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

new(servers = nil, options = {}) click to toggle source

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 49
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

add(key, value, ttl = nil, req_options = nil) click to toggle source

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 214
def add(key, value, ttl = nil, req_options = nil)
  perform(:add, key, value, ttl_or_default(ttl), req_options)
end
alive!() click to toggle source

Make sure memcache servers are alive, or raise an Dalli::RingError

# File lib/dalli/client.rb, line 342
def alive!
  ring.server_for_key('')
end
append(key, value) click to toggle source

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 246
def append(key, value)
  perform(:append, key, value.to_s)
end
cache_nils() click to toggle source
# File lib/dalli/client.rb, line 361
def cache_nils
  @options[:cache_nils]
end
cas(key, ttl = nil, req_options = nil, &block) click to toggle source

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 158
def cas(key, ttl = nil, req_options = nil, &block)
  cas_core(key, false, ttl, req_options, &block)
end
cas!(key, ttl = nil, req_options = nil, &block) click to toggle source

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 169
def cas!(key, ttl = nil, req_options = nil, &block)
  cas_core(key, true, ttl, req_options, &block)
end
close() click to toggle source

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 349
def close
  @ring&.close
  @ring = nil
end
Also aliased as: reset
decr(key, amt = 1, ttl = nil, default = nil) click to toggle source

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 292
def decr(key, amt = 1, ttl = nil, default = nil)
  check_positive!(amt)

  perform(:decr, key, amt.to_i, ttl_or_default(ttl), default)
end
delete(key) click to toggle source
# File lib/dalli/client.rb, line 239
def delete(key)
  delete_cas(key, 0)
end
delete_cas(key, cas = 0) click to toggle source

Delete a key/value pair, verifying existing CAS. Returns true if succeeded, and falsy otherwise.

# File lib/dalli/client.rb, line 235
def delete_cas(key, cas = 0)
  perform(:delete, key, cas)
end
fetch(key, ttl = nil, req_options = nil) { || ... } click to toggle source

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 137
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(delay = 0) click to toggle source

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 302
def flush(delay = 0)
  ring.servers.map { |s| s.request(:flush, delay) }
end
Also aliased as: flush_all
flush_all(delay = 0)
Alias for: flush
gat(key, ttl = nil) click to toggle source

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 71
def gat(key, ttl = nil)
  perform(:gat, key, ttl_or_default(ttl))
end
get(key, req_options = nil) click to toggle source

Get the value associated with the key. If a value is not found, then nil is returned.

# File lib/dalli/client.rb, line 63
def get(key, req_options = nil)
  perform(:get, key, req_options)
end
get_cas(key) { |value, cas| ... } click to toggle source

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 87
def get_cas(key)
  (value, cas) = perform(:cas, key)
  return [value, cas] unless block_given?

  yield value, cas
end
get_multi(*keys) { |k, first| ... } click to toggle source

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 98
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
get_multi_cas(*keys) { |*args| ... } click to toggle source

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 119
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(key, amt = 1, ttl = nil, default = nil) click to toggle source

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 270
def incr(key, amt = 1, ttl = nil, default = nil)
  check_positive!(amt)

  perform(:incr, key, amt.to_i, ttl_or_default(ttl), default)
end
multi()
Alias for: quiet
not_found?(val) click to toggle source
# File lib/dalli/client.rb, line 357
def not_found?(val)
  cache_nils ? val == ::Dalli::NOT_FOUND : val.nil?
end
prepend(key, value) click to toggle source

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 253
def prepend(key, value)
  perform(:prepend, key, value.to_s)
end
quiet() { || ... } click to toggle source

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 190
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
Also aliased as: multi
replace(key, value, ttl = nil, req_options = nil) click to toggle source

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 221
def replace(key, value, ttl = nil, req_options = nil)
  replace_cas(key, value, 0, ttl, req_options)
end
replace_cas(key, value, cas, ttl = nil, req_options = nil) click to toggle source

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 229
def replace_cas(key, value, cas, ttl = nil, req_options = nil)
  perform(:replace, key, value, ttl_or_default(ttl), cas, req_options)
end
reset()
Alias for: close
reset_stats() click to toggle source

Reset stats for each server.

# File lib/dalli/client.rb, line 324
def reset_stats
  ring.servers.map do |server|
    server.alive? ? server.request(:reset_stats) : nil
  end
end
set(key, value, ttl = nil, req_options = nil) click to toggle source
# File lib/dalli/client.rb, line 200
def set(key, value, ttl = nil, req_options = nil)
  set_cas(key, value, 0, ttl, req_options)
end
set_cas(key, value, cas, ttl = nil, req_options = nil) click to toggle source

Set the key-value pair, verifying existing CAS. Returns the resulting CAS value if succeeded, and falsy otherwise.

# File lib/dalli/client.rb, line 207
def set_cas(key, value, cas, ttl = nil, req_options = nil)
  perform(:set, key, value, ttl_or_default(ttl), cas, req_options)
end
stats(type = nil) click to toggle source

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 313
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(key, ttl = nil) click to toggle source

Touch updates expiration time for a given key.

Returns true if key exists, otherwise nil.

# File lib/dalli/client.rb, line 79
def touch(key, ttl = nil)
  resp = perform(:touch, key, ttl_or_default(ttl))
  resp.nil? ? nil : true
end
version() click to toggle source

Version of the memcache servers.

# File lib/dalli/client.rb, line 332
def version
  values = {}
  ring.servers.each do |server|
    values[server.name.to_s] = server.alive? ? server.request(:version) : nil
  end
  values
end
with() { |self| ... } click to toggle source

Stub method so a bare Dalli client can pretend to be a connection pool.

# File lib/dalli/client.rb, line 366
def with
  yield self
end

Private Instance Methods

cas_core(key, always_set, ttl = nil, req_options = nil) { |value| ... } click to toggle source
# File lib/dalli/client.rb, line 376
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
check_positive!(amt) click to toggle source
# File lib/dalli/client.rb, line 372
def check_positive!(amt)
  raise ArgumentError, "Positive values only: #{amt}" if amt.negative?
end
normalize_options(opts) click to toggle source
# File lib/dalli/client.rb, line 439
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
perform(*all_args) { || ... } click to toggle source

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 423
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
pipelined_getter() click to toggle source
# File lib/dalli/client.rb, line 446
def pipelined_getter
  PipelinedGetter.new(ring, @key_manager)
end
protocol_implementation() click to toggle source
# File lib/dalli/client.rb, line 404
def protocol_implementation
  @protocol_implementation ||= case @options[:protocol]&.to_s
                               when 'meta'
                                 Dalli::Protocol::Meta
                               else
                                 Dalli::Protocol::Binary
                               end
end
ring() click to toggle source
# File lib/dalli/client.rb, line 394
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
ttl_or_default(ttl) click to toggle source

Uses the argument TTL or the client-wide default. Ensures that the value is an integer

# File lib/dalli/client.rb, line 388
def ttl_or_default(ttl)
  (ttl || @options[:expires_in]).to_i
rescue NoMethodError
  raise ArgumentError, "Cannot convert ttl (#{ttl}) to an integer"
end