you're doing,
98 which requires reading the memcachie.inc code.
100 The value passed to lock_acquire, defaults to '15':
101 $conf['memcache_stampede_semaphore'] = 15;
103 The value passed to lock_wait, defaults to 5:
104 $conf['memcache_stampede_wait_time'] = 5;
106 The maximum number of calls to lock_wait() due to stampede protection during a
107 single request, defaults to 3:
108 $conf['memcache_stampede_wait_limit'] = 3;
110 When adjusting these variables, be aware that:
111 - there is unlikely to be a good use case for setting wait_time higher
112 than stampede_semaphore;
113 - wait_time * wait_limit is designed to default to a number less than
114 standard web server timeouts (i.e. 15 seconds vs. apache's default of
119 If you want to have multiple Drupal installations share memcached instances,
120 you need to include a unique prefix for each Drupal installation in the memcache
121 config in settings.php:
123 $settings['memcache']['key_prefix'] = 'something_unique';
125 ### Key Hash Algorithm
127 Note: if the length of your prefix + key + bin combine to be more than 250
128 characters, they will be automatically hashed. Memcache only supports key
129 lengths up to 250 bytes. You can optionally configure the hashing algorithm
130 used, however sha1 was selected as the default because it performs quickly with
133 $settings['memcache']['key_hash_algorithm'] = 'sha1';
135 Visit http://www.php.net/manual/en/function.hash-algos.php to learn more about
136 which hash algorithms are available.
138 ### Memcache Distribution ###
140 To use this module with multiple memcached servers, it is important that you set
141 the hash strategy to consistent. This is controlled in the PHP extension, not the
144 If using PECL memcache:
145 Edit /etc/php.d/memcache.ini (path may changed based on package/distribution) and
147 memcache.hash_strategy=consistent
149 You need to reload apache httpd after making that change.
151 If using PECL memcached:
152 Memcached options can be controlled in settings.php. Consistent distribution is
153 the default in this case but could be set using:
155 $setting['memcache']['options'] = [
156 Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT,
161 Locks have not yet been implemented using the memcache module.
163 ## TROUBLESHOOTING ##
167 Failed to set key: Failed to set key: cache_page-......
170 Upgrade your PECL library to PECL package (2.2.1) (or higher).
173 Zlib compression at the php.ini level and Memcache conflict.
174 See http://drupal.org/node/273824
178 A module offering a UI for memcache is included. It provides aggregated and
179 per-page statistics for memcache.
183 ### Memcached PECL Extension Support ###
185 We also support the Memcached PECL extension. This extension backends
186 to libmemcached and allows you to use some of the newer advanced features in
189 NOTE: It is important to realize that the memcache php.ini options do not impact
190 the memcached extension, this new extension doesn't read in options that way.
191 Instead, it takes options directly from Drupal. Because of this, you must
192 configure memcached in settings.php. Please look here for possible options:
194 https://secure.php.net/manual/en/memcached.constants.php
196 An example configuration block is below, this block also illustrates our
197 default options (selected through performance testing). These options will be
198 set unless overridden in settings.php.
200 $settings['memcache']['options'] = [
201 Memcached::OPT_COMPRESSION => FALSE,
202 Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT,
205 These are as follows:
207 * Turn off compression, as this takes more CPU cycles than it's worth for most
209 * Turn on consistent distribution, which allows you to add/remove servers
212 Other options you could experiment with:
213 + Memcached::OPT_BINARY_PROTOCOL => TRUE,
214 * This enables the Memcache binary protocol (only available in Memcached
215 1.4 and later). Note that some users have reported SLOWER performance
216 with this feature enabled. It should only be enabled on extremely high
217 traffic networks where memcache network traffic is a bottleneck.
218 Additional reading about the binary protocol:
219 https://raw.githubusercontent.com/memcached/old-wiki/master/MemcacheBinaryProtocol.wiki
220 Note: The information on the link above will eventually be ported to
221 the new wiki under https://github.com/memcached/memcached/wiki.
223 + Memcached::OPT_TCP_NODELAY => TRUE,
224 * This enables the no-delay feature for connecting sockets; it's been
225 reported that this can speed up the Binary protocol (see above). This
226 tells the TCP stack to send packets immediately and without waiting for
227 a full payload, reducing per-packet network latency (disabling "Nagling").