Installation and use of php-Memcached

1. Introduction and installation

memcached is a high-performance distributed memory object caching system, which is usually used to reduce database loading pressure to improve the response speed of dynamic web applications.

This extension uses the API provided by the libmemcached library to interact with the memcached server. It also provides a session handler (memcached).

For the installation of memcached, please refer to this article: Installation and configuration of memcached in Ubuntu.

Before installing the PHP extension memcached, you need to install libmemcached. libmemcached is the C/C++ local client library of memcached.

Before installing libmemcached, you must first install libcloog-ppl0, otherwise an error will occur during the compilation and installation process:

sudo apt-get install libcloog-ppl0

Then download the required libmemcached source code installation package from here http://libmemcached.org/libMemcached.html, and unzip it to Specify the directory, enter the directory, and then execute the following command:

./configure --prefix=/usr/local/libmemcached
make
sudo make install

Then you can install the memcached extension of php. Download the required source code installation package from here: http://pecl.php.net/package/memcached , decompress to the specified directory, enter the directory, and then execute the following instructions:

phpize
./configure --with-php-config=/usr/local/php/bin/php-config --with-libmemcached-dir=/usr/local/libmemcached
make
sudo make install

An error may be reported during the installation process:

未知类型名称：memcached_server_instance_st

causing make to fail. The solution is as follows:

Find this file in the memcached extension decompression directory: php_libmemcached_compat.h, then add the following line in it

typedef const struct memcached_server_st *memcached_server_instance_st;

make again, and it will be OK.

After the installation is successful, add extension=memcacached in php.ini, then restart apache, check phpinfo, and see the following section

to prove that the installation is successful.

2. Timeout

Some storage commands will contain an expiration value (related to an element or a client operation request) when sent to the server. For all such uses, the actual value sent can be a Unix timestamp (an integer number of seconds since January 1, 1970 until the expiration time), or a number in seconds from now. In the latter case, this number of seconds cannot exceed 60 × 60 × 24 × 30 (seconds in 30 days); if the invalid value is greater than this value, the server will treat it as a real Unix timestamp. Not an offset from the current time.

If the expiration value is set to 0 (default), this element will never expire (but it may be deleted by the server to allocate space for other new elements).

3. Callbacks

1. Result callbacks

Result callbacks method is called once for each element in the result set after obtaining the element through the Memcached::getDelayed() or Memcached::getDelayedBykey() method. The callback function can receive a Memcached object and element information described by an array. This callback function does not need to return any information.

Example #1 Result callback example

<?php
    $m = new Memcached();
    $m->addServer(&#39;localhost&#39;, 11211);
    $items = array(
        &#39;key1&#39; => &#39;value1&#39;,
        &#39;key2&#39; => &#39;value2&#39;,
        &#39;key3&#39; => &#39;value3&#39;
    );
    $m->setMulti($items);
    $m->getDelayed(array(&#39;key1&#39;, &#39;key3&#39;), true, &#39;result_cb&#39;);
    function result_cb($memc, $item)
    {
        var_dump($item);
    }
?>

The output of the above routine is similar to:

array(3) {
  ["key"]=> string(4) "key1"
  ["value"]=> string(6) "value1"
  ["cas"]=> float(49)
}
array(3) {
  ["key"]=> string(4) "key3"
  ["value"]=> string(6) "value3"
  ["cas"]=> float(50)
}

2. Read through cache callback

The read through cache callback is called when an element is not retrieved from the server. This callback function will receive three parameters: the Memcached object, the requested key, and a value variable passed by reference. This callback function is responsible for deciding to set a default value when the key has no value by returning true or false. If the callback returns true, Memcached will store the value stored in the "outgoing parameter" (the value variable passed by reference) to the memcached server and return it to the original calling function. Only Memcached::get() and Memcached::getByKey() support this type of callback, because the Memcache protocol does not support providing information about unretrieved keys when requesting multiple keys.

Example #2 Read through the callback example

<?php
    $m = new Memcached();
    $m->addServer(&#39;localhost&#39;, 11211);
    $profile_info = $m->get(&#39;user:&#39;.$user_id, &#39;user_info_cb&#39;);
    function user_info_cb($memc, $key, &$value)
    {
        $user_id = substr($key, 5);
        /* 从数据库读取个人信息 */
        /* ... */
        $value = $profile_info;
        return true;
    }
?>

4. Sessions support

memcached provides a custom session processor that can be used to store user session data to the memcached server. A completely separate memcached instance will be used internally, so you can set up a different server pool if needed. Session keys are stored under the prefix memc.sess.key., so please be aware of this if you are using the same server pool for sessions and normal caching. Annotation: Another reason why the session is separated from the normal cache is that when the normal cache fills up the memcached server, your session may be kicked out of the cache, causing the user to be disconnected inexplicably.

session.save_handler is set to memcached to enable memcached's session processor. session.save_path defines a comma-separated hostname:port style session cache server pool, for example: "sess1:11211, sess2:11211".

5. Memcached class

represents the connection to the memcached service cluster.

Memcached::add — Add an element to a new key

Memcached::addByKey — Add an element to a new key on the specified server

Memcached::addServer — Add a server to the server pool

Memcached::addServers — Add multiple servers to the server pool

Memcached::append — Append data to existing elements

Memcached::appendByKey — Append data to existing elements on the specified server

Memcached:: cas — Compare and exchange values ​​

Memcached::casByKey — Compare and exchange values ​​on the specified server

Memcached::__construct — Create a Memcached instance

Memcached::decrement — Decrement the value of a numeric element

Memcached:: decrementByKey — Decrement numeric item's value, stored on a specific server

Memcached::delete — Delete an element

Memcached::deleteByKey — Delete an element from the specified server

Memcached::deleteMulti — Delete multiple items

Memcached: :deleteMultiByKey — Delete multiple items from a specific server

Memcached::fetch — Fetch the next result

Memcached::fetchAll — Fetch all remaining results

Memcached::flush — Invalidate all elements in the cache

Memcached::get — Retrieve an element

Memcached::getAllKeys — Gets the keys stored on all the servers

Memcached::getByKey — Retrieve an element from a specific server

Memcached::getDelayed — Request multiple elements

Memcached ::getDelayedByKey — Request multiple elements from a specified server

Memcached::getMulti — Retrieve multiple elements

Memcached::getMultiByKey — Retrieve multiple elements from a specific server

Memcached::getOption — Get the option value of Memcached

Memcached::getResultCode — Returns the result code of the last operation

Memcached::getResultMessage — Returns the result description message of the last operation

Memcached::getServerByKey — Gets the server information mapped by a key

Memcached::getServerList — Get the server list in the server pool

Memcached::getStats — Get the statistical information of the server pool

Memcached::getVersion — Get the version information of all servers in the server pool

Memcached::increment — Increase the value of the numerical element

Memcached::incrementByKey — Increment numeric item's value, stored on a specific server

Memcached::isPersistent — Check if a persistent connection to memcache is being used

Memcached::isPristine — Check if the instance was recently created

Memcached ::prepend — Prepend data to an existing item on a specific server

Memcached::prependByKey — Prepend data to an existing item on a specific server

Memcached::quit — Close any open connections

Memcached::replace — Replace Elements existing under key

Memcached::replaceByKey — Replace the item under an existing key on a specific server

Memcached::resetServerList — Clears all servers from the server list

Memcached::set — Store an element

Memcached ::setByKey — Store an item on a specific server

Memcached::setMulti — Store multiple elements

Memcached::setMultiByKey — Store multiple items on a specific server

Memcached::setOption — Set a memcached option

Memcached ::setOptions — Set Memcached options

Memcached::setSaslAuthData — Set the credentials to use for authentication

Memcached::touch — Set a new expiration on an item

Memcached::touchByKey — Set a new expiration on an item on a specific server