# phpman > man > Cache::SharedMemoryCache(3pm)

## NAME
    [Cache::SharedMemoryCache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ASharedMemoryCache/markdown) -- extends the MemoryCache.

## DESCRIPTION
    The SharedMemoryCache extends the MemoryCache class and binds the data store to shared memory so
    that separate process can use the same cache.

    The official recommendation is now to use FileCache instead of SharedMemoryCache. The reasons
    for this include:

    1) FileCache provides equal or better performance in all cases that we've been able to test.
    This is due to all modern OS's ability to buffer and cache file system accesses very well.

    2) FileCache has no real limits on cached object size or the number of cached objects, whereas
    the SharedMemoryCache has limits, and rather low ones at that.

    3) FileCache works well on every OS, whereas the SharedMemoryCache works only on systems that
    support [IPC::ShareLite](https://www.chedong.com/phpMan.php/perldoc/IPC%3A%3AShareLite/markdown). And [IPC::ShareLite](https://www.chedong.com/phpMan.php/perldoc/IPC%3A%3AShareLite/markdown) is an impressive effort -- but think about how hard
    it is to get shared memory working properly on *one* system. Now imagine writing a wrapper
    around shared memory for many operating systems.

## SYNOPSIS
      use [Cache::SharedMemoryCache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ASharedMemoryCache/markdown);

      my %cache_options_= ( 'namespace' => 'MyNamespace',
                            'default_expires_in' => 600 );

      my $shared_memory_cache =
        new [Cache::SharedMemoryCache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ASharedMemoryCache/markdown)( \%cache_options ) or
          croak( "Couldn't instantiate SharedMemoryCache" );

## METHODS
    See [Cache::Cache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ACache/markdown) for the API documentation.

## OPTIONS
    See [Cache::Cache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ACache/markdown) for the standard options.

## PROPERTIES
    See [Cache::Cache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ACache/markdown) for the default properties.

## SEE ALSO
    [Cache::Cache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3ACache/markdown), [Cache::MemoryCache](https://www.chedong.com/phpMan.php/perldoc/Cache%3A%3AMemoryCache/markdown)

## AUTHOR
    Original author: DeWitt Clinton <<dewitt@unto.net>>

    Last author: $Author: dclinton $

    Copyright (C) 2001-2003 DeWitt Clinton