Cache::File(3) User Contributed Perl Documentation Cache::File(3)NAMECache::File - Filesystem based implementation of the Cache interface
SYNOPSIS
use Cache::File;
my $cache = Cache::File->new( cache_root => '/tmp/mycache',
default_expires => '600 sec' );
See Cache for the usage synopsis.
DESCRIPTION
The Cache::File class implements the Cache interface. This cache
stores data in the filesystem so that it can be shared between
processes and persists between process invocations.
CONSTRUCTOR
my $cache = Cache::File->new( %options )
The constructor takes cache properties as named arguments, for example:
my $cache = Cache::File->new( cache_root => '/tmp/mycache',
lock_level => Cache::File::LOCK_LOCAL(),
default_expires => '600 sec' );
Note that you MUST provide a cache_root property.
See 'PROPERTIES' below and in the Cache documentation for a list of all
available properties that can be set.
METHODS
See 'Cache' for the API documentation.
PROPERTIESCache::File adds the following properties in addition to those
discussed in the 'Cache' documentation.
cache_root
Used to specify the location of the cache store directory. All
methods will work ONLY data stored within this directory. This
parameter is REQUIRED when creating a Cache::File instance.
my $ns = $c->cache_root();
cache_depth
The number of subdirectories deep to store cache entires. This
should be large enough that no cache directory has more than a few
hundred object. Defaults to 2 unless explicitly set.
my $depth = $c->cache_depth();
cache_umask
Specifies the umask to use when creating entries in the cache
directory. By default the umask is '077', indicating that only the
same user may access the cache files.
my $umask = $c->cache_umask();
lock_level
Specify the level of locking to be used. There are three different
levels available:
Cache::File::LOCK_NONE()
No locking is performed. Useful when you can guarantee only
one process will be accessing the cache at a time.
Cache::File::LOCK_LOCAL()
Locking is performed, but it is not suitable for use over NFS
filesystems. However it is more efficient.
Cache::File::LOCK_NFS()
Locking is performed in a way that is suitable for use on NFS
filesystems.
my $level = $c->cache_lock_level();
CAVEATS
There are a couple of caveats in the current implementation of
Cache::File. None of these will present a problem in using the class,
it's more of a TODO list of things that could be done better.
external cache modification (and re-syncronization)
Cache::File maintains indexes of entries in the cache, including
the number of entries and the total size. Currently there is no
process of checking that the count or size are in syncronization
with the actual data on disk, and thus any modifications to the
cache store by another program (eg. a user shell) will result in an
inconsitency in the index. A better process would be for
Cache::File to resyncronize at an appropriate time (eg whenever the
size or count is initially requested - this would only need happen
once per instance). This resyncronization would involve
calculating the total size and count as well as checking that
entries in the index accurately reflect what is on the disk (and
removing any entries that have dissapeared or adding any new ones).
index efficiency
Currently Berkeley DB's are used for indexes of expiry time, last
use and entry age. They use the BTREE variant in order to
implement a heap (see Cache::File::Heap). This is probably not the
most efficient format and having 3 separate index files adds
overhead. These are also cross-referenced with a fourth index file
that uses a normal hash db and contains all these time stamps
(frozen together with the validity object to a single scalar via
Storable) indexed by key. Needless to say, all this could be done
more efficiently - probably by using a single index in a custom
format.
locking efficiency
Currently LOCK_LOCAL is not implemented (if uses the same code as
LOCK_NFS).
There are two points of locking in Cache::File, index locking and
entry locking. The index locking is always exclusive and the lock
is required briefly during most operations. The entry locking is
either shared or exclusive and is also required during most
operations. When locking is enabled, File::NFSLock is used to
provide the locking for both situations. This is not overly
efficient, especially as the entry lock is only ever grabbed whilst
the index lock is held.
SEE ALSO
Cache
AUTHOR
Chris Leishman <chris@leishman.org>
Based on work by DeWitt Clinton <dewitt@unto.net>
COPYRIGHT
Copyright (C) 2003-2006 Chris Leishman. All Rights Reserved.
This module is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
KIND, either expressed or implied. This program is free software; you
can redistribute or modify it under the same terms as Perl itself.
$Id: File.pm,v 1.7 2006/01/31 15:23:58 caleishm Exp $
POD ERRORS
Hey! The above document had some coding errors, which are explained
below:
Around line 588:
You forgot a '=back' before '=head1'
perl v5.14.1 2006-01-31 Cache::File(3)
