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Utility library providing mapping to virtual buckets

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README.markdown

libvbucket: a vbucket library for memcached

Config Syntax

libvbucket uses JSON for it's configuration format. The directory tests/config contains sample configurations for vbucket and ketama distribution algorithms taken from a live Couchbase cluster.

Envelope Section

Configurations can have an optional envelope. If it is absent, libvbucket will treat the config stream as a VBucket section.

name

The username which should be used for nodes. This will be used for both authentication in HTTP and over memcached binary protocol. Note that "default" is a special bucket which does not use HTTP auth or memcached protocol auth. Specifying "default" and empty string for password will configure the client to use the default bucket.

"name": "default",

saslPassword

The password which should be used for nodes, which need authentication.

"saslPassword": "",

nodeLocator

The distribution algorithm which will be used to map keys to nodes. If this field is absent the vbucket locator will be used. The possible values are ketama and vbucket.

"nodeLocator": "vbucket",

vBucketServerMap

The section which describes the vbucket configuration. See the "VBucket Section" below.

nodes

The list of objects which describe the nodes in the cluster. The parser will look for couchApiBase, hostname and ports fields in this entry.

  • hostname

    The hostname and port of the cluster's REST interface.

    "hostname": "172.16.16.76:8091",
    
  • couchApiBase

    The endpoint for CouchDB REST interface. This endpoint should be used for Couch view execution.

    "couchApiBase": "http://172.16.16.76:8091/default",
    
  • ports

    List of node ports. Currenty it contains direct and proxy port to connect to the node using memcached protocol. The proxy port could be used for vbucket unaware, legacy clients.

    "ports": {
      "proxy": 11211,
      "direct": 11210
    },
    

VBucket Section

The configuration string is JSON.

Example:

{
  "hashAlgorithm": "CRC",
  "numReplicas": 2,
  "serverList": ["server1:11211", "server2:11210", "server3:11211"],
  "vBucketMap":
    [
      [0, 1, 2],
      [1, 2, 0],
      [2, 1, -1],
      [1, 2, 0]
    ]
}

hashAlgorithm

The hash algorithm can be in upper or lower case. libvbucket currently uses a CRC32 hashing algorithm, a good general purpose hash for short strings. The hash algorithm will typically be ketama for memcached type buckets.

numReplicas

numReplicas is the number of extra copies that will be stored on servers. Each vBucket in vBucketMap must have this number of server indexes plus one (the master server).

serverList

This has one string per server, in whatever format your app expects a server config string in. This may change to be more structured later.

vBucketMap

This contains one entry per vBucket, and the number of entries must be a power of two. Each entry must be an array of numReplicas+1 zero-based indices into serverList, with the first entry indicating the master server for the bucket and the remaining entries specifying the replicas, in order. -1 indicates that no server is mapped for that particular master/replica of that particular vBucket.

Note there is also a vBucketMapForward which can be sent by the server in the case that changes are occurring. The vBucketMapForward indicates what the future state of the cluster layout will be.

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