ClusterDicts

Global and Distributed dictionaries for Julia.

GlobalDict and DistributedDict

This package provides two types of distributed dictionaries:

• GlobalDict where the same key-value pair is stored on all participating workers.
• DistributedDict where the key-value pairs are distributed over the participating workers based on the key's hash value.

Constructors

• GlobalDict(pids=PidsWorkers(); name::AbstractString=next_name(), ktype=Any, vtype=Any) where

  • pids is one of PidsAll(), PidsWorkers() or Pids([ids...]) where

    • PidsAll() represents all processes in the cluster
    • PidsWorkers() represents all worker processes in the cluster
    • Pids([ids...]) represents a specific subset of workers identified by their pids.

  • name is a logical name for the dictionary. It should be unique across any such dictionary created across modules or different packages. Usually left unspecified in which case the system creates a unique name.

  • ktype is the type of the keys. Defaults to Any.

  • vtype is the type of the values. Defaults to Any.

• DistributedDict(pids=PidsWorkers(); name::AbstractString=next_name(), ktype=Any, vtype=Any) similar to the GlobalDict constructor.

• GlobalDict() and DistributedDict() only distribute over worker processes, i.e., excluding the master. Keyword args remain the same.

• GlobalDict(pids::Array) and DistributedDict(pids::Array) distribute on the specified pids. Keyword args remain the same.

Functions

The following functions of Associative are implemented:

• isempty
• length
• get
• get!
• getindex
• setindex!
• pop!
• delete!

ValueF

Any closure wrapped in a ValueF will execute the closure on the node where the key is being assigned.

For example, for a GlobalDict,

    d[k] = ValueF(()->myid())

will set the value of d[k] to 2 on pid 2, 3 on pid 3 and so on.

And for a DistributedDict, it will be set only on the node that the key hashes to.

Garbage Collection

The global and distributed dictionaries created by GlobalDict and DistributedDict are NOT collected when the objects go out of scope. They have to be necessarily released by calling delete!(d::GlobalDict) and delete!(d::DistributedDict) respectively.

TODO

• Concurrent updates : This current version makes no attempt to handle race conditions when multiple tasks or processes update the same key. For example, if d is a GlobalDict, d[k] = v sets k to v on all participating workers. If two tasks try to set d[k] = v1 and ``d[k] = v2at the same time, there is no guarantee the value will be either allv1` or all `v2` on all workers.

• More Associative functions to be implemented.

• Handle worker exits : Resiliency in the event of workers exiting has to be handled.