Couchbase Ruby Client

This is the official client library for use with Couchbase Server. There are related libraries available:


If you found an issue, please file it in our JIRA. Also you are always welcome on #libcouchbase channel at IRC servers.



This gem depends libcouchbase. In most cases installing libcouchbase doesn't take much effort.

MacOS (Homebrew)

$ brew install libcouchbase

The official homebrew repository contains only stable versions of libvbucket and libcouchbase, if you need preview, take a look at Couchbase's fork:

$ brew install

Debian (Ubuntu)

Add the appropriate line to /etc/apt/sources.list.d/couchbase.list for your OS release:

# Ubuntu 11.10 Oneiric Ocelot (Debian unstable)
deb oneiric oneiric/main

# Ubuntu 10.04 Lucid Lynx (Debian stable or testing)
deb lucid lucid/main

Import Couchbase PGP key:

wget -O- | sudo apt-key add -

Then install them

$ sudo apt-get update && sudo apt-get install libcouchbase-dev

Again, if you need preview versions, just use another repositories in your couchbase.list

# Ubuntu 11.10 Oneiric Ocelot (Debian unstable)
deb oneiric oneiric/main

# Ubuntu 10.04 Lucid Lynx (Debian stable or testing)
deb lucid lucid/main

Centos (Redhat and rpm-based systems)

Add these lines to /etc/yum.repos.d/couchbase.repo using the correct architecture

name = Couchbase package repository
baseurl =

name = Couchbase package repository
baseurl =

Then to install libcouchbase itself, run:

$ sudo yum update && sudo yum install libcouchbase-devel

We have preview repositories for RPMs too, use them if you need to try fresh version of couchbase gem:

name = Couchbase package repository
baseurl =

name = Couchbase package repository
baseurl =


There no additional dependencies for Windows systems. The gem carry prebuilt binary for it.

Couchbase gem

Now install the couchbase gem itself

$ gem install couchbase


First of all you need to load library:

require 'couchbase'

There are several ways to establish new connection to Couchbase Server. By default it uses the http://localhost:8091/pools/default/buckets/default as the endpoint. The client will automatically adjust configuration when the cluster will rebalance its nodes when nodes are added or deleted therefore this client is "smart".

c = Couchbase.connect

This is equivalent to following forms:

c = Couchbase.connect("http://localhost:8091/pools/default/buckets/default")
c = Couchbase.connect("http://localhost:8091/pools/default")
c = Couchbase.connect("http://localhost:8091")
c = Couchbase.connect(:hostname => "localhost")
c = Couchbase.connect(:hostname => "localhost", :port => 8091)
c = Couchbase.connect(:pool => "default", :bucket => "default")

The hash parameters take precedence on string URL.

If you worry about state of your nodes or not sure what node is alive, you can pass the list of nodes and the library will iterate over it until finds the working one. From that moment it won't use your list, because node list from cluster config is more actual.

c = Couchbase.connect(:bucket => "mybucket",
                      :node_list => ['','])

There is also handy method Couchbase.bucket which uses thread local storage to keep the reference to default connection. You can set the connection options via Couchbase.connection_options:

Couchbase.connection_options = {:bucket => 'blog'}                   #=> "blog"
Couchbase.bucket.set("foo", "bar")      #=> 3289400178357895424

The library supports both synchronous and asynchronous mode. In asynchronous mode all operations will return control to caller without blocking current thread. You can pass the block to method and it will be called with result when the operation will be completed. You need to run event loop when you scheduled your operations:

c = Couchbase.connect do |conn|
  conn.get("foo") {|ret| puts ret.value}
  conn.set("bar", "baz")

The handlers could be nested do |conn|
  conn.get("foo") do |ret|
    conn.incr(ret.value, :initial => 0)

The asynchronous callback receives instance of Couchbase::Result which responds to several methods to figure out what was happened:

  • success?. Returns true if operation succed.

  • error. Returns nil or exception object (subclass of Couchbase::Error::Base) if something went wrong.

  • key

  • value

  • flags

  • cas. The CAS version tag.

  • node. Node address. It is used in flush and stats commands.

  • operation. The symbol, representing an operation.

To handle global errors in async mode #on_error callback should be used. It can be set in following fashions:

c.on_error do |opcode, key, exc|
  # ...

handler = lambda {|opcode, key, exc| }
c.on_error = handler

By default connection uses :quiet mode. This mean it won't raise exceptions when the given key is not exists:

c.get("missing-key")            #=> nil

It could be useful when you are trying to make you code a bit efficient by avoiding exception handling. (See #add and #replace operations). You can turn on these exception by passing :quiet => false when you are instantiating the connection or change corresponding attribute:

c.quiet = false
c.get("missing-key")                    #=> raise Couchbase::Error::NotFound
c.get("missing-key", :quiet => true)    #=> nil

The library supports three different formats for representing values:

  • :document (default) format supports most of ruby types which could be mapped to JSON data (hashes, arrays, string, numbers). A future version will be able to run map/reduce queries on the values in the document form (hashes)

  • :plain This format avoids any conversions to be applied to your data, but your data should be passed as String. This is useful for building custom algorithms or formats. For example to implement a set:

  • :marshal Use this format if you'd like to transparently serialize your ruby object with standard Marshal.dump and Marshal.load methods

The couchbase API is the superset of Memcached binary protocol, so you can use its operations.


val = c.get("foo")
val, flags, cas = c.get("foo", :extended => true)

Get and touch

val = c.get("foo", :ttl => 10)

Get multiple values. In quiet mode will put nil values on missing positions:

vals = c.get("foo", "bar", "baz")
val_foo, val_bar, val_baz = c.get("foo", "bar", "baz") do
  c.get("foo") do |ret|

Get multiple values with extended information. The result will represented by hash with tuples [value, flags, cas] as a value.

vals = c.get("foo", "bar", "baz", :extended => true)
vals.inspect    #=> {"baz"=>["3", 0, 4784582192793125888],
                     "foo"=>["1", 0, 8835713818674332672],
                     "bar"=>["2", 0, 10805929834096100352]}

Hash-like syntax

c["foo", "bar", "baz"]
c["foo", {:extended => true}]
c["foo", :extended => true]         # for ruby 1.9.x only


c.touch("foo")                      # use :default_ttl
c.touch("foo", 10)
c.touch("foo", :ttl => 10)
c.touch("foo" => 10, "bar" => 20)
c.touch("foo" => 10, "bar" => 20){|key, success|  }


c.set("foo", "bar")
c.set("foo", "bar", :flags => 0x1000, :ttl => 30, :format => :plain)
c["foo"] = "bar"
c["foo", {:flags => 0x1000, :format => :plain}] = "bar"
c["foo", :flags => 0x1000] = "bar"          # for ruby 1.9.x only
c.set("foo", "bar", :cas => 8835713818674332672)
c.set("foo", "bar"){|cas, key, operation|  }


Add command will fail if the key already exists. It accepts the same options as set command above.

c.add("foo", "bar")
c.add("foo", "bar", :flags => 0x1000, :ttl => 30, :format => :plain)


The replace command will fail if the key already exists. It accepts the same options as set command above.

c.replace("foo", "bar")


These commands are meaningful when you are using the :plain value format, because the concatenation is performed by server which has no idea how to merge to JSON values or values in ruby Marshal format. You may receive an Couchbase::Error::ValueFormat error.

c.set("foo", "world")
c.append("foo", "!")
c.prepend("foo", "Hello, ")
c.get("foo")                    #=> "Hello, world!"


These commands increment the value assigned to the key. It will raise Couchbase::Error::DeltaBadval if the delta or value is not a number.

c.set("foo", 1)
c.incr("foo")                   #=> 2
c.incr("foo", :delta => 2)      #=> 4
c.incr("foo", 4)                #=> 8
c.incr("foo", -1)               #=> 7
c.incr("foo", -100)             #=> 0 do
  c.incr("foo") do |ret|

c.set("foo", 10)
c.decr("foo", 1)                #=> 9
c.decr("foo", 100)              #=> 0 do
  c.decr("foo") do |ret|

c.incr("missing1", :initial => 10)      #=> 10
c.incr("missing1", :initial => 10)      #=> 11
c.incr("missing2", :create => true)     #=> 0
c.incr("missing2", :create => true)     #=> 1

Note that it isn't the same as increment/decrement in ruby, which is performed on client side with following set operation:

c["foo"] = 10
c["foo"] -= 20                  #=> -10


c.delete("foo", :cas => 8835713818674332672)
c.delete("foo", 8835713818674332672) do
  c.delete do |ret|


Flush the items in the cluster.

c.flush do
  c.flush do |ret|


Return statistics from each node in the cluster

c.stats(:memory) do
  c.stats do |ret|

The result is represented as a hash with the server node address as the key and stats as key-value pairs.

      # ...
      # ...
      # ...
  # ...


It is possible to create timers to implement general purpose timeouts. Note that timers are using microseconds for time intervals. For example, following examples increment the keys value five times with 0.5 second interval:

c.set("foo", 100)
n = 1 do
  c.create_periodic_timer(500000) do |tm|
    c.incr("foo") do
      if n == 5
        n += 1

Views (Map/Reduce queries)

If you store structured data, they will be treated as documents and you can handle them in map/reduce function from Couchbase Views. For example, store a couple of posts using memcached API:

c['biking'] = {:title => 'Biking',
               :body => 'My biggest hobby is mountainbiking. The other day...',
               :date => '2009/01/30 18:04:11'}
c['bought-a-cat'] = {:title => 'Bought a Cat',
                     :body => 'I went to the the pet store earlier and brought home a little kitty...',
                     :date => '2009/01/30 20:04:11'}
c['hello-world'] = {:title => 'Hello World',
                    :body => 'Well hello and welcome to my new blog...',
                    :date => '2009/01/15 15:52:20'}

Now let's create design doc with sample view and save it in file 'blog.json':

  "_id": "_design/blog",
  "language": "javascript",
  "views": {
    "recent_posts": {
      "map": "function(doc){if( && doc.title){emit(, doc.title);}}"

This design document could be loaded into the database like this (also you can pass the ruby Hash or String with JSON encoded document):


To execute view you need to fetch it from design document _design/blog:

blog = c.design_docs['blog']
blog.views                    #=> ["recent_posts"]
blog.recent_posts             #=> [#<Couchbase::ViewRow:9855800 @id="hello-world" @key="2009/01/15 15:52:20" @value="Hello World" @doc=nil @meta={} @views=[]>, ...]

Gem uses streaming parser to access view results so you can iterate them easily and if your code won't keep links to the documents GC might free them as soon as it decide they are unreachable, because parser doesn't store global JSON tree.

blog.recent_posts.each do |doc|
  # do something
  # with doc object
  doc.key   # gives the key argument of the emit()
  doc.value # gives the value argument of the emit()

Load with documents

blog.recent_posts(:include_docs => true).each do |doc|
  doc.doc       # gives the document which emitted the item
  doc['date']   # gives the argument of the underlying document

You can also use Enumerator to iterate view results

require 'date'
posts_by_date ={|h,k| h[k] = []}
enum = c.recent_posts(:include_docs => true).each  # request hasn't issued yet
enum.inject(posts_by_date) do |acc, doc|
  acc[date] = Date.strptime(doc['date'], '%Y/%m/%d')

The Couchbase server could generate errors during view execution with 200 OK and partial results. By default the library raises exception as soon as errors detected in the result stream, but you can define the callback on_error to intercept these errors and do something more useful.

view = blog.recent_posts(:include_docs => true)
logger =

view.on_error do |from, reason|
  logger.warn("#{view.inspect} received the error '#{reason}' from #{from}")

posts = view.each do |doc|
  # do something
  # with doc object

Note that errors object in view results usually goes after the rows, so you will likely receive a number of view results successfully before the error is detected.


As far as couchbase gem uses libcouchbase as the backend, you can choose from several asynchronous IO options:

  • :default this one is used by default and implemented as the part of the ruby extensions (this mean you don't need any dependencies apart from libcouchbase2-core and libcouchbase-dev to build and use it). This engine honours ruby GVL, so when it comes to waiting for IO operations from kernel it release the GVL allowing interpreter to run your code. This technique isn't available on windows, but down't worry :default engine still accessible and will pick up statically linked on that platform :libevent engine.

  • :libev and :libevent, these two engines require installed libcouchbase2-libev and libcouchbase2-libevent packages correspondingly. Currently they aren't so friendly to GVL but still useful.

  • :eventmachine engine. From version 1.2.2 it is possible to use great EventMachine library as underlying IO backend and integrate couchbase gem to your current asynchronous application. This engine will be only accessible on the MRI ruby 1.9+. Checkout simple example of usage:

    require 'eventmachine'
    require 'couchbase'
    EM.epoll = true  if EM.epoll?
    EM.kqueue = true  if EM.kqueue? do
      con = Couchbase.connect :engine => :eventmachine, :async => true
      con.on_connect do |res|
        puts "connected: #{res.inspect}"
        if res.success?
          con.set("emfoo", "bar") do |res|
            puts "set: #{res.inspect}"
            con.get("emfoo") do |res|
              puts "get: #{res.inspect}"