MemcacheShim

MemcacheShim is a backfill that provides compatability for code that requires
the Memcache class, but is running on a server to a server that does not
have it installed and does have Memcached.

It exists because the dotdeb repos for PHP7 do not have php7.0-memcache, but
they do have PHP7.0-memcached. In all cases, it is better to use php-memcache
if it is available.

Structure

-- memcacheshim
  +-- README.md: this README file
  +-- memcacheshim.class.php: the shim class that maps memcache functions to memcached
  +-- memcacheshim.functions.php: backfills for the procedural memcache_* functions
  +-- memcacheshim.php: the file that bootstraps and configures the shim

Usage

require 'path/to/memcacheshim/memcacheshim.php';

Configuration

Configuration is handled with a couple of constants and a function that you.
can optionally define. Set them before including the bootstrap file.

Constants:

• MEMCACHESHIM_CLASS: Alias the MemacheShim class to Memcache. Default true
• MEMCACHESHIM_FUNCTIONS: create the memcache_* functions using the
  MemcacheShim class. Default true.
• MEMCACHESHIM_PERSISTENT_ID: If you wish to use persistent connections, set
  this to a unique string. Default false.

Function: create a function named "memcacheshim_options" that returns an array
of key => value pairs that will be passed to the Memcached object(s) via
Memcached::setOption(). For example:

function memcacheshim_options()
{
    return array(
        Memcached::OPT_PREFIX_KEY => "widgets",
    );
}

Limitations

Due to differences in the way that Memcache and Memcached work, there are some
behaviours and options that will not work with this shim. These include:

• advanced server pool management: Although the shim contains functions for
  adding and changing server options, in practice they only add. You won't be
  able to do anything advanced in this regard. This affects the methods
  Memcache::addServer and Memcache::setServerParams. Further, getting server
  connection statuses from Memcache::connect and Memcache::pconnect is sketchy
  at best.

• Server-by-server persistent connections : Memcache allows you to set
  persistent connections on a server-by-server basis, in Memcached it is a
  object-level setting. For the MemcacheShim, it is a global setting.

• Variable-by-variable options: the get/set/replace methods for memcached allow
  you to set compression variables on a variable-by-variable basis with
  a flags option. This is an object-level parameter in Memcached, and a global
  option in the MemcacheShim.

• Mixed environments hitting the same Memcached server. There are known issues
  mixing Memcache and Memcached. You need to use one or the other to connect to
  the Memcached server. See http://php.net/manual/en/book.memcached.php#115667