Supported Graph Databases

The Tinkerpop suite supports a number of graph data stores. They are all compatible with Pacer, but I have not yet implemented the simple adapters Pacer needs to use them yet. Here is the list of what's supported so far:

Graph	Info	Gem Required	Gem address
TinkerGraph	In-memory graph db. Included with Pacer.
OrientDB	A powerful and feature rich graph / document hybrid database.	gem install --pre pacer-orient	pangloss/pacer-orient
Neo4J	The industry-leading graph db.	gem install pacer-neo4j	pangloss/pacer-neo4j
Dex	A very fast, relatively new graph db.	gem install pacer-dex	pangloss/pacer-dex
Titan	Built on top of a pluggable nosql backend store	gem install pacer-titan	pacer-titan

You can run any or all of the above graph databases. Pacer supports running them simultaneously and even supports having many of any given type open at once.

TinkerGraph

Out of the box, Pacer comes with only the simple in-memory TinkerGraph, an excellent graph for testing and for temporary in-memory data. Start a TinkerGraph with:

tinkergraph = Pacer.tg

Neo4j

Neo4j is the primary database used by XN Logic, the team behind Pacer. It's an excellent, reliable and performant graph database that works well for a variety of use cases, and scales to easily support the largest data sets our customers have hit us with. Once the pacer-neo4j gem is installed, you can start a Neo graph with:

require 'pacer-neo4j'
neograph = Pacer.neo4j '/path/to/graph_dir'

As of August 2014, Pacer supports Neo4j v1.9 and v2.0. v2.1 support is in development.

(optional) Inter-operation with the neo4j gem

Pacer can work together with other Ruby GraphDB libraries, too. The first functioning example is with theo neo4j gem. Hopefully more will follow soon as I find out about them or get requests to support them.

To use Pacer together with the neo4j gem, get your Pacer graph instance as follows:

    require 'neo4j'
    require 'pacer-neo4j'
    # start neo4j via the external gem rather than using pacer-neo4j
    Neo4j.db.start
    graph = Pacer.neo4j(Neo4j.db.graph)

After that, you can continue to use the graph as normal with both gems. Any update that's committed with one gem will be visible immediately to the other because they are now both pointing to the same Java graphdb instance.

Titan

Pacer has Titan support via the pacer-titan community contributed gem. Titan is a distributed graph database focussed on supporting extremely large graphs. Once you've configured your project as required by the pacer-titan library, you can start a Titan graph like this:

require 'pacer-titan'
titangraph = Pacer.titan 'path/to/titan_config.properties'

Other graphs

Pacer can support OrientDB and Sparksee (formerly known as Dex) graph databases in addition to RDF graphs and others that I may not be aware of. The only requirement is that the graph have a Blueprints adapter. The pacer-neo4j and pacer-titan gems add graph-specific functionality on top of Pacer's built-in capabilities, but any blueprints compatibile graph can easily be used with Pacer with minimal effort.

A note on safely exiting

Some databases need to be shutdown cleanly when the program exits. You can shut a database down anytime by calling graph.shutdown, but you don't need to worry about it much. Pacer uses Ruby's at_exit hook to automatically shut down all open databases!