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NAME
Memcached::libmemcached - Thin fast full interface to the libmemcached client API
VERSION
Version 0.1402 (with libmemcached-0.14 embedded)
SYNOPSIS
use Memcached::libmemcached;
$memc = memcached_create();
memcached_server_add($memc, "localhost");
memcached_set($memc, $key, $value);
$value = memcached_get($memc, $key);DESCRIPTION
Memcached::libmemcached is a very thin, highly efficient, wrapper around the libmemcached library.
It gives full access to the rich functionality offered by libmemcached. libmemcached is fast, light on memory usage, thread safe, and provide full access to server side methods.
- Synchronous and Asynchronous support.
- TCP and Unix Socket protocols.
- A half dozen or so different hash algorithms.
- Implementations of the new cas, replace, and append operators.
- Man pages written up on entire API.
- Implements both modulo and consistent hashing solutions. (At the moment Memcached::libmemcached is very new and not all the functions in libmemcached have perl interfaces yet. We're focussing on the core infrastructure and the most common functions. It's usually trivial to add functions - just a few lines in libmemcached.xs, a few lines of documentation, and a few lines of testing. Volunteers welcome!)
The libmemcached library documentation (which is bundled with this module) serves as the primary reference for the functionality.
This documentation provides summary of the functions, along with any issues specific to this perl interface, and references to the documentation for the corresponding functions in the underlying library.
For more information on libmemcached, see http://tangent.org/552/libmemcached.html
CONVENTIONS
Terminology
The term "memcache" is used to refer to the memcached_st structure at the heart of the libmemcached library. We'll use $memc to represent this structure in perl code.
Function Names and Arguments
The function names in this module are exactly the same as the functions in the libmemcached library and documentation.
The function arguments are also the same as the libmemcached library and documentation, with two exceptions:
* There are no length arguments. Wherever the libmemcached documentation shows a length argument (input or output) the corresponding argument doesn't exist in the Perl API, because it's not needed.
* Some arguments are optional.
Many libmemcached function arguments are output values: the argument is the address of the value that the function will modify. For these the perl function will modify the argument directly if it can. For example, in this call:
$value = memcached_get($memc, $key, $flags, $rc);The $flags and $rc arguments are output values that are modified by the memcached_get() function.
See the "Type Mapping" section for the fine detail of how each argument type is handled.
Return Status
Most of the functions return an integer status value. This is shown as memcached_return in the libmemcached documentation.
In the perl interface this value is not returned directly. Instead a simple boolean is returned: true for 'success', defined but false for some 'unsuccessfull' conditions, and undef for all other cases (i.e., errors).
All the functions documented below return this simple boolean value unless otherwise indicated.
The actual memcached_return integer value, and corresponding error message, for the last libmemcached function call can be accessed via the "memcached_errstr" function.
EXPORTS
All the public functions in libmemcached are available for import.
All the public constants and enums in libmemcached are also available for import.
Exporter tags are defined for each enum. This allows you to import groups of constants easily. For example, to enable consistent hashing you could use:
use Memcached::libmemcached qw(:memcached_behavior :memcached_server_distribution);
memcached_behavior_set($memc, MEMCACHED_BEHAVIOR_DISTRIBUTION(), MEMCACHED_DISTRIBUTION_CONSISTENT());The Exporter module allows patterns in the import list, so to import all the functions, for example, you can use:
use Memcached::libmemcached qw(/^memcached/);FUNCTIONS
Functions For Managing Memcaches
memcached_create
my $memc = memcached_create();Creates and returns a 'memcache' that represents the state of communication with a set of memcached servers. See Memcached::libmemcached::memcached_create.
memcached_clone
my $memc = memcached_clone(undef, undef);XXX Not currently recommended for use. See Memcached::libmemcached::memcached_create.
memcached_free
memcached_free($memc); # voidFrees the memory associated with $memc. Your application will leak memory unless you call this. After calling it $memc must not be used. See Memcached::libmemcached::memcached_create.
memcached_server_push
memcached_server_push($memc, $server_list_object);Adds a list of servers to the libmemcached object. See Memcached::libmemcached::memcached_servers.
memcached_server_count
$server_count= memcached_server_count($memc);Returns a count of the number of servers associated with $memc. See Memcached::libmemcached::memcached_servers.
memcached_server_add
memcached_server_add($memc, $hostname, $port);Adds details of a single memcached server (accessed via TCP/IP) to $memc. See Memcached::libmemcached::memcached_servers.
memcached_server_add_unix_socket
memcached_server_add_unix_socket($memc, $socket_path);Adds details of a single memcached server (accessed via a UNIX domain socket) to $memc. See Memcached::libmemcached::memcached_servers.
memcached_behavior_set
memcached_behavior_set($memc, $option_key, $option_value);Changes the value of a particular option. See Memcached::libmemcached::memcached_behavior.
memcached_behavior_get
memcached_behavior_get($memc, $option_key);Get the value of a particular option. See Memcached::libmemcached::memcached_behavior.
memcached_verbosity
memcached_verbosity($memc, $verbosity)Modifies the "verbosity" of the associated memcached servers. See Memcached::libmemcached::memcached_verbosity.
memcached_flush
memcached_flush($memc, $expiration);Wipe clean the contents of associated memcached servers. See Memcached::libmemcached::memcached_flush.
memcached_quit
memcached_quit($memc);Disconnect from all currently connected servers and reset state. Not normally called explicitly. See Memcached::libmemcached::memcached_quit.
memcached_errstr
$errstr = memcached_errstr($memc);Returns the error message and code from the most recent call to any libmemcached function that returns a memcached_return, which most do.
The return value is a dualvar, like $!, which means it has separate numeric and string values. The numeric value is the memcached_return integer value, and the string value is the corresponding error message what memcached_strerror() would return.
As a special case, if the memcached_return is MEMCACHED_ERRNO, indicating a system call error, then the string returned by strerror() is appended.
Functions for Setting Values
See Memcached::libmemcached::memcached_set.
memcached_set
memcached_set($memc, $key, $value);
memcached_set($memc, $key, $value, $expiration, $flags);Set $value as the value of $key. $expiration and $flags are both optional and default to 0.
memcached_add
memcached_add($memc, $key, $value);
memcached_add($memc, $key, $value, $expiration, $flags);Like "memcached_set" except that an error is returned if $key is already stored in the server.
memcached_replace
memcached_replace($memc, $key, $value);
memcached_replace($memc, $key, $value, $expiration, $flags);Like "memcached_set" except that an error is returned if $key is not already error is returned.
memcached_prepend
memcached_prepend($memc, $key, $value);
memcached_prepend($memc, $key, $value, $expiration, $flags);Prepend $value to the value of $key. $key must already exist. $expiration and $flags are both optional and default to 0.
memcached_append
memcached_append($memc, $key, $value);
memcached_append($memc, $key, $value, $expiration, $flags);Append $value to the value of $key. $key must already exist. $expiration and $flags are both optional and default to 0.
memcached_cas
memcached_cas($memc, $key, $value, $expiration, $flags, $cas)Overwrites data in the server stored as $key as long as $cas still has the same value in the server.
Cas is still buggy in memached. Turning on support for it in libmemcached is optional. Please see memcached_behavior_set() for information on how to do this.
XXX and the memcached_result_cas() function isn't implemented yet so you can't get the $cas to use.
Functions for Fetching Values
See Memcached::libmemcached::memcached_get.
The memcached_fetch_result() and
memcached_get
$value = memcached_get($memc, $key);
$value = memcached_get($memc, $key, $flags, $rc);Get and return the value of $key. Returns undef on error.
Also updates $flags to the value of the flags stored with $value, and updates $rc with the return code.
memcached_mget
memcached_mget($memc, \@keys);
memcached_mget($memc, \%keys);Triggers the asynchronous fetching of multiple keys at once. For multiple key operations it is always faster to use this function. You must then use memcached_fetch() or memcached_fetch_result() to retrieve any keys found. No error is given on keys that are not found.
Instead of this function, you'd normally use "memcached_mget_into_hashref".
memcached_mget_into_hashref
memcached_mget_into_hashref($memc, $keys_ref, \%dest_hash);Combines memcached_mget() and a memcached_fetch() loop into a single highly efficient call.
Fetched values are stored in \%dest_hash, updating existing values or adding new ones as appropriate.
memcached_fetch
$value = memcached_fetch($memc, $key);
$value = memcached_fetch($memc, $key, $flag, $rc);Fetch the next $key and $value pair returned in response to a memcached_mget() call. Returns undef if there are no more values.
If $flag is given then it will be updated to whatever flags were stored with the value. If $rc is given then it will be updated to the return code.
This is similar to memcached_get except its fetching the results from the previous call to "memcached_mget" and $key is an output parameter instead of an input. Usually you'd just use "memcached_mget_into_hashref" instead.
Functions for Incrementing and Decrementing Values
memcached_increment
memcached_increment( $key, $offset, $new_value_out );Increments the integer value associated with $key by $offset and returns the new value in $new_value_out. See also Memcached::libmemcached::memcached_auto.
memcached_decrement
memcached_decrement( $key, $offset, $new_value_out );Decrements the integer value associated with $key by $offset and returns the new value in $new_value_out. See also Memcached::libmemcached::memcached_auto.
Functions for Managing Results from memcached
XXX http://hg.tangent.org/libmemcached/file/4001ba159d62/docs/memcached_result_st.pod
Functions for Deleting Values from memcached
See Memcached::libmemcached::memcached_delete.
memcached_delete
memcached_delete($memc, $key);
memcached_delete($memc, $key, $expiration);Delete $key. If $expiration is greater than zero then the key is deleted by memcached after that many seconds.
Functions for Accessing Statistics from memcached
See Memcached::libmemcached::memcached_stats.
Miscellaneous Functions
memcached_lib_version
$version = memcached_lib_version()Returns a simple version string, like "0.15", representing the libmemcached version (version of the client library, not server).
memcached_verbosity
memcached_verbosity($memc, $verbosity)Modifies the "verbosity" of the memcached servers associated with $memc.
memcached_quit
memcached_quit($memc)Disconnects from all servers
memcached_strerror
$string = memcached_strerror($memc, $return_code)memcached_strerror() takes a memcached_return value and returns a string describing the error. The string should be treated as read-only (it may be so in future versions). See also Memcached::libmemcached::memcached_strerror.
This function is rarely needed in the Perl interface because the return code is a dualvar that already contains the error string.
memcached_set_callback_coderefs
memcached_set_callback_coderefs($memc, \&set_callback, \&get_callback);This interface is experimental and likely to change. Currently only the get calback works.
Specify functions which will be executed when values are set and/or get using $memc.
When the callbacks are executed $_ is the value and the arguments are the key and flags value. Both $_ and the flags may be modified.
Currently the functions must return an empty list.
Unsupported Functions
(stats)
Grouping Keys On Servers
Normally libmemcached hashes the $key value to select which memcached server to communicate with. If you have several keys relating to a single object then it's very likely that the corresponding values will be stored in different memcached servers.
It would be more efficient, in general, when setting and getting multiple related values, if it was possible to specify a different value to be hashed to select which memcached server to communicate with. With libmemcached, you can.
Most of the functions for setting and getting values have *_by_key variants for exactly this reason. These all have an extra $master_key parameter immediately after the $memc parameter. For example:
memcached_mget($memc, \%keys, \%dest);
memcached_mget_by_key($memc, $maskey_key, \%keys, \%dest);The *_by_key variants all work in exactly the same way as the corresponding plain function, except that libmemcached hashes $master_key instead of $key to which memcached server to communicate with.
If $master_key is undef then the functions behave the same as their non-by-key variants, i.e., $key is used for hashing.
By-key variants of "Functions for Fetching Values":
memcached_get_by_key
memcached_mget_by_key
By-key variants of "Functions for Setting Values":
memcached_set_by_key
memcached_replace_by_key
memcached_add_by_key
memcached_append_by_key
memcached_cas_by_key
memcached_prepend_by_key
memcached_delete_by_key
EXTRA INFORMATION
Tracing Execution
The PERL_LIBMEMCACHED_TRACE environment variable can be used to control tracing. The value is read when memcached_create is called.
If set >= 1 then any non-success memcached_return value will be logged via warn().
If set >= 2 or more then some data types will list conversions of input and output values for function calls.
More flexible mechanisms will be added later.
Type Mapping
For pointer arguments, undef is mapped to null on input and null is mapped to undef on output.
XXX expand with details from typemap file
AUTHOR
Tim Bunce, <Tim.Bunce@pobox.com> with help from Patrick Galbraith and Daisuke Maki.
ACKNOWLEDGEMENTS
Larry Wall for Perl, Brad Fitzpatrick for memcached, Brian Aker for libmemcached, and Patrick Galbraith and Daisuke Maki for helping with the implementation.
PORTABILITY
See Slaven Rezic's excellent CPAN Testers Matrix at http://bbbike.radzeit.de/~slaven/cpantestersmatrix.cgi?dist=Memcached-libmemcached
Along with Dave Cantrell's excellent CPAN Dependency tracker at http://cpandeps.cantrell.org.uk/?module=Memcached%3A%3Alibmemcached&perl=any+version&os=any+OS
BUGS
Please report any bugs or feature requests to bug-memcached-libmemcached@rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Memcached-libmemcached. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
CONTRIBUTING
The source is hosted at http://perl-libmemcached.googlecode.com/ Patches and volunteers always welcome.
COPYRIGHT & LICENSE
Copyright 2008 Tim Bunce, All Rights Reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.