Class: MemCache

Inherits:
Object
  • Object
show all
Defined in:
lib/memcache.rb,
lib/memcache/version.rb,
lib/memcache/event_machine.rb

Overview

A Ruby client library for memcached.

Defined Under Namespace

Modules: EventedServer Classes: BufferedIO, MemCacheError, Server

Constant Summary collapse

DEFAULT_OPTIONS =

Default options for the cache object.

{
  :namespace    => nil,
  :readonly     => false,
  :multithread  => true,
  :failover     => true,
  :timeout      => 0.5,
  :logger       => nil,
  :no_reply     => false,
  :check_size   => true,
  :autofix_keys => false,
  :namespace_separator => ':',
}
DEFAULT_PORT =

Default memcached port.

11211
DEFAULT_WEIGHT =

Default memcached server weight.

1
ONE_MB =

Add key to the cache with value value that expires in expiry seconds. If raw is true, value will not be Marshalled.

Warning: Readers should not call this method in the event of a cache miss; see MemCache#add.

1024 * 1024
VERSION =

The version of MemCache you are using.

"1.8.5"

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ MemCache

Accepts a list of servers and a list of opts. servers may be omitted. See servers= for acceptable server list arguments.

Valid options for opts are:

[:namespace]    Prepends this value to all keys added or retrieved.
[:readonly]     Raises an exception on cache writes when true.
[:multithread]  Wraps cache access in a Mutex for thread safety. Defaults to true.
[:failover]     Should the client try to failover to another server if the
                first server is down?  Defaults to true.
[:timeout]      Time to use as the socket read timeout.  Defaults to 0.5 sec,
                set to nil to disable timeouts.
[:logger]       Logger to use for info/debug output, defaults to nil
[:no_reply]     Don't bother looking for a reply for write operations (i.e. they
                become 'fire and forget'), memcached 1.2.5 and later only, speeds up
                set/add/delete/incr/decr significantly.
[:check_size]   Raises a MemCacheError if the value to be set is greater than 1 MB, which
                is the maximum key size for the standard memcached server.  Defaults to true.
[:autofix_keys] If a key is longer than 250 characters or contains spaces,
                use an SHA1 hash instead, to prevent collisions on truncated keys.

Other options are ignored.



142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
# File 'lib/memcache.rb', line 142

def initialize(*args)
  servers = []
  opts = {}

  case args.length
  when 0 then # NOP
  when 1 then
    arg = args.shift
    case arg
    when Hash   then opts = arg
    when Array  then servers = arg
    when String then servers = [arg]
    else raise ArgumentError, 'first argument must be Array, Hash or String'
    end
  when 2 then
    servers, opts = args
  else
    raise ArgumentError, "wrong number of arguments (#{args.length} for 2)"
  end

  @evented = defined?(EM) && EM.reactor_running?
  opts = DEFAULT_OPTIONS.merge opts
  @namespace    = opts[:namespace]
  @readonly     = opts[:readonly]
  @multithread  = opts[:multithread] && !@evented
  @autofix_keys = opts[:autofix_keys]
  @timeout      = opts[:timeout]
  @failover     = opts[:failover]
  @logger       = opts[:logger]
  @no_reply     = opts[:no_reply]
  @check_size   = opts[:check_size]
  @namespace_separator = opts[:namespace_separator]
  @mutex        = Mutex.new if @multithread

  logger.info { "memcache-client #{VERSION} #{Array(servers).inspect}" } if logger

  Thread.current[:memcache_client] = self.object_id if !@multithread
  

  self.servers = servers
end

Instance Attribute Details

#autofix_keysObject (readonly)

Whether to try to fix keys that are too long and will be truncated by using their SHA1 hash instead. The hash is only used on keys longer than 250 characters, or containing spaces, to avoid impacting performance unnecesarily.

In theory, your code should generate correct keys when calling memcache, so it's your responsibility and you should try to fix this problem at its source.

But if that's not possible, enable this option and memcache-client will give you a hand.



89
90
91
# File 'lib/memcache.rb', line 89

def autofix_keys
  @autofix_keys
end

#failoverObject (readonly)

Should the client try to failover to another server if the first server is down? Defaults to true.



106
107
108
# File 'lib/memcache.rb', line 106

def failover
  @failover
end

#loggerObject (readonly)

Log debug/info/warn/error to the given Logger, defaults to nil.



111
112
113
# File 'lib/memcache.rb', line 111

def logger
  @logger
end

#multithreadObject (readonly)

The multithread setting for this instance



76
77
78
# File 'lib/memcache.rb', line 76

def multithread
  @multithread
end

#namespaceObject (readonly)

The namespace for this instance



71
72
73
# File 'lib/memcache.rb', line 71

def namespace
  @namespace
end

#no_replyObject (readonly)

Don't send or look for a reply from the memcached server for write operations. Please note this feature only works in memcached 1.2.5 and later. Earlier versions will reply with “ERROR”.



117
118
119
# File 'lib/memcache.rb', line 117

def no_reply
  @no_reply
end

#serversObject

The servers this client talks to. Play at your own peril.



94
95
96
# File 'lib/memcache.rb', line 94

def servers
  @servers
end

#timeoutObject (readonly)

Socket timeout limit with this client, defaults to 0.5 sec. Set to nil to disable timeouts.



100
101
102
# File 'lib/memcache.rb', line 100

def timeout
  @timeout
end

Instance Method Details

#[]=(key, value) ⇒ Object

Shortcut to save a value in the cache. This method does not set an expiration on the entry. Use set to specify an explicit expiry.



665
666
667
# File 'lib/memcache.rb', line 665

def []=(key, value)
  set key, value
end

#active?Boolean

Returns whether there is at least one active server for the object.

Returns:

  • (Boolean)


195
196
197
# File 'lib/memcache.rb', line 195

def active?
  not @servers.empty?
end

#add(key, value, expiry = 0, raw = false) ⇒ Object

Add key to the cache with value value that expires in expiry seconds, but only if key does not already exist in the cache. If raw is true, value will not be Marshalled.

Readers should call this method in the event of a cache miss, not MemCache#set.

Raises:



444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
# File 'lib/memcache.rb', line 444

def add(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  value = Marshal.dump value unless raw
  with_server(key) do |server, cache_key|
    logger.debug { "add #{key} to #{server}: #{value ? value.to_s.bytesize : 'nil'}" } if logger
    command = "add #{cache_key} 0 #{expiry} #{value.to_s.bytesize}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#append(key, value) ⇒ Object

Append - 'add this data to an existing key after existing data' Please note the value is always passed to memcached as raw since it doesn't make a lot of sense to concatenate marshalled data together.

Raises:



486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
# File 'lib/memcache.rb', line 486

def append(key, value)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    logger.debug { "append #{key} to #{server}: #{value ? value.to_s.bytesize : 'nil'}" } if logger
    command = "append #{cache_key} 0 0 #{value.to_s.bytesize}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#cache_decr(server, cache_key, amount) ⇒ Object

Performs a raw decr for cache_key from server. Returns nil if not found.



730
731
732
733
734
735
736
737
738
739
# File 'lib/memcache.rb', line 730

def cache_decr(server, cache_key, amount)
  with_socket_management(server) do |socket|
    socket.write "decr #{cache_key} #{amount}#{noreply}\r\n"
    break nil if @no_reply
    text = socket.gets
    raise_on_error_response! text
    return nil if text == "NOT_FOUND\r\n"
    return text.to_i
  end
end

#cache_get(server, cache_key) ⇒ Object

Fetches the raw data for cache_key from server. Returns nil on cache miss.



745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
# File 'lib/memcache.rb', line 745

def cache_get(server, cache_key)
  with_socket_management(server) do |socket|
    socket.write "get #{cache_key}\r\n"
    keyline = socket.gets # "VALUE <key> <flags> <bytes>\r\n"

    if keyline.nil? then
      server.close
      raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
    end

    raise_on_error_response! keyline
    return nil if keyline == "END\r\n"

    unless keyline =~ /(\d+)\r/ then
      server.close
      raise MemCacheError, "unexpected response #{keyline.inspect}"
    end
    value = socket.read $1.to_i
    socket.read 2 # "\r\n"
    socket.gets   # "END\r\n"
    return value
  end
end

#cache_get_multi(server, cache_keys) ⇒ Object

Fetches cache_keys from server using a multi-get.



804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
# File 'lib/memcache.rb', line 804

def cache_get_multi(server, cache_keys)
  with_socket_management(server) do |socket|
    values = {}
    socket.write "get #{cache_keys}\r\n"

    while keyline = socket.gets do
      return values if keyline == "END\r\n"
      raise_on_error_response! keyline

      unless keyline =~ /\AVALUE (.+) (.+) (.+)/ then
        server.close
        raise MemCacheError, "unexpected response #{keyline.inspect}"
      end

      key, data_length = $1, $3
      values[$1] = socket.read data_length.to_i
      socket.read(2) # "\r\n"
    end

    server.close
    raise MemCacheError, "lost connection to #{server.host}:#{server.port}" # TODO: retry here too
  end
end

#cache_incr(server, cache_key, amount) ⇒ Object

Performs a raw incr for cache_key from server. Returns nil if not found.



832
833
834
835
836
837
838
839
840
841
# File 'lib/memcache.rb', line 832

def cache_incr(server, cache_key, amount)
  with_socket_management(server) do |socket|
    socket.write "incr #{cache_key} #{amount}#{noreply}\r\n"
    break nil if @no_reply
    text = socket.gets
    raise_on_error_response! text
    return nil if text == "NOT_FOUND\r\n"
    return text.to_i
  end
end

#cas(key, expiry = 0, raw = false) ⇒ Object

“cas” is a check and set operation which means “store this data but only if no one else has updated since I last fetched it.” This can be used as a form of optimistic locking.

Works in block form like so:

cache.cas('some-key') do |value|
  value + 1
end

Returns: nil if the value was not found on the memcached server. STORED if the value was updated successfully EXISTS if the value was updated by someone else since last fetch

Raises:



407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
# File 'lib/memcache.rb', line 407

def cas(key, expiry=0, raw=false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  raise MemCacheError, "A block is required" unless block_given?

  (value, token) = gets(key, raw)
  return nil unless value
  updated = yield value
  value = raw ? updated : Marshal.dump(updated)

  with_server(key) do |server, cache_key|
    logger.debug { "cas #{key} to #{server.inspect}: #{value.to_s.bytesize}" } if logger
    command = "cas #{cache_key} 0 #{expiry} #{value.to_s.bytesize} #{token}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result

      if result.nil?
        server.close
        raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
      end

      result
    end
  end
end

#check_multithread_status!Object



955
956
957
958
959
960
961
962
963
964
965
966
# File 'lib/memcache.rb', line 955

def check_multithread_status!
  return if @multithread
  return if @evented

  if Thread.current[:memcache_client] != self.object_id
    raise MemCacheError, <<-EOM
      You are accessing this memcache-client instance from multiple threads but have not enabled multithread support.
      Normally:  MemCache.new(['localhost:11211'], :multithread => true)
      In Rails:  config.cache_store = [:mem_cache_store, 'localhost:11211', { :multithread => true }]
    EOM
  end
end

#create_continuum_for(servers) ⇒ Object



936
937
938
939
940
941
942
943
944
945
946
947
948
949
# File 'lib/memcache.rb', line 936

def create_continuum_for(servers)
  total_weight = servers.inject(0) { |memo, srv| memo + srv.weight }
  continuum = []

  servers.each do |server|
    entry_count_for(server, servers.size, total_weight).times do |idx|
      hash = Digest::SHA1.hexdigest("#{server.host}:#{server.port}:#{idx}")
      value = Integer("0x#{hash[0..7]}")
      continuum << Continuum::Entry.new(value, server)
    end
  end

  continuum.sort { |a, b| a.value <=> b.value }
end

#decr(key, amount = 1) ⇒ Object

Decrements the value for key by amount and returns the new value. key must already exist. If key is not an integer, it is assumed to be

  1. key can not be decremented below 0.



238
239
240
241
242
243
244
245
# File 'lib/memcache.rb', line 238

def decr(key, amount = 1)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    cache_decr server, cache_key, amount
  end
rescue TypeError => err
  handle_error nil, err
end

#delete(key, expiry = 0) ⇒ Object

Removes key from the cache. expiry is ignored as it has been removed from the latest memcached version.

Raises:



526
527
528
529
530
531
532
533
534
535
536
537
538
# File 'lib/memcache.rb', line 526

def delete(key, expiry = 0)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    with_socket_management(server) do |socket|
      logger.debug { "delete #{cache_key} on #{server}" } if logger
      socket.write "delete #{cache_key}#{noreply}\r\n"
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#entry_count_for(server, total_servers, total_weight) ⇒ Object



951
952
953
# File 'lib/memcache.rb', line 951

def entry_count_for(server, total_servers, total_weight)
  ((total_servers * Continuum::POINTS_PER_SERVER * server.weight) / Float(total_weight)).floor
end

#fetch(key, expiry = 0, raw = false) ⇒ Object

Performs a get with the given key. If the value does not exist and a block was given, the block will be called and the result saved via add.

If you do not provide a block, using this method is the same as using get.



271
272
273
274
275
276
277
278
279
280
# File 'lib/memcache.rb', line 271

def fetch(key, expiry = 0, raw = false)
  value = get(key, raw)

  if value.nil? && block_given?
    value = yield
    add(key, value, expiry, raw)
  end

  value
end

#flush_all(delay = 0) ⇒ Object

Flush the cache from all memcache servers. A non-zero value for delay will ensure that the flush is propogated slowly through your memcached server farm. The Nth server will be flushed N*delay seconds from now, asynchronously so this method returns quickly. This prevents a huge database spike due to a total flush all at once.

Raises:



549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
# File 'lib/memcache.rb', line 549

def flush_all(delay=0)
  raise MemCacheError, 'No active servers' unless active?
  raise MemCacheError, "Update of readonly cache" if @readonly

  begin
    delay_time = 0
    @servers.each do |server|
      with_socket_management(server) do |socket|
        logger.debug { "flush_all #{delay_time} on #{server}" } if logger
        if delay == 0 # older versions of memcached will fail silently otherwise
          socket.write "flush_all#{noreply}\r\n"
        else
          socket.write "flush_all #{delay_time}#{noreply}\r\n"
        end
        break nil if @no_reply
        result = socket.gets
        raise_on_error_response! result
        result
      end
      delay_time += delay
    end
  rescue IndexError => err
    handle_error nil, err
  end
end

#get(key, raw = false) ⇒ Object Also known as: []

Retrieves key from memcache. If raw is false, the value will be unmarshalled.



251
252
253
254
255
256
257
258
259
260
261
# File 'lib/memcache.rb', line 251

def get(key, raw = false)
  with_server(key) do |server, cache_key|
    logger.debug { "get #{key} from #{server.inspect}" } if logger
    value = cache_get server, cache_key
    return nil if value.nil?
    value = Marshal.load value unless raw
    return value
  end
rescue TypeError => err
  handle_error nil, err
end

#get_multi(*keys) ⇒ Object

Retrieves multiple values from memcached in parallel, if possible.

The memcached protocol supports the ability to retrieve multiple keys in a single request. Pass in an array of keys to this method and it will:

  1. map the key to the appropriate memcached server

  2. send a single request to each server that has one or more key values

Returns a hash of values.

cache["a"] = 1
cache["b"] = 2
cache.get_multi "a", "b" # => { "a" => 1, "b" => 2 }

Note that get_multi assumes the values are marshalled. You can pass in :raw => true to bypass value marshalling.

cache.get_multi('a', 'b', ..., :raw => true)


303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
# File 'lib/memcache.rb', line 303

def get_multi(*keys)
  raise MemCacheError, 'No active servers' unless active?

  opts = keys.last.is_a?(Hash) ? keys.pop : {}

  keys.flatten!
  key_count = keys.length
  cache_keys = {}
  server_keys = Hash.new { |h,k| h[k] = [] }

  # map keys to servers
  keys.each do |key|
    server, cache_key = request_setup key
    cache_keys[cache_key] = key
    server_keys[server] << cache_key
  end

  results = {}
  raw = opts[:raw] || false
  server_keys.each do |server, keys_for_server|
    keys_for_server_str = keys_for_server.join ' '
    begin
      values = cache_get_multi server, keys_for_server_str
      values.each do |key, value|
        results[cache_keys[key]] = raw ? value : Marshal.load(value)
      end
    rescue IndexError => e
      # Ignore this server and try the others
      logger.warn { "Unable to retrieve #{keys_for_server.size} elements from #{server.inspect}: #{e.message}"} if logger
    end
  end

  return results
rescue TypeError => err
  handle_error nil, err
end

#get_server_for_key(key, options = {}) ⇒ Object

Pick a server to handle the request based on a hash of the key.

Raises:

  • (ArgumentError)


705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
# File 'lib/memcache.rb', line 705

def get_server_for_key(key, options = {})
  raise ArgumentError, "illegal character in key #{key.inspect}" if
    key =~ /\s/
  raise ArgumentError, "key cannot be blank" if key.nil? || key.strip.size == 0
  raise ArgumentError, "key too long #{key.inspect}" if key.length > 250
  raise MemCacheError, "No servers available" if @servers.empty?
  return @servers.first if @servers.length == 1

  hkey = hash_for(key)

  20.times do |try|
    entryidx = Continuum.binary_search(@continuum, hkey)
    server = @continuum[entryidx].server
    return server if server.alive?
    break unless failover
    hkey = hash_for "#{try}#{key}"
  end

  raise MemCacheError, "No servers available"
end

#gets(key, raw = false) ⇒ Object



769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
# File 'lib/memcache.rb', line 769

def gets(key, raw = false)
  with_server(key) do |server, cache_key|
    logger.debug { "gets #{key} from #{server.inspect}" } if logger
    result = with_socket_management(server) do |socket|
      socket.write "gets #{cache_key}\r\n"
      keyline = socket.gets # "VALUE <key> <flags> <bytes> <cas token>\r\n"

      if keyline.nil? then
        server.close
        raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
      end

      raise_on_error_response! keyline
      return nil if keyline == "END\r\n"

      unless keyline =~ /(\d+) (\w+)\r/ then
        server.close
        raise MemCacheError, "unexpected response #{keyline.inspect}"
      end
      value = socket.read $1.to_i
      socket.read 2 # "\r\n"
      socket.gets   # "END\r\n"
      [value, $2]
    end
    result[0] = Marshal.load result[0] unless raw
    result
  end
rescue TypeError => err
  handle_error nil, err
end

#handle_error(server, error) ⇒ Object

Handles error from server.



907
908
909
910
911
912
913
# File 'lib/memcache.rb', line 907

def handle_error(server, error)
  raise error if error.is_a?(MemCacheError)
  server.close if server && server.status == "CONNECTED"
  new_error = MemCacheError.new error.message
  new_error.set_backtrace error.backtrace
  raise new_error
end

#hash_for(key) ⇒ Object

Returns an interoperable hash value for key. (I think, docs are sketchy for down servers).



698
699
700
# File 'lib/memcache.rb', line 698

def hash_for(key)
  Zlib.crc32(key)
end

#incr(key, amount = 1) ⇒ Object

Increments the value for key by amount and returns the new value. key must already exist. If key is not an integer, it is assumed to be 0.



345
346
347
348
349
350
351
352
# File 'lib/memcache.rb', line 345

def incr(key, amount = 1)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    cache_incr server, cache_key, amount
  end
rescue TypeError => err
  handle_error nil, err
end

#inspectObject

Returns a string representation of the cache object.



187
188
189
190
# File 'lib/memcache.rb', line 187

def inspect
  "<MemCache: %d servers, ns: %p, ro: %p>" %
    [@servers.length, @namespace, @readonly]
end

#key_length(key) ⇒ Object

Calculate length of the key, including the namespace and namespace-separator.



690
691
692
# File 'lib/memcache.rb', line 690

def key_length(key)
  key.length + (namespace.nil? ? 0 : ( namespace.length + (@namespace_separator.nil? ? 0 : @namespace_separator.length) ) )
end

#make_cache_key(key) ⇒ Object

Create a key for the cache, incorporating the namespace qualifier if requested.



675
676
677
678
679
680
681
682
683
684
685
# File 'lib/memcache.rb', line 675

def make_cache_key(key)
  if @autofix_keys && (key =~ /\s/ || key_length(key) > 250)
    key = "#{Digest::SHA1.hexdigest(key)}-autofixed"
  end

  if namespace.nil?
    key
  else
    "#{@namespace}#{@namespace_separator}#{key}"
  end
end

#noreplyObject



915
916
917
# File 'lib/memcache.rb', line 915

def noreply
  @no_reply ? ' noreply' : ''
end

#prepend(key, value) ⇒ Object

Prepend - 'add this data to an existing key before existing data' Please note the value is always passed to memcached as raw since it doesn't make a lot of sense to concatenate marshalled data together.

Raises:



506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
# File 'lib/memcache.rb', line 506

def prepend(key, value)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    logger.debug { "prepend #{key} to #{server}: #{value ? value.to_s.bytesize : 'nil'}" } if logger
    command = "prepend #{cache_key} 0 0 #{value.to_s.bytesize}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#raise_on_error_response!(response) ⇒ Object



930
931
932
933
934
# File 'lib/memcache.rb', line 930

def raise_on_error_response!(response)
  if response =~ /\A(?:CLIENT_|SERVER_)?ERROR(.*)/
    raise MemCacheError, $1.strip
  end
end

#readonly?Boolean

Returns whether or not the cache object was created read only.

Returns:

  • (Boolean)


202
203
204
# File 'lib/memcache.rb', line 202

def readonly?
  @readonly
end

#replace(key, value, expiry = 0, raw = false) ⇒ Object

Add key to the cache with value value that expires in expiry seconds, but only if key already exists in the cache. If raw is true, value will not be Marshalled.

Raises:



465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
# File 'lib/memcache.rb', line 465

def replace(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  value = Marshal.dump value unless raw
  with_server(key) do |server, cache_key|
    logger.debug { "replace #{key} to #{server}: #{value ? value.to_s.bytesize : 'nil'}" } if logger
    command = "replace #{cache_key} 0 #{expiry} #{value.to_s.bytesize}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#request_setup(key) ⇒ Object

Performs setup for making a request with key from memcached. Returns the server to fetch the key from and the complete key to use.

Raises:



923
924
925
926
927
928
# File 'lib/memcache.rb', line 923

def request_setup(key)
  raise MemCacheError, 'No active servers' unless active?
  cache_key = make_cache_key key
  server = get_server_for_key cache_key
  return server, cache_key
end

#resetObject

Reset the connection to all memcache servers. This should be called if there is a problem with a cache lookup that might have left the connection in a corrupted state.



580
581
582
# File 'lib/memcache.rb', line 580

def reset
  @servers.each { |server| server.close }
end

#set(key, value, expiry = 0, raw = false) ⇒ Object

Raises:



363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
# File 'lib/memcache.rb', line 363

def set(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly

  value = Marshal.dump value unless raw
  with_server(key) do |server, cache_key|
    logger.debug { "set #{key} to #{server.inspect}: #{value.to_s.bytesize}" } if logger

    if @check_size && value.to_s.bytesize > ONE_MB
      raise MemCacheError, "Value too large, memcached can only store 1MB of data per key"
    end

    with_socket_management(server) do |socket|
      socket.write "set #{cache_key} 0 #{expiry} #{value.to_s.bytesize}#{noreply}\r\n"
      socket.write value.to_s
      socket.write "\r\n"
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result

      if result.nil?
        server.close
        raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
      end

      result
    end
  end
end

#statsObject

Returns statistics for each memcached server. An explanation of the statistics can be found in the memcached docs:

code.sixapart.com/svn/memcached/trunk/server/doc/protocol.txt

Example:

>> pp CACHE.stats
{"localhost:11211"=>
  {"bytes"=>4718,
   "pid"=>20188,
   "connection_structures"=>4,
   "time"=>1162278121,
   "pointer_size"=>32,
   "limit_maxbytes"=>67108864,
   "cmd_get"=>14532,
   "version"=>"1.2.0",
   "bytes_written"=>432583,
   "cmd_set"=>32,
   "get_misses"=>0,
   "total_connections"=>19,
   "curr_connections"=>3,
   "curr_items"=>4,
   "uptime"=>1557,
   "get_hits"=>14532,
   "total_items"=>32,
   "rusage_system"=>0.313952,
   "rusage_user"=>0.119981,
   "bytes_read"=>190619}}
=> nil

Raises:



616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
# File 'lib/memcache.rb', line 616

def stats
  raise MemCacheError, "No active servers" unless active?
  server_stats = {}

  @servers.each do |server|
    next unless server.alive?

    with_socket_management(server) do |socket|
      value = nil
      socket.write "stats\r\n"
      stats = {}
      while line = socket.gets do
        raise_on_error_response! line
        break if line == "END\r\n"
        if line =~ /\ASTAT ([\S]+) ([\w\.\:]+)/ then
          name, value = $1, $2
          stats[name] = case name
                        when 'version'
                          value
                        when 'rusage_user', 'rusage_system' then
                          seconds, microseconds = value.split(/:/, 2)
                          microseconds ||= 0
                          Float(seconds) + (Float(microseconds) / 1_000_000)
                        else
                          if value =~ /\A\d+\Z/ then
                            value.to_i
                          else
                            value
                          end
                        end
        end
      end
      server_stats["#{server.host}:#{server.port}"] = stats
    end
  end

  raise MemCacheError, "No active servers" if server_stats.empty?
  server_stats
end

#with_server(key) ⇒ Object



888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
# File 'lib/memcache.rb', line 888

def with_server(key)
  retried = false
  begin
    server, cache_key = request_setup(key)
    yield server, cache_key
  rescue IndexError => e
    logger.warn { "Server failed: #{e.class.name}: #{e.message}" } if logger
    if !retried && @servers.size > 1
      logger.info { "Connection to server #{server.inspect} DIED! Retrying operation..." } if logger
      retried = true
      retry
    end
    handle_error(nil, e)
  end
end

#with_socket_management(server, &block) ⇒ Object

Gets or creates a socket connected to the given server, and yields it to the block, wrapped in a mutex synchronization if @multithread is true.

If a socket error (SocketError, SystemCallError, IOError) or protocol error (MemCacheError) is raised by the block, closes the socket, attempts to connect again, and retries the block (once). If an error is again raised, reraises it as MemCacheError.

If unable to connect to the server (or if in the reconnect wait period), raises MemCacheError. Note that the socket connect code marks a server dead for a timeout period, so retrying does not apply to connection attempt failures (but does still apply to unexpectedly lost connections etc.).



857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
# File 'lib/memcache.rb', line 857

def with_socket_management(server, &block)
  check_multithread_status!

  @mutex.lock if @multithread
  retried = false

  begin
    socket = server.socket

    # Raise an IndexError to show this server is out of whack. If were inside
    # a with_server block, we'll catch it and attempt to restart the operation.

    raise IndexError, "No connection to server (#{server.status})" if socket.nil?

    block.call(socket)

  rescue SocketError, Errno::EAGAIN, Timeout::Error => err
    logger.warn { "Socket failure: #{err.message}" } if logger
    server.mark_dead(err)
    handle_error(server, err)

  rescue MemCacheError, SystemCallError, IOError => err
    logger.warn { "Generic failure: #{err.class.name}: #{err.message}" } if logger
    handle_error(server, err) if retried || socket.nil?
    retried = true
    retry
  end
ensure
  @mutex.unlock if @multithread
end