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daewon [S2GRAPH-230] ResourceManager onEvict cause segmentation fault with A…

  [S2GRAPH-230] https://issues.apache.org/jira/browse/S2GRAPH-230

Pull Request:
  Closes #179

  DO YUNG YOON <steamshon@apache.org>
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S2Graph Build Status

S2Graph is a graph database designed to handle transactional graph processing at scale. Its REST API allows you to store, manage and query relational information using edge and vertex representations in a fully asynchronous and non-blocking manner.

S2Graph is a implementation of Apache TinkerPop on Apache HBASE.

This document covers some basic concepts and terms of S2Graph as well as help you get a feel for the S2Graph API.

Building from the source

To build S2Graph from the source, install the JDK 8 and SBT, and run the following command in the project root:

sbt package
This will create a distribution of S2Graph that is ready to be deployed.

One can find distribution on target/apache-s2graph-$version-incubating-bin.

Quick Start

Once extracted the downloaded binary release of S2Graph or built from the source as described above, the following files and directories should be found in the directory.

LICENCE               # the Apache License 2.0  
bin                   # scripts to manage the lifecycle of S2Graph  
conf                  # configuration files  
lib                   # contains the binary  
logs                  # application logs  
var                   # application data  

This directory layout contains all binary and scripts required to launch S2Graph. The directories logs and var may not be present initially, and are created once S2Graph is launched.

The following will launch S2Graph, using HBase in the standalone mode for data storage and H2 as the metadata storage.

sh bin/start-s2graph.sh
To connect to a remote HBase cluster or use MySQL as the metastore, refer to the instructions in conf/application.conf.
S2Graph is tested on HBase versions 0.98, 1.0, 1.1, and 1.2 (https://hub.docker.com/r/harisekhon/hbase/tags/).

Project Layout

Here is what you can find in each subproject.

  1. s2core: The core library, containing the data abstractions for graph entities, storage adapters and utilities.
  2. s2rest_play: The REST server built with Play framework, providing the write and query API.
  3. s2rest_netty: The REST server built directly using Netty, implementing only the query API.
  4. s2graphql: The GraphQL server, providing standard web interface for S2Graph.
    4. loader: A collection of Spark jobs for bulk loading streaming data into S2Graph.
    5. spark: Spark utilities for loader and s2counter_loader.
  5. s2jobs: A collection of Spark jobs to support OLAP on S2Graph.
  6. s2counter_core: The core library providing data structures and logics for s2counter_loader.
  7. s2counter_loader: Spark streaming jobs that consume Kafka WAL logs and calculate various top-K results on-the-fly.
  8. s2graph_gremlin: Gremlin plugin for tinkerpop users.

The first four projects are for OLTP-style workloads, currently the main target of S2Graph.
The remaining projects are for OLAP-style workloads, especially for integrating S2Graph with other projects, such as Apache Spark and Kafka.
The loader and spark projects are deprecated by s2jobs since version 0.2.0.

Note that, the OLAP-style workloads are under development and we are planning to provide documentations in the upcoming releases.

Your First Graph

Once the S2Graph server has been set up, you can now start to send HTTP queries to the server to create a graph and pour some data in it. This tutorial goes over a simple toy problem to get a sense of how S2Graph's API looks like. bin/example.sh contains the example code below.

The toy problem is to create a timeline feature for a simple social media, like a simplified version of Facebook's timeline😜. Using simple S2Graph queries it is possible to keep track of each user's friends and their posts.

  1. First, we need a name for the new service.

The following POST query will create a service named "KakaoFavorites".

curl -XPOST localhost:9000/graphs/createService -H 'Content-Type: Application/json' -d '
{"serviceName": "KakaoFavorites", "compressionAlgorithm" : "gz"}

To make sure the service is created correctly, check out the following.

curl -XGET localhost:9000/graphs/getService/KakaoFavorites
  1. Next, we will need some friends.

In S2Graph, relationships are organized as labels. Create a label called friends using the following createLabel API call:

curl -XPOST localhost:9000/graphs/createLabel -H 'Content-Type: Application/json' -d '
  "label": "friends",
  "srcServiceName": "KakaoFavorites",
  "srcColumnName": "userName",
  "srcColumnType": "string",
  "tgtServiceName": "KakaoFavorites",
  "tgtColumnName": "userName",
  "tgtColumnType": "string",
  "isDirected": "false",
  "indices": [],
  "props": [],
  "consistencyLevel": "strong"

Check if the label has been created correctly:+

curl -XGET localhost:9000/graphs/getLabel/friends

Now that the label friends is ready, we can store the friendship data. Entries of a label are called edges, and you can add edges with edges/insert API:

curl -XPOST localhost:9000/graphs/edges/insert -H 'Content-Type: Application/json' -d '
  {"from":"Elmo","to":"Big Bird","label":"friends","props":{},"timestamp":1444360152477},
  {"from":"Cookie Monster","to":"Grover","label":"friends","props":{},"timestamp":1444360152480},
  {"from":"Cookie Monster","to":"Kermit","label":"friends","props":{},"timestamp":1444360152481},
  {"from":"Cookie Monster","to":"Oscar","label":"friends","props":{},"timestamp":1444360152482}

Query friends of Elmo with getEdges API:

curl -XPOST localhost:9000/graphs/getEdges -H 'Content-Type: Application/json' -d '
  "srcVertices": [{"serviceName": "KakaoFavorites", "columnName": "userName", "id":"Elmo"}],
  "steps": [
    {"step": [{"label": "friends", "direction": "out", "offset": 0, "limit": 10}]}

Now query friends of Cookie Monster:

curl -XPOST localhost:9000/graphs/getEdges -H 'Content-Type: Application/json' -d '
  "srcVertices": [{"serviceName": "KakaoFavorites", "columnName": "userName", "id":"Cookie Monster"}],
  "steps": [
    {"step": [{"label": "friends", "direction": "out", "offset": 0, "limit": 10}]}
  1. Users of Kakao Favorites will be able to post URLs of their favorite websites.

We will need a new label post for this data:

curl -XPOST localhost:9000/graphs/createLabel -H 'Content-Type: Application/json' -d '
  "label": "post",
  "srcServiceName": "KakaoFavorites",
  "srcColumnName": "userName",
  "srcColumnType": "string",
  "tgtServiceName": "KakaoFavorites",
  "tgtColumnName": "url",
  "tgtColumnType": "string",
  "isDirected": "true",
  "indices": [],
  "props": [],
  "consistencyLevel": "strong"

Now, insert some posts of the users:

curl -XPOST localhost:9000/graphs/edges/insert -H 'Content-Type: Application/json' -d '
  {"from":"Big Bird","to":"www.kakaocorp.com/en/main","label":"post","props":{},"timestamp":1444360152477},
  {"from":"Big Bird","to":"github.com/kakao/s2graph","label":"post","props":{},"timestamp":1444360152478},

Query posts of Big Bird:

curl -XPOST localhost:9000/graphs/getEdges -H 'Content-Type: Application/json' -d '
  "srcVertices": [{"serviceName": "KakaoFavorites", "columnName": "userName", "id":"Big Bird"}],
  "steps": [
    {"step": [{"label": "post", "direction": "out", "offset": 0, "limit": 10}]}
  1. So far, we have designed a label schema for the labels friends and post, and stored some edges to them.+

This should be enough for creating the timeline feature! The following two-step query will return the URLs for Elmo's timeline, which are the posts of Elmo's friends:

curl -XPOST localhost:9000/graphs/getEdges -H 'Content-Type: Application/json' -d '
  "srcVertices": [{"serviceName": "KakaoFavorites", "columnName": "userName", "id":"Elmo"}],
  "steps": [
    {"step": [{"label": "friends", "direction": "out", "offset": 0, "limit": 10}]},
    {"step": [{"label": "post", "direction": "out", "offset": 0, "limit": 10}]}

Also try Cookie Monster's timeline:

curl -XPOST localhost:9000/graphs/getEdges -H 'Content-Type: Application/json' -d '
  "srcVertices": [{"serviceName": "KakaoFavorites", "columnName": "userName", "id":"Cookie Monster"}],
  "steps": [
    {"step": [{"label": "friends", "direction": "out", "offset": 0, "limit": 10}]},
    {"step": [{"label": "post", "direction": "out", "offset": 0, "limit": 10}]}

The example above is by no means a full blown social network timeline, but it gives you an idea of how to represent, store and query graph data with S2Graph.+

TinkerPop Support

Since version 0.2.0-incubating, S2Graph integrate natively with Apache TinkerPop 3.2.5. S2Graph passes Apache TinkerPop's StructureStandardSuite and ProcessStandardSuite test suites.

Graph Features not implemented.

  • Computer
  • Transactions
  • ThreadedTransactions

Vertex Features not implemented.

  • MultiProperties
  • MetaProperties
  • UuidIds
  • AnyIds
  • NumericIds
  • StringIds

Edge Features not implemented.

  • UuidIds
  • AnyIds
  • NumericIds
  • StringIds

Vertex property features not implemented.

  • UuidIds
  • AnyIds
  • NumericIds
  • StringIds
  • MapValues
  • MixedListValues
  • BooleanArrayValues
  • ByteArrayValues
  • DoubleArrayValues
  • FloatArrayValues
  • IntegerArrayValues
  • StringArrayValues
  • LongArrayValues
  • SerializableValues
  • UniformListValues

Edge property feature not implemented.

  • MapValues
  • MixedListValues
  • BooleanArrayValues
  • ByteArrayValues
  • DoubleArrayValues
  • FloatArrayValues
  • IntegerArrayValues
  • StringArrayValues
  • LongArrayValues
  • SerializableValues
  • UniformListValues

NOTE: This is an ongoing task.

Getting Started

Maven coordinates



S2Graph is a singleton that can be shared among multiple threads. You instantiate S2Graph using the standard TinkerPop static constructors.

  • Graph g = S2Graph.open(final Configuration configuration)

Some important properties for configuration.

HBase for data storage.


RDBMS for meta storage.


Gremlin Console

1. install plugin

On gremlin console, it is possible to install s2graph as follow.

:install org.apache.s2graph s2graph-gremlin 0.2.0
:plugin use tinkerpop.s2graph

Example run.

shonui-MacBook-Pro:apache-tinkerpop-gremlin-console-3.2.5 shon$ bin/gremlin.sh

         (o o)
plugin activated: tinkerpop.server
plugin activated: tinkerpop.utilities
plugin activated: tinkerpop.tinkergraph
gremlin> :install org.apache.s2graph s2graph-gremlin 0.2.0
==>Loaded: [org.apache.s2graph, s2graph-gremlin, 0.2.0] - restart the console to use [tinkerpop.s2graph]
gremlin> :plugin use tinkerpop.s2graph
==>tinkerpop.s2graph activated
gremlin> :plugin list

Once s2graph-gremlin plugin is acvive, then following example will generate tinkerpop's modern graph in s2graph.

Taken from TinkerPop

Modern Graph from Tinkerpop

tp3 modern graph(simple).

conf = new BaseConfiguration()
graph = S2Graph.open(conf)

// init system default schema

// init extra schema for tp3 modern graph.

// load modern graph into current graph instance.

// traversal
t = graph.traversal()

// show all vertices in this graph.

// show all edges in this graph.

// add two vertices.
shon = graph.addVertex(T.id, 10, T.label, "person", "name", "shon", "age", 35)
s2graph = graph.addVertex(T.id, 11, T.label, "software", "name", "s2graph", "lang", "scala")

// add one edge between two vertices.
created = shon.addEdge("created", s2graph, "_timestamp", 10, "weight", 0.1)

// check if new edge is available through traversal
t.V().has("name", "shon").out()

// shutdown

Note that simple version used default schema for Service, Column, Label for compatibility. Please checkout advanced example below to understand what data model is available on S2Graph.

tp3 modern graph(advanced).

It is possible to separate multiple namespaces into logical spaces. S2Graph achieve this by following data model. details can be found on https://steamshon.gitbooks.io/s2graph-book/content/the_data_model.html.

  1. Service: the top level abstraction

A convenient logical grouping of related entities Similar to the database abstraction that most relational databases support.

  1. Column: belongs to a service.

A set of homogeneous vertices such as users, news articles or tags. Every vertex has a user-provided unique ID that allows the efficient lookup. A service typically contains multiple columns.

  1. Label: schema for edge

A set of homogeneous edges such as friendships, views, or clicks. Relation between two columns as well as a recursive association within one column. The two columns connected with a label may not necessarily be in the same service, allowing us to store and query data that spans over multiple services.

Instead of convert user provided Id into internal unique numeric Id, S2Graph simply composite service and column metadata with user provided Id to guarantee global unique Id.

Following is simple example to exploit these data model in s2graph.

// init graph
graph = S2Graph.open(new BaseConfiguration())

// 0. import necessary methods for schema management.
import static org.apache.s2graph.core.Management.*

// 1. initialize dbsession for management which store schema into RDBMS.
session = graph.dbSession()

// 2. properties for new service "s2graph".

serviceName = "s2graph"
cluster = "localhost"
hTableName = "s2graph"
preSplitSize = 0
hTableTTL = -1
compressionAlgorithm = "gz"

// 3. actual creation of s2graph service.
// details can be found on https://steamshon.gitbooks.io/s2graph-book/content/create_a_service.html

service = graph.management.createService(serviceName, cluster, hTableName, preSplitSize, hTableTTL, compressionAlgorithm)

// 4. properties for user vertex schema belongs to s2graph service.

columnName = "user"
columnType = "integer"

// each property consist of (name: String, defaultValue: String, dataType: String)
// defailts can be found on https://steamshon.gitbooks.io/s2graph-book/content/create_a_servicecolumn.html
props = [newProp("name", "-", "string"), newProp("age", "-1", "integer")]

schemaVersion = "v3"
user = graph.management.createServiceColumn(serviceName, columnName, columnType, props, schemaVersion)

// 2.1 (optional) global vertex index.
graph.management.buildGlobalVertexIndex("global_vertex_index", ["name", "age"])

// 3. create VertexId
// create S2Graph's VertexId class.
v1Id = graph.newVertexId(serviceName, columnName, 20)
v2Id = graph.newVertexId(serviceName, columnName, 30)

shon = graph.addVertex(T.id, v1Id, "name", "shon", "age", 35)
dun = graph.addVertex(T.id, v2Id, "name", "dun", "age", 36)

// 4. friends label
labelName = "friend_"
srcColumn = user
tgtColumn = user
isDirected = true
indices = []
props = [newProp("since", "-", "string")]
consistencyLevel = "strong"
hTableName = "s2graph"
hTableTTL = -1
options = null

friend = graph.management.createLabel(labelName, srcColumn, tgtColumn,
        isDirected, serviceName, indices, props, consistencyLevel,
        hTableName, hTableTTL, schemaVersion, compressionAlgorithm, options)

shon.addEdge(labelName, dun, "since", "2017-01-01")

t = graph.traversal()

println "All Edges"
println t.E().toList()

println "All Vertices"
println t.V().toList()

println "Specific Edge"
println t.V().has("name", "shon").out().toList()


physical data storage is closed related to data model(https://steamshon.gitbooks.io/s2graph-book/content/the_data_model.html).

in HBase storage, Vertex is stored in v column family, and Edge is stored in e column family.

each Service/Label can have it's own dedicated HBase Table.

How Edge/Vertex is actually stored in KeyValue in HBase is described in details.


will be updated.


will be updated.


S2Graph has full support for gremlin. However gremlin’s fine grained graphy nature results in very high latency

Provider suppose to provide ProviderOptimization to improve latency of traversal, and followings are currently available optimizations.

NOTE: This is an ongoing task

1. S2GraphStep

  1. translate multiple has step into lucene query and find out vertexId/edgeId can be found from index provider, lucene.
  2. if vertexId/edgeId can be found, then change full scan into point lookup using list of vertexId/edgeId.

for examples, following traversal need full scan on storage if there is no index provider.

g.V().has("name", "steamshon").out()
g.V().has("name", "steamshon").has("age", P.eq(30).or(P.between(20, 30)))

once following global vertex index is created, then S2GraphStep translate above traversal into lucene query, then get list of vertexId/edgeId which switch full scan to points lookup.

graph.management.buildGlobalVertexIndex("global_vertex_index", ["name", "age"])

The Official Website

S2Graph API document

Mailing Lists