=begin rdoc
The Memcached client class.
=end
class Memcached
FLAGS = 0x0
DEFAULTS = {
:hash => :fnv1_32,
:no_block => false,
:distribution => :consistent_ketama,
:ketama_weighted => true,
:buffer_requests => false,
:cache_lookups => true,
:support_cas => false,
:tcp_nodelay => false,
:show_backtraces => false,
:retry_timeout => 30,
:timeout => 0.25,
:rcv_timeout => nil,
:poll_timeout => nil,
:connect_timeout => 2,
:prefix_key => nil,
:hash_with_prefix_key => true,
:default_ttl => 604800,
:default_weight => 8,
:sort_hosts => false,
:auto_eject_hosts => true,
:server_failure_limit => 2,
:verify_key => true,
:use_udp => false,
:binary_protocol => false
}
#:stopdoc:
IGNORED = 0
#:startdoc:
attr_reader :options # Return the options Hash used to configure this instance.
###### Configuration
=begin rdoc
Create a new Memcached instance. Accepts string or array of server strings, as well an an optional configuration hash.
Memcached.new('localhost', ...) # A single server
Memcached.new(['web001:11212', 'web002:11212'], ...) # Two servers with custom ports
Memcached.new(['web001:11211:2', 'web002:11211:8'], ...) # Two servers with default ports and explicit weights
Weights only affect Ketama hashing. If you use Ketama hashing and don't specify a weight, the client will poll each server's stats and use its size as the weight.
Valid option parameters are:
:prefix_key:: A string to prepend to every key, for namespacing. Max length is 127.
:hash:: The name of a hash function to use. Possible values are: :crc, :default, :fnv1_32, :fnv1_64, :fnv1a_32, :fnv1a_64, :hsieh, :md5, and :murmur. :fnv1_32 is fast and well known, and is the default. Use :md5 for compatibility with other ketama clients.
:distribution:: Either :modula, :consistent_ketama, :consistent_wheel, or :ketama. Defaults to :ketama.
:server_failure_limit:: How many consecutive failures to allow before marking a host as dead. Has no effect unless :retry_timeout is also set.
:retry_timeout:: How long to wait until retrying a dead server. Has no effect unless :server_failure_limit is non-zero. Defaults to 30.
:auto_eject_hosts:: Whether to temporarily eject dead hosts from the pool. Defaults to true. Note that in the event of an ejection, :auto_eject_hosts will remap the entire pool unless :distribution is set to :consistent.
:cache_lookups:: Whether to cache hostname lookups for the life of the instance. Defaults to true.
:support_cas:: Flag CAS support in the client. Accepts true or false. Defaults to false because it imposes a slight performance penalty. Note that your server must also support CAS or you will trigger Memcached::ProtocolError exceptions.
:tcp_nodelay:: Turns on the no-delay feature for connecting sockets. Accepts true or false. Performance may or may not change, depending on your system.
:no_block:: Whether to use pipelining for writes. Accepts true or false.
:buffer_requests:: Whether to use an internal write buffer. Accepts true or false. Calling get or closing the connection will force the buffer to flush. Note that :buffer_requests might not work well without :no_block also enabled.
:show_backtraces:: Whether Memcached::NotFound and Memcached::NotStored exceptions should include backtraces. Generating backtraces is slow, so this is off by default. Turn it on to ease debugging.
:connect_timeout:: How long to wait for a connection to a server. Defaults to 2 seconds. Set to 0 if you want to wait forever.
:timeout:: How long to wait for a response from the server. Defaults to 0.25 seconds. Set to 0 if you want to wait forever.
:default_ttl:: The ttl to use on set if no ttl is specified, in seconds. Defaults to one week. Set to 0 if you want things to never expire.
:default_weight:: The weight to use if :ketama_weighted is true, but no weight is specified for a server.
:hash_with_prefix_key:: Whether to include the prefix when calculating which server a key falls on. Defaults to true.
:use_udp:: Use the UDP protocol to reduce connection overhead. Defaults to false.
:binary_protocol:: Use the binary protocol to reduce query processing overhead. Defaults to false.
:sort_hosts:: Whether to force the server list to stay sorted. This defeats consistent hashing and is rarely useful.
:verify_key:: Validate keys before accepting them. Never disable this.
Please note that when pipelining is enabled, setter and deleter methods do not raise on errors. For example, if you try to set an invalid key with :no_block => true, it will appear to succeed. The actual setting of the key occurs after libmemcached has returned control to your program, so there is no way to backtrack and raise the exception.
=end
def initialize(servers = "localhost:11211", opts = {})
@struct = Lib::MemcachedSt.new
Lib.memcached_create(@struct)
# Merge option defaults and discard meaningless keys
@options = DEFAULTS.merge(opts)
@options.delete_if { |k,v| not DEFAULTS.keys.include? k }
@default_ttl = options[:default_ttl]
# Force :buffer_requests to use :no_block
# XXX Deleting the :no_block key should also work, but libmemcached doesn't seem to set it
# consistently
options[:no_block] = true if options[:buffer_requests]
# Disallow weights without ketama
options.delete(:ketama_weighted) if options[:distribution] != :consistent_ketama
# Legacy accessor
options[:prefix_key] = options.delete(:namespace) if options[:namespace]
# Disallow :sort_hosts with consistent hashing
if options[:sort_hosts] and options[:distribution] == :consistent
raise ArgumentError, ":sort_hosts defeats :consistent hashing"
end
# Read timeouts
options[:rcv_timeout] ||= options[:timeout] || 0
options[:poll_timeout] ||= options[:timeout] || 0
# Set the behaviors on the struct
set_behaviors
set_callbacks
# Freeze the hash
options.freeze
# Set the servers on the struct
set_servers(servers)
# Not found exceptions
unless options[:show_backtraces]
@not_found = NotFound.new
@not_found.no_backtrace = true
@not_stored = NotStored.new
@not_stored.no_backtrace = true
end
end
# Set the server list.
# FIXME Does not necessarily free any existing server structs.
def set_servers(servers)
Array(servers).each_with_index do |server, index|
# Socket
if server.is_a?(String) and File.socket?(server)
args = [@struct, server, options[:default_weight].to_i]
check_return_code(Lib.memcached_server_add_unix_socket_with_weight(*args))
# Network
elsif server.is_a?(String) and server =~ /^[\w\d\.-]+(:\d{1,5}){0,2}$/
host, port, weight = server.split(":")
args = [@struct, host, port.to_i, (weight || options[:default_weight]).to_i]
if options[:use_udp] #
check_return_code(Lib.memcached_server_add_udp_with_weight(*args))
else
check_return_code(Lib.memcached_server_add_with_weight(*args))
end
else
raise ArgumentError, "Servers must be either in the format 'host:port[:weight]' (e.g., 'localhost:11211' or 'localhost:11211:10') for a network server, or a valid path to a Unix domain socket (e.g., /var/run/memcached)."
end
end
# For inspect
@servers = send(:servers)
end
# Return the array of server strings used to configure this instance.
def servers
server_structs.map do |server|
inspect_server(server)
end
end
# Safely copy this instance. Returns a Memcached instance.
#
# clone is useful for threading, since each thread must have its own unshared Memcached
# object.
#
def clone
# FIXME Memory leak
# memcached = super
# struct = Lib.memcached_clone(nil, @struct)
# memcached.instance_variable_set('@struct', struct)
# memcached
self.class.new(servers, options)
end
# Reset the state of the libmemcached struct. This is useful for changing the server list at runtime.
def reset(current_servers = nil)
current_servers ||= servers
@struct = Lib::MemcachedSt.new
Lib.memcached_create(@struct)
set_behaviors
set_callbacks
set_servers(current_servers)
end
# Disconnect from all currently connected servers
def quit
Lib.memcached_quit(@struct)
self
end
#:stopdoc:
alias :dup :clone #:nodoc:
#:startdoc:
### Configuration helpers
private
# Return an array of raw memcached_host_st structs for this instance.
def server_structs
array = []
if @struct.hosts
@struct.hosts.count.times do |i|
array << Lib.memcached_select_server_at(@struct, i)
end
end
array
end
###### Operations
public
### Setters
# Set a key/value pair. Accepts a String key and an arbitrary Ruby object. Overwrites any existing value on the server.
#
# Accepts an optional ttl value to specify the maximum lifetime of the key on the server. ttl can be either an integer number of seconds, or a Time elapsed time object. 0 means no ttl. Note that there is no guarantee that the key will persist as long as the ttl, but it will not persist longer.
#
# Also accepts a marshal value, which defaults to true. Set marshal to false if you want the value to be set directly.
#
def set(key, value, ttl=@default_ttl, marshal=true, flags=FLAGS)
value = marshal ? Marshal.dump(value) : value.to_s
check_return_code(
Lib.memcached_set(@struct, key, value, ttl, flags),
key
)
rescue ClientError
# FIXME Memcached 1.2.8 occasionally rejects valid sets
tried = 1 and retry unless defined?(tried)
raise
end
# Add a key/value pair. Raises Memcached::NotStored if the key already exists on the server. The parameters are the same as set.
def add(key, value, ttl=@default_ttl, marshal=true, flags=FLAGS)
value = marshal ? Marshal.dump(value) : value.to_s
check_return_code(
Lib.memcached_add(@struct, key, value, ttl, flags),
key
)
end
# Increment a key's value. Accepts a String key. Raises Memcached::NotFound if the key does not exist.
#
# Also accepts an optional offset paramater, which defaults to 1. offset must be an integer.
#
# Note that the key must be initialized to an unmarshalled integer first, via set, add, or replace with marshal set to false.
def increment(key, offset=1)
ret, value = Lib.memcached_increment(@struct, key, offset)
check_return_code(ret, key)
value
end
# Decrement a key's value. The parameters and exception behavior are the same as increment.
def decrement(key, offset=1)
ret, value = Lib.memcached_decrement(@struct, key, offset)
check_return_code(ret, key)
value
end
#:stopdoc:
alias :incr :increment
alias :decr :decrement
#:startdoc:
# Replace a key/value pair. Raises Memcached::NotFound if the key does not exist on the server. The parameters are the same as set.
def replace(key, value, ttl=@default_ttl, marshal=true, flags=FLAGS)
value = marshal ? Marshal.dump(value) : value.to_s
check_return_code(
Lib.memcached_replace(@struct, key, value, ttl, flags),
key
)
end
# Appends a string to a key's value. Accepts a String key and a String value. Raises Memcached::NotFound if the key does not exist on the server.
#
# Note that the key must be initialized to an unmarshalled string first, via set, add, or replace with marshal set to false.
def append(key, value)
# Requires memcached 1.2.4
check_return_code(
Lib.memcached_append(@struct, key, value.to_s, IGNORED, IGNORED),
key
)
end
# Prepends a string to a key's value. The parameters and exception behavior are the same as append.
def prepend(key, value)
# Requires memcached 1.2.4
check_return_code(
Lib.memcached_prepend(@struct, key, value.to_s, IGNORED, IGNORED),
key
)
end
# Reads a key's value from the server and yields it to a block. Replaces the key's value with the result of the block as long as the key hasn't been updated in the meantime, otherwise raises Memcached::NotStored. Accepts a String key and a block.
#
# Also accepts an optional ttl value.
#
# CAS stands for "compare and swap", and avoids the need for manual key mutexing. CAS support must be enabled in Memcached.new or a Memcached::ClientError will be raised. Note that CAS may be buggy in memcached itself.
#
def cas(key, ttl=@default_ttl, marshal=true, flags=FLAGS)
raise ClientError, "CAS not enabled for this Memcached instance" unless options[:support_cas]
value, flags, ret = Lib.memcached_get_rvalue(@struct, key)
check_return_code(ret, key)
cas = @struct.result.cas
value = Marshal.load(value) if marshal
value = yield value
value = Marshal.dump(value) if marshal
check_return_code(Lib.memcached_cas(@struct, key, value, ttl, flags, cas), key)
end
alias :compare_and_swap :cas
### Deleters
# Deletes a key/value pair from the server. Accepts a String key. Raises Memcached::NotFound if the key does not exist.
def delete(key)
check_return_code(
Lib.memcached_delete(@struct, key, IGNORED),
key
)
end
# Flushes all key/value pairs from all the servers.
def flush
check_return_code(
Lib.memcached_flush(@struct, IGNORED)
)
end
### Getters
# Gets a key's value from the server. Accepts a String key or array of String keys.
#
# Also accepts a marshal value, which defaults to true. Set marshal to false if you want the value to be returned directly as a String. Otherwise it will be assumed to be a marshalled Ruby object and unmarshalled.
#
# If you pass a String key, and the key does not exist on the server, Memcached::NotFound will be raised. If you pass an array of keys, memcached's multiget mode will be used, and a hash of key/value pairs will be returned. The hash will contain only the keys that were found.
#
# The multiget behavior is subject to change in the future; however, for multiple lookups, it is much faster than normal mode.
#
# Note that when you rescue Memcached::NotFound exceptions, you should use a the block rescue syntax instead of the inline syntax. Block rescues are very fast, but inline rescues are very slow.
#
def get(keys, marshal=true)
if keys.is_a? Array
# Multi get
ret = Lib.memcached_mget(@struct, keys);
check_return_code(ret, keys)
hash = {}
keys.each do
value, key, flags, ret = Lib.memcached_fetch_rvalue(@struct)
break if ret == Lib::MEMCACHED_END
check_return_code(ret, key)
# Assign the value
hash[key] = (marshal ? Marshal.load(value) : value)
end
hash
else
# Single get
value, flags, ret = Lib.memcached_get_rvalue(@struct, keys)
check_return_code(ret, keys)
marshal ? Marshal.load(value) : value
end
end
### Information methods
# Return the server used by a particular key.
def server_by_key(key)
ret = Lib.memcached_server_by_key(@struct, key)
if ret.is_a?(Array)
string = inspect_server(ret.first)
Rlibmemcached.memcached_server_free(ret.first)
string
end
end
# Return a Hash of statistics responses from the set of servers. Each value is an array with one entry for each server, in the same order the servers were defined.
def stats
stats = Hash.new([])
stat_struct, ret = Lib.memcached_stat(@struct, "")
check_return_code(ret)
keys, ret = Lib.memcached_stat_get_keys(@struct, stat_struct)
check_return_code(ret)
keys.each do |key|
server_structs.size.times do |index|
value, ret = Lib.memcached_stat_get_rvalue(
@struct,
Lib.memcached_select_stat_at(@struct, stat_struct, index),
key)
check_return_code(ret, key)
value = case value
when /^\d+\.\d+$/ then value.to_f
when /^\d+$/ then value.to_i
else value
end
stats[key.to_sym] += [value]
end
end
Lib.memcached_stat_free(@struct, stat_struct)
stats
rescue Memcached::SomeErrorsWereReported => _
e = _.class.new("Error getting stats")
e.set_backtrace(_.backtrace)
raise e
end
### Operations helpers
private
# Checks the return code from Rlibmemcached against the exception list. Raises the corresponding exception if the return code is not Memcached::Success or Memcached::ActionQueued. Accepts an integer return code and an optional key, for exception messages.
def check_return_code(ret, key = nil) #:doc:
if ret == 0 # Memcached::Success
elsif ret == Lib::MEMCACHED_BUFFERED # Memcached::ActionQueued
elsif ret == Lib::MEMCACHED_NOTFOUND and @not_found
raise @not_found
elsif ret == Lib::MEMCACHED_NOTSTORED and @not_stored
raise @not_stored
else
message = "Key #{inspect_keys(key, (detect_failure if ret == Lib::MEMCACHED_SERVER_MARKED_DEAD)).inspect}"
if key.is_a?(String)
if ret == Lib::MEMCACHED_ERRNO
server = Lib.memcached_server_by_key(@struct, key)
errno = server.first.cached_errno
message = "Errno #{errno}: #{ERRNO_HASH[errno].inspect}. #{message}"
elsif ret == Lib::MEMCACHED_SERVER_ERROR
server = Lib.memcached_server_by_key(@struct, key)
message = "\"#{server.first.cached_server_error}\". #{message}."
end
end
raise EXCEPTIONS[ret], message
end
end
# Turn an array of keys into a hash of keys to servers.
def inspect_keys(keys, server = nil)
Hash[*Array(keys).map do |key|
[key, server || server_by_key(key)]
end.flatten]
end
# Find which server failed most recently.
# FIXME Is this still necessary with cached_errno?
def detect_failure
time = Time.now
server = server_structs.detect do |server|
server.next_retry > time
end
inspect_server(server) if server
end
# Set the behaviors on the struct from the current options.
def set_behaviors
BEHAVIORS.keys.each do |behavior|
set_behavior(behavior, options[behavior]) if options.key?(behavior)
end
# BUG Hash must be last due to the weird Libmemcached multi-behaviors
set_behavior(:hash, options[:hash])
end
# Set the callbacks on the struct from the current options.
def set_callbacks
# Only support prefix_key for now
if options[:prefix_key]
unless options[:prefix_key].size < Lib::MEMCACHED_PREFIX_KEY_MAX_SIZE
raise ArgumentError, "Max prefix_key size is #{Lib::MEMCACHED_PREFIX_KEY_MAX_SIZE - 1}"
end
Lib.memcached_callback_set(@struct, Lib::MEMCACHED_CALLBACK_PREFIX_KEY, options[:prefix_key])
end
end
def is_unix_socket?(server)
server.type == Lib::MEMCACHED_CONNECTION_UNIX_SOCKET
end
# Stringify an opaque server struct
def inspect_server(server)
strings = [server.hostname]
if !is_unix_socket?(server)
strings << ":#{server.port}"
strings << ":#{server.weight}" if options[:ketama_weighted]
end
strings.join
end
end