memcached
is a fully featured Memcached client for Node.js. memcached
is
build with scaling, high availability and exceptional performance in mind. We
use consistent hashing to store the data across different nodes. Consistent
hashing is a scheme that provides a hash table functionality in a way that
adding or removing a server node does not significantly change the mapping of
the keys to server nodes. The algorithm that is used for consistent hashing is
the same as libketama
.
There are different ways to handle errors for example, when a server becomes
unavailable you can configure the client to see all requests to that server as
cache misses until it goes up again. It's also possible to automatically remove
the affected server from the consistent hashing algorithm or provide memcached
with a failover server that can take the place of the unresponsive server.
When these issues occur the memcached
client will emit different events where
you can subscribe to containing detailed information about the issues.
The client is configurable on different levels. There's a global configuration
that you update so all you Memcached clusters will use the same failure
configuration for example, but it's also possible to overwrite these changes per
memcached
instance.
This module uses the ASCII protocol to communicate with the server, this makes it easier to debug for you are user as you can see what is send over the wire but also for me as developer. But this also means that SASL auth is not supported in this driver as that requires the use of the binary protocol. The ASCII protocol not only used by memcached but also by other databases and message queues, so that is a nice extra.
The constructor of the memcached
client take 2 different arguments server locations
and options
. Syntax:
var Memcached = require('memcached');
var memcached = new Memcached(Server locations, options);
The server locations is designed to work with different formats. These formats are all internally parsed to the correct format so our consistent hashing scheme can work with it. You can either use:
-
String, this only works if you have are running a single server instance of Memcached. It's as easy a suppling a string in the following format:
hostname:port
. For example192.168.0.102:11212
This would tell the client to connect to host192.168.0.102
on port number11212
. -
Array, if you are running a single server you would only have to supply one item in the array. The array format is particularly useful if you are running a cluster of Memcached servers. This will allow you to spread the keys and load between the different servers. Giving you higher availability for when one of your Memcached servers goes down.
-
Object, when you are running a cluster of Memcached servers it could happen to not all server can allocate the same amount of memory. You might have a Memcached server with 128mb, 512, 128mb. If you would the array structure all servers would have the same weight in the consistent hashing scheme. Spreading the keys 33/33/33 over the servers. But as server 2 has more memory available you might want to give it more weight so more keys get stored on that server. When you are using a object, the
key
should represent the server location syntax and the value the weight of the server. By default all servers have a weight of 1.{ '192.168.0.102:11212': 1, '192.168.0.103:11212': 2, '192.168.0.104:11212': 1 }
would generate a 25/50/25 distribution of the keys.
If you would implement one of the above formats, your constructor would something like this:
var memcached = new Memcached({ '192.168.0.102:11212': 1, '192.168.0.103:11212': 2, '192.168.0.104:11212': 1 });
var memcached = new Memcached([ '192.168.0.102:11212', '192.168.0.103:11212', '192.168.0.104:11212' ]);
var memcached = new Memcached('192.168.0.102:11212');
There 2 kinds of options that can be configured. A global configuration that
will be inherited by all Memcached servers instances and a client specific
configuration that can be used to overwrite the globals. The options should be
formatted in an JavaScript object
. They both use the same object structure:
maxKeySize
: 250, the max size of they key allowed by the Memcached server.maxExpiration
: 2592000, the max expiration of keys by the Memcached server in milliseconds.maxValue
: 1048576, the max size of a value that is allowed by the Memcached server.poolSize
: 10, the maximum connections we can allocate in our connection pool.algorithm
: crc32, the hashing algorithm that should be used to generate the hashRing values.reconnect
: 18000000, when the server is marked as dead we will attempt to reconnect every x milliseconds.timeout
: 5000, after x ms the server should send a timeout if we can't connect. This will also be used close the connection if we are idle.retries
: 5, amount of tries before we mark the server as dead.retry
: 30000, timeout between each retry in x milliseconds.remove
: false, when the server is marked as dead you can remove it from the pool so all other will receive the keys instead.failOverServers
: undefined, the ability use these servers as failover when the dead server get's removed from the consistent hashing scheme. This must be an array of servers confirm the server_locations specification.keyCompression
: true, compress keys using md5 if they exceed the maxKeySize option.
Example usage:
var memcached = new Memcached('localhost:11212', {retries:10,retry:10000,remove:true,failOverServers:['192.168.0.103:11212']});
If you wish to configure the options globally:
var Memcached = require('memcached');
// all global configurations should be applied to the .config object of the Client.
Memcached.config.poolSize = 25;
Touches the given key.
Arguments
key
: String The key
lifetime
: Number After how long should the key expire.
callback
: Function
memcached.touch('key', 10, function (err) {
// stuff
});
Get the value for the given key.
Arguments
key
: String, the key
callback
: Function, the callback.
memcached.get('foo', function (err, data) {
console.log(data);
});
Get the value and the CAS id.
Arguments
key
: String, the key
callback
: Function, the callback.
memcached.gets('foo', function (err, data) {
console.log(data.foo);
console.log(data.cas);
// Please note that the data is stored under the name of the given key.
});
Retrieves a bunch of values from multiple keys.
Arguments
keys
: Array, all the keys that needs to be fetched
callback
: Function, the callback.
memcached.getMulti(['foo', 'bar'], function (err, data) {
console.log(data.foo);
console.log(data.bar);
});
Stores a new value in Memcached.
Arguments
key
: String the name of the key
lifetime
: Number, how long the data needs to be stored
value
: Mixed Either a buffer, JSON, number or string that you want to store.
callback
: Function the callback
memcached.set('foo', 10, 'bar', function (err) {
// stuff
});
Replaces the value in memcached.
Arguments
key
: String the name of the key
lifetime
: Number, how long the data needs to be replaced
value
: Mixed Either a buffer, JSON, number or string that you want to store.
callback
: Function the callback
memcached.replaces('foo', 10, 'bar', function (err) {
// stuff
});
Add the value, only if it's in memcached already.
Arguments
key
: String the name of the key
lifetime
: Number, how long the data needs to be replaced
value
: Mixed Either a buffer, JSON, number or string that you want to store.
callback
: Function the callback
memcached.add('foo', 10, 'bar', function (err) {
// stuff
});
Add the value, only if it matches the given CAS value.
Arguments
key
: String the name of the key
value
: Mixed Either a buffer, JSON, number or string that you want to store.
lifetime
: Number, how long the data needs to be replaced
cas
: String the CAS value
callback
: Function the callback
memcached.gets('foo', function (err, data) {
memcached.cas('foo', 'bar', data.cas, 10, function (err) {
// stuff
});
});
Add the given value string to the value of an existing item.
Arguments
key
: String the name of the key
value
: Mixed Either a buffer, JSON, number or string that you want to store.
callback
: Function the callback
memcached.append('foo', 'bar', function (err) {
// stuff
});
Add the given value string to the value of an existing item.
Arguments
key
: String the name of the key
value
: Mixed Either a buffer, JSON, number or string that you want to store.
callback
: Function the callback
memcached.preprend('foo', 'bar', function (err) {
// stuff
});
Increment a given key.
Arguments
key
: String the name of the key
amount
: Number The incremention
callback
: Function the callback
memcached.incr('foo', 10, function (err) {
// stuff
});
Decrement a given kehy.
Arguments
key
: String the name of the key
amount
: Number The incremention
callback
: Function the callback
memcached.incr('foo', 10, function (err) {
// stuff
});
Remove the key from memcached.
Arguments
key
: String the name of the key
callback
: Function the callback
memcached.del('foo', function (err) {
// stuff
});
Retrieves the version number of your server.
Flushes the memcached server.
Retrieves stats from your memcached server.
Retrieves your stats settings
.
Retrieves stats slabs
information.
Retrieves stats items
information.
Inspect cache, see examples for a detailed explaination.
Closes all active memcached connections.
The following methods are intended for private usage:
Fetches or generates a connection for the given server. The supplied callback function will receive a reference to the connection as argument. If there are issues with the server connection, we are going to respond with cache-miss pattern.
Arguments
server
: String, The server that needs a connection, the format must be
confirm the server_locations specification.
callback
: Function, The callback function that receives the net.Stream
connection. It will be called with 2 arguments error
and connection
.
Example:
memcached.connect( '192.168.0.103:11212', function( err, conn ){
if( err ) throw new Error( err );
console.log( conn.server );
});
A small wrapper function that makes it easier to query multiple Memcached servers. It will return the location for each key or the complete list of servers.
Arguments
keys
: Array (optional), They keys that needs to be converted to a server.
callback
: Function, The callback function for the data, it will be called
for each key. It will be called with 4 arguments:
server
: String, The server location.key
: String, The key associated with the server, if you didn't specify keys, this variable will be undefined.index
: Number, The current index of the looptotal
: Number, The total amount server retrieved.
Example:
memcached.multi( false, function( server, key, index, totals ){
if( err ) throw new Error( err );
this.connect( server, function( err, conn ){
console.log( "connection ready" )
})
});
This is the core functionality of the memcached
client. All public API's are
routed through this function. It takes care of the argument validations Server
retrieval ( If the server argument isn't specified ). After all data ready a
connection is asked for the private connect
method and the command is written
to the Memcached server.
Arguments
query
: Object, The metaData object, see the Callbacks
section for the
specification.
server
: String, The server the to connect. This is only needed when the
metaData object doesn't contain a key property to retrieve the server from.
Example:
memcached.command({
key: 'key', callback: function(){ console.dir( arguments ); },
// validate the arguments
validate: [[ 'key', String ], [ 'callback', Function ]],
// used for the query
type: 'delete',
command: 'delete key'
});
A internal function for logging issues with connections. As there can be various
of ways that an error occurs we need solid issue manager to handle all these
cases. For example server could crash or the Memcached server could respond with
SERVER ERROR <broken>
.
Arguments
error
: String, The actual error message.
Stream
: net.Stream, A reference to the connection stream where the error
occurred on.
callback
: Function (optional), The callback function of a potential
request, it will be marked as cache miss if it was provided
Example:
memcached.connectionIssue( "Server down", connectionReference );
Each method requires a callback function. Once this function get executed there will be 2 variables applied:
error
: A error response if something went wrong while retrieving data from the Memcached server. Depending on the type of request this will either be an string or an Array with multiple errors.response
: The actual result from the Memcached server. If the response isfalse
orundefined
than a cache miss occurred. Cache misses will also occur when there is an error. So you might want to check on errors first.
When we have a successful response, the context of the callback function will shift to a metaData object. The metaData object contains all information that we used to generate the request for the Memcached server. The metaData object contains the following properties:
start
: Date in milliseconds when the request was receivedexecution
: Total execution time for the request, including response parsing.callback
: Reference to the callback functiontype
: The type of Memcached commandcommand
: The compiled command that was send through the socketsvalidate
: The properties of metaData object that needs type validation.
And all the arguments you have send to the method, this depends on the method you have called.
When connection issues occur we send out different notifications using the
EventEmitter
protocol. This can be useful for logging, notification and
debugging purposes. Each event will receive details Object containing detailed
information about the issues that occurred.
The details Object contains the various of error messages that caused, the following 3 will always be present in all error events:
server
: the server where the issue occurred ontokens
: a array of the parsed server string in[port, hostname]
format.messages
: a array containing all error messages that this server received. As messages are added to the array using .push(), the first issue will at the beginning and the latest error at the end of the array.
The following properties depend on the type of event that is send. If we are still in our retry phase the details will also contain:
retries
: the amount of retries left before we mark the server as dead.totalRetries
: the total amount of retries we did on this server, as when the server has been reconnected after it's dead theretries
will be rest to defaults and messages will be removed.
If the server is dead these details will be added:
totalReconnectsAttempted
: the total reconnects we have attempted. This is the success and failure combined.totalReconnectsSuccess
: the total successful reconnects we have made.totalReconnectsFailed
: the total failed reconnects we have made.totalDownTime
: the total down time that was generated. Formula: ( totalReconnectsFailed * reconnect_timeout ) + ( totalRetries * retry_timeout).
There are 5
different events that the memcached
client emits when connection
issues occur.
issue
: a issue occurred on one a server, we are going to attempt a retry next.failure
: a server has been marked as failure or dead.reconnecting
: we are going to attempt to reconnect the to the failed server.reconnected
: successfully reconnected to the memcached server.remove
: removing the server from our consistent hashing.
Example implementations:
var memcached = new Memcached([ '192.168.0.102:11212', '192.168.0.103:11212' ]);
memcached.on('failure', function( details ){ sys.error( "Server " + details.server + "went down due to: " + details.messages.join( '' ) ) });
memcached.on('reconnecting', function( details ){ sys.debug( "Total downtime caused by server " + details.server + " :" + details.totalDownTime + "ms")});