learning_graph_database_gremlin_tinkerpop.md

path	title
/learnings/graph_databases	Learnings: Graph Databases

Table Of Contents

• Learning Graph Database : Gremlin / Tinkerpop >
  • Exploring a graph in Gremlin Console
    • See also
  • TinkerPop APIs
    • Graph Structure API (org.apache.tinkerpop.gremlin.structure.Graph) >
    • Traversal API (org.apachae.tinkerpop.gremlin.process.dsl.graph.GraphTraversal) >
    • and connecting to Gremlin Server
      • Remote connection example (JanusGraph)
  • Profiling
  • See also:
• Learning Graph Database: Gremlin-Scala >
  • and remote Gremlin Servers
  • See also:
• Learning Graph Databases: Gremlin Server >
  • Setting up for HTTP mode
  • Samples for HTTP mode
  • And HA concerns
  • And configurations that matter to the client
  • See also:
• Learning Graph Databases: Gremlin Console >

Learning Graph Database : Gremlin / Tinkerpop <<Learning_GraphDatabase_Gremlin_Tinkerpop>>

Exploring a graph in Gremlin Console

gremlin> g.V().has("name", "saturn")    // queries for verticies that have name "saturn"

gremlin> g.V().has("name", "saturn").outE()  // gets edge coming out

See also

• IBM CloudDocs creating / traversing a Graph using Gremlin console
• Gremlin Graph Guide PDF <--- TinkerPop, Gremlin, and Janus Graph!!!

TinkerPop APIs

Graph Structure API (org.apache.tinkerpop.gremlin.structure.Graph) <<Learning_GraphDatabase_Gremlin_Tinkerpop_APIS_Structure>>

Gremlin Guide, section 4.5.1:

It is strongly recommended that the traversal source object g be used when adding, NOTE updating or deleting vertices and edges. Using the graph object directly is not viewed as a TinkerPop best practice.

• source ????????

Traversal API (org.apachae.tinkerpop.gremlin.process.dsl.graph.GraphTraversal) <<Learning_GraphDatabase_Gremlin_Tinkerpop_APIS_Traversal>>

NOTE: Need to always call .next() or .iterate() to save data to the graph. Source

ALSO: https://tinkerpop.apache.org/docs/current/reference/#graph-traversal-steps

and connecting to Gremlin Server

1. MUST(??) use Websockets mode for server instead of HTTP mode for Gremlin / Tinkerpop communications

Tinkerpop when given address will create ws:// URL instead of http:// line

2. Can ONLY run Websocket Mode OR HTTP mode - can not run both Stackoverflow answer

3. Remote connections are done via (Remote) Traversal API

Remote connection example (JanusGraph)

val graph = JanusGraphFactory.open("inmemory")
val g : GraphTraversalSource = graph.traversal().withRemote( conf )

Q: Why not EmptyGraph(), like the examples say?

A: EmptyGraph doesn't seem to support transactions, add edges, etc etc. (???). See also stackoverflow answer on JanusGraphFactory inmemory ... because it doesn't have the JanusGraph goodness baked in (EmptyGraph is a Tinkerpop thing!)

Profiling

.profile <-- outputs time / traverse info about your traversal

See also:

• https://github.com/tinkerpop/gremlin/wiki/basic-graph-traversals

Learning Graph Database: Gremlin-Scala <<Learning_GraphDatabase_Gremlin_Scala>>

and remote Gremlin Servers

??? Need to be careful about what is and is not supported with gremlin server ie: + , -----, operators may not use the Traversal API (see: Learning_GraphDatabase_Gremlin_Tinkerpop_APIS_Traversal ) and may not support certain operations (????)

• My Github issue comment here

See also:

• Gremlin-Scala Examples

Learning Graph Databases: Gremlin Server <<Learning_GraphDatabases_Gremlin_Server>>

Can only use one mode: HTTP or WebSockets mode. Sources:

• Stackoverflow answer
• Answer to JIRA Ticket filed in TINKERPOP Project RE this topic

Setting up for HTTP mode

NOTE: configuration only valid for server. If you try to connect via Gremlin with this configuration it will barf (only partially related to URL schema of ws:// by Tinkerpop)

In config file set: channelizer: org.apache.tinkerpop.gremlin.server.channel.HttpChannelizer

NOTE: HTTP / "REST" mode is not really RESTful

Samples for HTTP mode

• Sample CURL statements / responses for HTTP/REST
• Connecting to JanusGraph with HTTP Requests

And HA concerns

• Stackoverflow answer for Gremlin Servers behind load balancers

• Health Check: http://myhostname:8182/?gremlin=100-1 <-- or ws://... ( Stackoverflow answer source )

  NOTE: in Websocket mode this connection, of course, never closes. In HTTP mode it does not keep alive.

And configurations that matter to the client

??? graphs: { } in gremlin-server.yml needs to have same graph name in it as the Gremlin clients are trying to connect to (need to share YAML file, or parts of YAML file somehow??????)

See also:

• And using gremlin servers: mpollmeier/gremlin-scala#223 (comment)

Learning Graph Databases: Gremlin Console <<Learning_GraphDatabase_Gremlin_Console>>

gremlin> graph = JanusGraphFactory.open('janusgraph.properties')
Backend shorthand unknown: janusgraph.properties

^^^^^ means that it can not find the properties file you are pointing at. Try using a relative path or just the full path in your string.