Quickstart

Neo4j Connector for Apache Spark allows you to read from and write to Neo4j databases.

It’s fairly easy to use, although it can be highly customized.

Installation guide

Where to get the JARs?

You can download the connector JAR from the Neo4j Connector Page or from the GitHub releases page.

Choose the version carefully since the wrong combination of Scala version and Spark version breaks your code. Check this page for more information about the proper JAR to use.

Using spark-submit, spark-shell, or pyspark

$SPARK_HOME/bin/spark-shell --jars neo4j-connector-apache-spark_2.12-4.0.1_for_spark_3.jar

The connector is also available from Spark Packages:

$SPARK_HOME/bin/spark-shell --packages org.neo4j:neo4j-connector-apache-spark_2.12:4.0.1_for_spark_3

Using sbt

If you use the sbt-spark-package plugin, in your build.sbt file add:

scala spDependencies += "org.neo4j/neo4j-connector-apache-spark_${scala.version}:4.0.1_for_spark_${spark.version}"

Otherwise:

libraryDependencies += "org.neo4j" % "neo4j-connector-apache-spark_${scala.version}" % "4.0.1_for_spark_${spark.version}"

Using Maven

pom.xml
<dependencies>
  <!-- list of dependencies -->
  <dependency>
    <groupId>org.neo4j</groupId>
    <artifactId>neo4j-connector-apache-spark_${scala.version}</artifactId>
    <version>4.0.1_for_spark_${spark.version}</version>
  </dependency>
</dependencies>

Using Gradle

dependencies{
    // list of dependencies
    compile "org.neo4j:neo4j-spark-connector:${connector.version}"
}

Using the connector on Databricks

You need to first get the proper JAR for the Databricks Runtime Version, here you can find where to download the JARs.

Go to your cluster page, select the Library tab and install a new library simply by uploading the JAR.

This is it!

Getting started

You can read your Neo4j database and have the data available as Spark DataFrame.

Read all the nodes with of label Person
import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()

val df = spark.read.format("org.neo4j.spark.DataSource")
  .option("url", "bolt://localhost:7687")
  .option("authentication.basic.username", "neo4j")
  .option("authentication.basic.password", "neo4j")
  .option("labels", "Person")
  .load()

Similarly, it is possible to write your own DataFrame to Neo4j:

Write the DataFrame to nodes of label Person
import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()
import spark.implicits._

val df = Seq(
  ("John Doe"),
  ("Jane Doe")
).toDF("name")

df.write.format("org.neo4j.spark.DataSource")
  .mode(SaveMode.ErrorIfExists)
  .option("url", "bolt://localhost:7687")
  .option("authentication.basic.username", "neo4j")
  .option("authentication.basic.password", "neo4j")
  .option("labels", ":Person")
  .save()

Visit the Reading and Writing sections for advanced usage.

General considerations

Before going into details, we need to address you to some preliminary considerations on data types, filters, and schema.

Complex data types

Spark doesn’t support all Neo4j data types (i.e., Point, Time, Duration). Such types are transformed into Struct types containing all the useful data.

For complete details on type handling, consult the Data type mapping between Neo4j and Spark.

Table 1. Complex data type conversion
Type Struct

Duration

 
Struct(Array(
    ("type", DataTypes.StringType, false),
    ("months", DataTypes.LongType, false),
    ("days", DataTypes.LongType, false),
    ("seconds", DataTypes.LongType, false),
    ("nanoseconds", DataTypes.IntegerType, false),
    ("value", DataTypes.StringType, false)
  ))

Point

 
Struct(Array(
    ("type", DataTypes.StringType, false),
    ("srid", DataTypes.IntegerType, false),
    ("x", DataTypes.DoubleType, false),
    ("y", DataTypes.DoubleType, false),
    ("z", DataTypes.DoubleType, true),
  ))

Time

 
Struct(Array(
    ("type", DataTypes.StringType, false),
    ("value", DataTypes.StringType, false)
  ))

Filters

The Neo4j Connector for Apache Spark implements the SupportPushdownFilters interface, that allows you to push the Spark filters down to the Neo4j layer. In this way the data that Spark receives have been already filtered by Neo4j, decreasing the amount of data transferred from Neo4j to Spark.

You can manually disable the PushdownFilters support using the pushdown.filters.enabled option and set it to false (default is true).

If you use the filter function more than once, like in this example:

import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()

val df = spark.read.format("org.neo4j.spark.DataSource")
  .option("url", "bolt://localhost:7687")
  .option("authentication.basic.username", "neo4j")
  .option("authentication.basic.password", "neo4j")
  .option("labels", ":Person")
  .load()

df.where("name = 'John Doe'").where("age = 32").show()

The conditions are automatically joined with an AND operator.

When using relationship.node.map = true or query the PushdownFilters support is automatically disabled, thus the filters are applied by Spark and not by Neo4j.

Aggregation

The Neo4j Connector for Apache Spark implements the SupportsPushDownAggregates interface, that allows you to push Spark aggregations down to the Neo4j layer. In this way the data that Spark receives have been already aggregate by Neo4j, decreasing the amount of data transferred from Neo4j to Spark.

You can manually disable the PushdownAggregate support using the pushdown.aggregate.enabled option and set it to false (default is true).

// Given a DB populated with the following query
"""CREATE (pe:Person {id: 1, fullName: 'Person'})
 |WITH pe
 |UNWIND range(1, 10) as id
 |CREATE (pr:Product {id: id * rand(), name: 'Product ' + id, price: id})
 |CREATE (pe)-[:BOUGHT{when: rand(), quantity: rand() * 1000}]->(pr)
 |RETURN *
"""
import org.apache.spark.sql.{SaveMode, SparkSession}
val spark = SparkSession.builder().getOrCreate()

spark.read.format("org.neo4j.spark.DataSource")
  .option("url", "bolt://localhost:7687")
  .option("relationship", "BOUGHT")
  .option("relationship.source.labels", "Person")
  .option("relationship.target.labels", "Product")
  .load
  .createTempView("BOUGHT")


val df = spark.sql(
  """SELECT `source.fullName`, MAX(`target.price`) AS max, MIN(`target.price`) AS min
    |FROM BOUGHT
    |GROUP BY `source.fullName`""".stripMargin)

df.show()

The MAX and MIN operators are applied directly on Neo4j.

Schema

Spark works with data in a fixed tabular schema. To accomplish this Neo4j Connector has a schema infer system that creates the schema based on the data retrieved from the database. Each read data method has its own strategy to create it, that is explained in the corresponding section.

In general, we first try to use APOC, if that is not available we flatten the first schema.flatten.limit results and try to infer the schema by the type of each column.

If you don’t want this process to happen, set schema.strategy to string (default is sample), and every column is presented as a string.

Schema strategy sample is good when all instances of a property in Neo4j are the same type, and string followed by cast is better when property types may differ. Remember that Neo4j does not enforce property typing, and so person.age could sometimes be a long and sometimes be a string.

Example

Using sample strategy
import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()

spark.read.format("org.neo4j.spark.DataSource")
  .option("url", "bolt://localhost:7687")
  .option("authentication.basic.username", "neo4j")
  .option("authentication.basic.password", "neo4j")
  .option("query", "MATCH (n:Person) WITH n LIMIT 2 RETURN id(n) as id, n.name as name")
  .load()
  .show()
Table 2. Result of the above code
id name

0

John Doe

1

Jane Doe
Using string strategy
import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()

spark.read.format("org.neo4j.spark.DataSource")
  .option("query", "MATCH (n:Person) WITH n LIMIT 2 RETURN id(n) as id, n.name as name")
  .option("schema.strategy", "string")
  .load()
  .show()
Table 3. Result of the above code
id name

"0"

"John Doe"

"1"

"Jane Doe"

As you can see, the Struct returned by the query is made of strings that you can then cast by using Spark’s getters (i.e., getLong).

User defined schema

You can skip the automatic schema extraction process by providing a user defined schema using the .schema() method.

Using user defined schema
import org.apache.spark.sql.types.{DataTypes, StructType, StructField}
import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()

spark.read.format("org.neo4j.spark.DataSource")
  .schema(StructType(StructField("id", DataTypes.StringType), StructField("name", DataTypes.StringType)))
  .option("query", "MATCH (n:Person) WITH n LIMIT 2 RETURN id(n) as id, n.name as name")
  .load()
  .show()
Table 4. Result of the above code
id name

"0"

"John Doe"

"1"

"Jane Doe"

In this way you have total control over the schema.

Known problem

Because Neo4j is a schema free database, the following scenario may occur:

CREATE (p1:Person {age: "32"}), (p2:Person {age: 23})

The same field on the same node label has two different types.

Spark doesn’t like it since the DataFrame requires a schema, meaning each column of the DataFrame needs to have its own type.

If you don’t have APOC installed on your Neo4j instance, you’re most likely to be exposed to errors like this:

java.lang.ClassCastException: org.apache.spark.unsafe.types.UTF8String cannot be cast to java.lang.Long

In this case you can either clean up and normalize your data, or install APOC.

APOC causes every value of attributes affected by this problem to be cast to String.

This solution is not error-proof, you might still get the errors. Behind the scenes the Connector uses apoc.meta.nodeTypeProperties and apoc.meta.relTypeProperties to sample the data.

When the casting operation happens, this warning appears in your log, letting you know what has happened:

The field "age" has different types: [String, Long]
Every value will be casted to string.

The safest solution is to clean your data, but that is not always possible. This is why schema.strategy is introduced, and you can set to string to get all the values converted to string.

Partitioning

While we’re trying to pull off the data we offer the possibility to partition the extraction in order parallelizing it.

Please consider the following job:

import org.apache.spark.sql.{SaveMode, SparkSession}

val spark = SparkSession.builder().getOrCreate()

val df = spark.read.format("org.neo4j.spark.DataSource")
        .option("url", "bolt://localhost:7687")
        .option("authentication.basic.username", "neo4j")
        .option("authentication.basic.password", "neo4j")
        .option("labels", "Person")
        .option("partitions", "5")
        .load()

This means that if the total count of the nodes with label Person into Neo4j is 100 we are creating 5 partitions and each one manages 20 records (we use SKIP / LIMIT queries).

Partitioning the dataset makes sense only if you’re dealing with a big dataset (>= 10M of records).

How to parallelize the query execution

Considering that you have three options:

  1. Node extraction.

  2. Relationship extraction.

  3. Query extraction.

A general count on what you’re trying to pull off is being provided and a query with SKIP / LIMIT approach over each partition is being built.

Therefore for a dataset of 100 nodes (Person) with a partition size of 5 the following queries are generated (one for partition):

MATCH (p:Person) RETURN p SKIP 0 LIMIT 20
MATCH (p:Person) RETURN p SKIP 20 LIMIT 20
MATCH (p:Person) RETURN p SKIP 40 LIMIT 20
MATCH (p:Person) RETURN p SKIP 60 LIMIT 20
MATCH (p:Person) RETURN p SKIP 80 LIMIT 20

While for (1) and (2) you leverage the Neo4j count store in order to retrieve the total count about the nodes/relationships you’re trying pulling off, for the (3) you have two possible approaches:

  • Compute a count over the query that you’re using.

  • Compute a count over a second optimized query that leverages indexes. In this case you can pass it via the .option("query.count", "<your cypher query>") the query must always return only one field named count which is the result of the count:

MATCH (p:Person)-[r:BOUGHT]->(pr:Product)
WHERE pr.name = 'An Awesome Product'
RETURN count(p) AS count

Examples

You can find examples on how to use the Neo4j Connector for Apache Spark at this repository. It’s a collection of Zeppelin Notebooks with different usage scenarios, along with a getting started guide.

The repository is in constant development, and feel free to submit your examples.