class Dalli::Client
Dalli::Client is the main class which developers will use to interact with Memcached.
Constants
- ALLOWED_STAT_KEYS
- CACHE_NILS
Public Class Methods
Dalli::Client is the main class which developers will use to interact with the memcached server. Usage:
Dalli::Client.new(['localhost:11211:10', 'cache-2.example.com:11211:5', '192.168.0.1:22122:5', '/var/run/memcached/socket'], failover: true, expires_in: 300)
servers is an Array of “host:port:weight” where weight allows you to
distribute cache unevenly. Both weight and port are optional. If you pass
in nil, Dalli will use the
MEMCACHE_SERVERS
environment variable or default to
'localhost:11211' if it is not present. Dalli also supports the ability to connect to
Memcached on localhost through a UNIX socket. To use this functionality,
use a full pathname (beginning with a slash character '/') in place
of the “host:port” pair in the server configuration.
Options:
-
:namespace - prepend each key with this value to provide simple namespacing.
-
:failover - if a server is down, look for and store values on another server in the ring. Default: true.
-
:threadsafe - ensure that only one thread is actively using a socket at a time. Default: true.
-
:expires_in - default TTL in seconds if you do not pass TTL as a parameter to an individual operation, defaults
to 0 or forever.
-
:compress - if true Dalli will compress values larger than compression_min_size bytes before sending them
to memcached. Default: true.
-
:compression_min_size - the minimum size (in bytes) for which Dalli will compress values sent to Memcached.
Defaults to 4K.
-
:serializer - defaults to Marshal
-
:compressor - defaults to Dalli::Compressor, a Zlib-based implementation
-
:cache_nils - defaults to false, if true Dalli will not treat cached nil values as 'not found' for
#fetch operations.
-
:digest_class - defaults to Digest::MD5, allows you to pass in an object that responds to the hexdigest method,
useful for injecting a FIPS compliant hash object.
-
:protocol - one of either :binary or :meta, defaulting to :binary. This sets the protocol that Dalli uses
to communicate with memcached.
# File lib/dalli/client.rb, line 48 def initialize(servers = nil, options = {}) @servers = ::Dalli::ServersArgNormalizer.normalize_servers(servers) @options = normalize_options(options) @key_manager = ::Dalli::KeyManager.new(@options) @ring = nil end
Public Instance Methods
Conditionally add a key/value pair, if the key does not already exist on the server. Returns truthy if the operation succeeded.
# File lib/dalli/client.rb, line 213 def add(key, value, ttl = nil, req_options = nil) perform(:add, key, value, ttl_or_default(ttl), req_options) end
Make sure memcache servers are alive, or raise an Dalli::RingError
# File lib/dalli/client.rb, line 341 def alive! ring.server_for_key('') end
Append value to the value already stored on the server for 'key'. Appending only works for values stored with :raw => true.
# File lib/dalli/client.rb, line 245 def append(key, value) perform(:append, key, value.to_s) end
# File lib/dalli/client.rb, line 360 def cache_nils @options[:cache_nils] end
compare and swap values using optimistic locking. Fetch the existing value for key. If it exists, yield the value to the block. Add the block's return value as the new value for the key. Add will fail if someone else changed the value.
Returns:
-
nil if the key did not exist.
-
false if the value was changed by someone else.
-
true if the value was successfully updated.
# File lib/dalli/client.rb, line 157 def cas(key, ttl = nil, req_options = nil, &block) cas_core(key, false, ttl, req_options, &block) end
like cas, but will yield to the block whether or not the value already exists.
Returns:
-
false if the value was changed by someone else.
-
true if the value was successfully updated.
# File lib/dalli/client.rb, line 168 def cas!(key, ttl = nil, req_options = nil, &block) cas_core(key, true, ttl, req_options, &block) end
Close our connection to each server. If you perform another operation after this, the connections will be re-established.
# File lib/dalli/client.rb, line 348 def close @ring&.close @ring = nil end
Decr subtracts the given amount from the counter on the memcached server. Amt must be a positive integer value.
memcached counters are unsigned and cannot hold negative values. Calling decr on a counter which is 0 will just return 0.
If default is nil, the counter must already exist or the operation will fail and will return nil. Otherwise this method will return the new value for the counter.
Note that the ttl will only apply if the counter does not already exist. To decrease an existing counter and update its TTL, use cas.
If the value already exists, it must have been set with raw: true
# File lib/dalli/client.rb, line 291 def decr(key, amt = 1, ttl = nil, default = nil) check_positive!(amt) perform(:decr, key, amt.to_i, ttl_or_default(ttl), default) end
# File lib/dalli/client.rb, line 238 def delete(key) delete_cas(key, 0) end
Delete a key/value pair, verifying existing CAS. Returns true if succeeded, and falsy otherwise.
# File lib/dalli/client.rb, line 234 def delete_cas(key, cas = 0) perform(:delete, key, cas) end
Fetch the value associated with the key. If a value is found, then it is returned.
If a value is not found and no block is given, then nil is returned.
If a value is not found (or if the found value is nil and :cache_nils is false) and a block is given, the block will be invoked and its return value written to the cache and returned.
# File lib/dalli/client.rb, line 136 def fetch(key, ttl = nil, req_options = nil) req_options = req_options.nil? ? CACHE_NILS : req_options.merge(CACHE_NILS) if cache_nils val = get(key, req_options) return val unless block_given? && not_found?(val) new_val = yield add(key, new_val, ttl_or_default(ttl), req_options) new_val end
Flush the memcached server, at 'delay' seconds in the future. Delay defaults to zero seconds, which means an immediate flush.
# File lib/dalli/client.rb, line 301 def flush(delay = 0) ring.servers.map { |s| s.request(:flush, delay) } end
Gat (get and touch) fetch an item and simultaneously update its expiration time.
If a value is not found, then nil
is returned.
# File lib/dalli/client.rb, line 70 def gat(key, ttl = nil) perform(:gat, key, ttl_or_default(ttl)) end
Get the value associated with the key. If a value is not found, then
nil
is returned.
# File lib/dalli/client.rb, line 62 def get(key, req_options = nil) perform(:get, key, req_options) end
Get the value and CAS ID associated with the key. If a block is provided, value and CAS will be passed to the block.
# File lib/dalli/client.rb, line 86 def get_cas(key) (value, cas) = perform(:cas, key) return [value, cas] unless block_given? yield value, cas end
Fetch multiple keys efficiently. If a block is given, yields key/value pairs one at a time. Otherwise returns a hash of { 'key' => 'value', 'key2' => 'value1' }
# File lib/dalli/client.rb, line 97 def get_multi(*keys) keys.flatten! keys.compact! return {} if keys.empty? if block_given? pipelined_getter.process(keys) { |k, data| yield k, data.first } else {}.tap do |hash| pipelined_getter.process(keys) { |k, data| hash[k] = data.first } end end end
Fetch multiple keys efficiently, including available metadata such as CAS. If a block is given, yields key/data pairs one a time. Data is an array:
- value, cas_id
-
If no block is given, returns a hash of
{ 'key' => [value, cas_id] }
# File lib/dalli/client.rb, line 118 def get_multi_cas(*keys) if block_given? pipelined_getter.process(keys) { |*args| yield(*args) } else {}.tap do |hash| pipelined_getter.process(keys) { |k, data| hash[k] = data } end end end
Incr adds the given amount to the counter on the memcached server. Amt must be a positive integer value.
If default is nil, the counter must already exist or the operation will fail and will return nil. Otherwise this method will return the new value for the counter.
Note that the ttl will only apply if the counter does not already exist. To increase an existing counter and update its TTL, use cas.
If the value already exists, it must have been set with raw: true
# File lib/dalli/client.rb, line 269 def incr(key, amt = 1, ttl = nil, default = nil) check_positive!(amt) perform(:incr, key, amt.to_i, ttl_or_default(ttl), default) end
# File lib/dalli/client.rb, line 356 def not_found?(val) cache_nils ? val == ::Dalli::NOT_FOUND : val.nil? end
Prepend value to the value already stored on the server for 'key'. Prepending only works for values stored with :raw => true.
# File lib/dalli/client.rb, line 252 def prepend(key, value) perform(:prepend, key, value.to_s) end
Turn on quiet aka noreply support for a number of memcached operations.
All relevant operations within this block will be effectively pipelined as Dalli will use 'quiet' versions. The invoked methods will all return nil, rather than their usual response. Method latency will be substantially lower, as the caller will not be blocking on responses.
Currently supports storage (set, add, replace, append, prepend), arithmetic (incr, decr), flush and delete operations. Use of unsupported operations inside a block will raise an error.
Any error replies will be discarded at the end of the block, and Dalli client methods invoked inside the block will not have return values
# File lib/dalli/client.rb, line 189 def quiet old = Thread.current[::Dalli::QUIET] Thread.current[::Dalli::QUIET] = true yield ensure @ring&.pipeline_consume_and_ignore_responses Thread.current[::Dalli::QUIET] = old end
Conditionally add a key/value pair, only if the key already exists on the server. Returns truthy if the operation succeeded.
# File lib/dalli/client.rb, line 220 def replace(key, value, ttl = nil, req_options = nil) replace_cas(key, value, 0, ttl, req_options) end
Conditionally add a key/value pair, verifying existing CAS, only if the key already exists on the server. Returns the new CAS value if the operation succeeded, or falsy otherwise.
# File lib/dalli/client.rb, line 228 def replace_cas(key, value, cas, ttl = nil, req_options = nil) perform(:replace, key, value, ttl_or_default(ttl), cas, req_options) end
Reset stats for each server.
# File lib/dalli/client.rb, line 323 def reset_stats ring.servers.map do |server| server.alive? ? server.request(:reset_stats) : nil end end
# File lib/dalli/client.rb, line 199 def set(key, value, ttl = nil, req_options = nil) set_cas(key, value, 0, ttl, req_options) end
Set the key-value pair, verifying existing CAS. Returns the resulting CAS value if succeeded, and falsy otherwise.
# File lib/dalli/client.rb, line 206 def set_cas(key, value, cas, ttl = nil, req_options = nil) perform(:set, key, value, ttl_or_default(ttl), cas, req_options) end
Collect the stats for each server. You can optionally pass a type including :items, :slabs or :settings to get specific stats Returns a hash like { 'hostname:port' => { 'stat1' => 'value1', … }, 'hostname2:port' => { … } }
# File lib/dalli/client.rb, line 312 def stats(type = nil) type = nil unless ALLOWED_STAT_KEYS.include? type values = {} ring.servers.each do |server| values[server.name.to_s] = server.alive? ? server.request(:stats, type.to_s) : nil end values end
Touch updates expiration time for a given key.
Returns true if key exists, otherwise nil.
# File lib/dalli/client.rb, line 78 def touch(key, ttl = nil) resp = perform(:touch, key, ttl_or_default(ttl)) resp.nil? ? nil : true end
Version of the memcache servers.
# File lib/dalli/client.rb, line 331 def version values = {} ring.servers.each do |server| values[server.name.to_s] = server.alive? ? server.request(:version) : nil end values end
Stub method so a bare Dalli client can pretend to be a connection pool.
# File lib/dalli/client.rb, line 365 def with yield self end
Private Instance Methods
# File lib/dalli/client.rb, line 375 def cas_core(key, always_set, ttl = nil, req_options = nil) (value, cas) = perform(:cas, key) return if value.nil? && !always_set newvalue = yield(value) perform(:set, key, newvalue, ttl_or_default(ttl), cas, req_options) end
# File lib/dalli/client.rb, line 371 def check_positive!(amt) raise ArgumentError, "Positive values only: #{amt}" if amt.negative? end
# File lib/dalli/client.rb, line 438 def normalize_options(opts) opts[:expires_in] = opts[:expires_in].to_i if opts[:expires_in] opts rescue NoMethodError raise ArgumentError, "cannot convert :expires_in => #{opts[:expires_in].inspect} to an integer" end
Chokepoint method for memcached methods with a key argument. Validates the key, resolves the key to the appropriate server instance, and invokes the memcached method on the appropriate server.
This method also forces retries on network errors - when a particular memcached instance becomes unreachable, or the operational times out.
# File lib/dalli/client.rb, line 422 def perform(*all_args) return yield if block_given? op, key, *args = all_args key = key.to_s key = @key_manager.validate_key(key) server = ring.server_for_key(key) server.request(op, key, *args) rescue NetworkError => e Dalli.logger.debug { e.inspect } Dalli.logger.debug { 'retrying request with new server' } retry end
# File lib/dalli/client.rb, line 445 def pipelined_getter PipelinedGetter.new(ring, @key_manager) end
# File lib/dalli/client.rb, line 403 def protocol_implementation @protocol_implementation ||= case @options[:protocol]&.to_s when 'meta' Dalli::Protocol::Meta else Dalli::Protocol::Binary end end
# File lib/dalli/client.rb, line 393 def ring # TODO: This server initialization should probably be pushed down # to the Ring @ring ||= Dalli::Ring.new( @servers.map do |s| protocol_implementation.new(s, @options) end, @options ) end
Uses the argument TTL or the client-wide default. Ensures that the value is an integer
# File lib/dalli/client.rb, line 387 def ttl_or_default(ttl) (ttl || @options[:expires_in]).to_i rescue NoMethodError raise ArgumentError, "Cannot convert ttl (#{ttl}) to an integer" end