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README
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README
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Copyright (C) 2001-2006 DeWitt Clinton 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.
NAME
Cache::Cache
DESCRIPTION
The Cache modules are designed to assist a developer in persisting
data for a specified period of time. Often these modules are used
in web applications to store data locally to save repeated and
redundant expensive calls to remote machines or databases. People
have also been known to use Cache::Cache for its straightforward
interface in sharing data between runs of an application or
invocations of a CGI-style script or simply as an easy to use
abstraction of the filesystem or shared memory.
The Cache package provides Cache::Cache, a generic interface
for creating persistent data stores. This interface is implemented
by the Cache::MemoryCache, Cache::SharedMemoryCache, Cache::FileCache,
Cache::SizeAwareFileCache, Cache::SizeAwareMemoryCache, and
Cache::SizeAwareSharedMemoryCache classes.
This work aggregates and extends the obsolete File::Cache and
IPC::Cache projects.
CACHE::CACHE VERSUS CHI
Cache::Cache is in wide use and very stable, but has not changed in years
and is no longer actively developed.
L<CHI|CHI> is the successor to Cache::Cache. It adheres to the basic
Cache::Cache API but adds new features and drivers (e.g. FastMmap and
Memcached), improves performance, and addresses limitations in the
Cache::Cache implementation. The authors recommend the use of CHI going forward.
Questions about Cache::Cache and CHI may be directed to the perl-cache
mailing list at http://groups.google.com/group/perl-cache-discuss.
REQUIREMENTS
Digest::SHA1
Error
File::Spec
File::Path
Storable
OPTIONAL
IPC::ShareLite
INSTALLATION
perl Makefile.PL
make
make test
make install
USAGE
First, choose the best type of cache implementation for your needs.
The simplest cache is the MemoryCache, which is suitable for
applications that are serving multiple sequential requests, and
wish to avoid making redundant expensive queries, such as an
Apache/mod_perl application talking to a database. If you wish to
share that data between processes, then perhaps the
SharedMemoryCache is appropriate, although its behavior is tightly
bound to the underlying IPC mechanism, which varies from system to
system, and is unsuitable for large objects or large numbers of
objects. When the SharedMemoryCache is not acceptable, then
FileCache offers all of the same functionality with similar
performance metrics, and it is not limited in terms of the number of
objects or their size. If you wish to maintain a strict limit on
the size of a file system based cache, then the SizeAwareFileCache
is the way to go. Similarly, the SizeAwareMemoryCache and the
SizeAwareSharedMemoryCache add size management functionality
to the MemoryCache and SharedMemoryCache classes respectively.
Using a cache is simple. Here is some sample code for instantiating
and using a file system based cache.
use Cache::FileCache;
my $cache = new Cache::FileCache( );
my $customer = $cache->get( $name );
if ( not defined $customer )
{
$customer = get_customer_from_db( $name );
$cache->set( $name, $customer, "10 minutes" );
}
return $customer;
Please refer to the perldoc for Cache::Cache and the related
implementations for complete documentation.
INCOMPATIBLE CHANGES
Cache::Cache 0.99 contains the following incompatible changes:
* Error::Simple is thrown on exceptions
* the get_identifiers method has been deprecated in favor of the
get_keys method
* the internal format of object in a FileCache has been modified,
necessitating a clearing of the cache while upgrading (make test
does this for the standard cache root)
Also note that Storable is not forward compatible between all
releases. That is, older versions of the Cache will not always
be able to read objects written by newer versions. This is
unlikely to ever be an issue in production scenarios.
ON LOCKING:
The FileCache backend uses an temp file and an atomic rename to
avoid requiring a lock during the write. This has been demonstrated
to be safe across all platforms to date.
The MemoryCache backend relies on Perl's atomic write to a hash to
ensure that a lock is not required.
The SharedMemoryCache backend uses ShareLite's locking mechanism
for safety during the write.
SEE ALSO
The project homepage at http://perl-cache.googlecode.com/.
The discussion list at http://groups.google.com/group/perl-cache-discuss.
The CHI project.
AUTHOR
Original author: DeWitt Clinton <dewitt@unto.net>
Copyright (C) 2001-2009 DeWitt Clinton