Class: MemCache

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

Overview

approaching a complete implementation.

Defined Under Namespace

Classes: ContinuumEntry, MemCacheError, Server

Constant Summary collapse

VERSION =

The version of MemCache you are using.

'1.5.0.7'
DEFAULT_OPTIONS =

Default options for the cache object.

{
  :namespace   => nil,
  :readonly    => false,
  :multithread => false,
}
DEFAULT_PORT =

Default memcached port.

11211
DEFAULT_WEIGHT =

Default memcached server weight.

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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.

Other options are ignored.



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

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

  opts = DEFAULT_OPTIONS.merge opts
  @namespace   = opts[:namespace]
  @readonly    = opts[:readonly]
  @multithread = opts[:multithread]
  @mutex       = Mutex.new if @multithread
  @buckets     = []
  self.servers = servers
end

Instance Attribute Details

#multithread ⇒ Object (readonly)

The multithread setting for this instance



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# File 'lib/memcache.rb', line 58

def multithread
  @multithread
end

#namespace ⇒ Object (readonly)

The namespace for this instance



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# File 'lib/memcache.rb', line 53

def namespace
  @namespace
end

#request_timeout ⇒ Object

The amount of time to wait for a response from a memcached server. If a response is not completed within this time, the connection to the server will be closed and an error will be raised.



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# File 'lib/memcache.rb', line 48

def request_timeout
  @request_timeout
end

#servers ⇒ Object

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



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# File 'lib/memcache.rb', line 63

def servers
  @servers
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.



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# File 'lib/memcache.rb', line 428

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

#active? ⇒ Boolean

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

Returns:

  • (Boolean) 


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

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 or MemCache#[]=.

Raises:



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# File 'lib/memcache.rb', line 284

def add(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    value = Marshal.dump value unless raw
    command = "add #{cache_key} 0 #{expiry} #{value.size}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#binary_search(ary, value, &block) ⇒ Object

Find the closest element in Array less than or equal to value.



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# File 'lib/memcache.rb', line 821

def binary_search(ary, value, &block)
  upper = ary.size - 1
  lower = 0
  idx = 0

  result = while(lower <= upper) do
    idx = (lower + upper) / 2
    comp = block.call(ary[idx]) <=> value
 
    if comp == 0
      break idx
    elsif comp > 0
      upper = idx - 1
    else
      lower = idx + 1
    end
  end
  result ? ary[result] : ary[upper]
end

#cache_decr(server, cache_key, amount) ⇒ Object

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



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# File 'lib/memcache.rb', line 480

def cache_decr(server, cache_key, amount)
  with_socket_management(server) do |socket|
    socket.write "decr #{cache_key} #{amount}\r\n"
    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.



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# File 'lib/memcache.rb', line 494

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.



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# File 'lib/memcache.rb', line 521

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.



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# File 'lib/memcache.rb', line 549

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

#create_continuum_for(servers) ⇒ Object 



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# File 'lib/memcache.rb', line 636

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 << ContinuumEntry.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.



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# File 'lib/memcache.rb', line 163

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 in expiry seconds.

Raises:



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# File 'lib/memcache.rb', line 302

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|
      socket.write "delete #{cache_key} #{expiry}\r\n"
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#entry_count_for(server, total_servers, total_weight) ⇒ Object 



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# File 'lib/memcache.rb', line 651

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

#flush_all ⇒ Object

Flush the cache from all memcache servers.

Raises:



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# File 'lib/memcache.rb', line 317

def flush_all
  raise MemCacheError, 'No active servers' unless active?
  raise MemCacheError, "Update of readonly cache" if @readonly

  begin
    @mutex.lock if @multithread
    @servers.each do |server|
      with_socket_management(server) do |socket|
        socket.write "flush_all\r\n"
        result = socket.gets
        raise_on_error_response! result
        result
      end
    end
  rescue IndexError => err
    handle_error nil, err
  ensure
    @mutex.unlock if @multithread
  end
end

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

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



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# File 'lib/memcache.rb', line 176

def get(key, raw = false)
  with_server(key) do |server, cache_key|
    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 }



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

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

  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 = {}

  server_keys.each do |server, keys_for_server|
    keys_for_server = keys_for_server.join ' '
    values = cache_get_multi server, keys_for_server
    values.each do |key, value|
      results[cache_keys[key]] = Marshal.load value
    end
  end

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

#get_server_for_key(key) ⇒ Object

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

Raises:

  • (ArgumentError) 


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# File 'lib/memcache.rb', line 457

def get_server_for_key(key)
  raise ArgumentError, "illegal character in key #{key.inspect}" if
    key =~ /\s/
  # 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
  key = Digest::MD5.hexdigest(key) if key.length > 250

  hkey = hash_for(key)

  20.times do |try|
    server = binary_search(@continuum, hkey) { |e| e.value }.server
    return server if server.alive?
    hkey = hash_for "#{try}#{key}"
  end

  raise MemCacheError, "No servers available"
end

#handle_error(server, error) ⇒ Object

Handles error from server.



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# File 'lib/memcache.rb', line 611

def handle_error(server, error)
  raise error if error.is_a?(MemCacheError)
  server.close if server
  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).



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# File 'lib/memcache.rb', line 450

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.



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# File 'lib/memcache.rb', line 238

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

#inspect ⇒ Object

Returns a string representation of the cache object.



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# File 'lib/memcache.rb', line 109

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

#make_cache_key(key) ⇒ Object

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



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# File 'lib/memcache.rb', line 438

def make_cache_key(key)
  if namespace.nil? then
    key
  else
    "#{@namespace}:#{key}"
  end
end

#raise_on_error_response!(response) ⇒ Object 



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# File 'lib/memcache.rb', line 630

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) 


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# File 'lib/memcache.rb', line 124

def readonly?
  @readonly
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:



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# File 'lib/memcache.rb', line 623

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

#reset ⇒ Object

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.



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# File 'lib/memcache.rb', line 343

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

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

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.

Raises:



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# File 'lib/memcache.rb', line 254

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

    value = Marshal.dump value unless raw
    command = "set #{cache_key} 0 #{expiry} #{value.to_s.size}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      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

#stats ⇒ Object

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:



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# File 'lib/memcache.rb', line 379

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 ([\w]+) ([\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 



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# File 'lib/memcache.rb', line 593

def with_server(key)
  retried = false
  begin
    server, cache_key = request_setup(key)
    yield server, cache_key
  rescue IndexError => e
    if !retried && @servers.size > 1
      puts "Connection to server #{server.inspect} DIED! Retrying operation..."
      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.).



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# File 'lib/memcache.rb', line 573

def with_socket_management(server, &block)
  @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 MemCacheError, SocketError, SystemCallError, IOError => err
    handle_error(server, err) if retried || socket.nil?
    retried = true
    retry
  end
ensure
  @mutex.unlock if @multithread
end