Import data from ClickHouse

This topic provides an example of how to use Exchange to import data stored on ClickHouse into NebulaGraph.

Data set

This topic takes the basketballplayer dataset as an example.

Environment

This example is done on MacOS. Here is the environment configuration information:

• Hardware specifications:
  • CPU: 1.7 GHz Quad-Core Intel Core i7
  • Memory: 16 GB

• Spark: 2.4.7, stand-alone

• Hadoop: 2.9.2, pseudo-distributed deployment

• ClickHouse: docker deployment yandex/clickhouse-server tag: latest(2021.07.01)

• NebulaGraph: 3.2.1. Deploy NebulaGraph with Docker Compose.

Prerequisites

Before importing data, you need to confirm the following information:

• NebulaGraph has been installed and deployed with the following information:

  • IP addresses and ports of Graph and Meta services.
  • The user name and password with write permission to NebulaGraph.

• Exchange has been compiled, or download the compiled .jar file directly.

• Spark has been installed.

• Learn about the Schema created in NebulaGraph, including names and properties of Tags and Edge types, and more.

• The Hadoop service has been installed and started.

Steps

Step 1: Create the Schema in NebulaGraph

Analyze the data to create a Schema in NebulaGraph by following these steps:

1. Identify the Schema elements. The Schema elements in the NebulaGraph are shown in the following table.

   Element	Name	Property
   Tag	player	name string, age int
   Tag	team	name string
   Edge Type	follow	degree int
   Edge Type	serve	start_year int, end_year int

2. Create a graph space basketballplayer in the NebulaGraph and create a Schema as shown below.

   ## Create a graph space.
   nebula> CREATE SPACE basketballplayer \
           (partition_num = 10, \
           replica_factor = 1, \
           vid_type = FIXED_STRING(30));
   
   ## Use the graph space basketballplayer.
   nebula> USE basketballplayer;
   
   ## Create the Tag player.
   nebula> CREATE TAG player(name string, age int);
   
   ## Create the Tag team.
   nebula> CREATE TAG team(name string);
   
   ## Create the Edge type follow.
   nebula> CREATE EDGE follow(degree int);
   
   ## Create the Edge type serve.
   nebula> CREATE EDGE serve(start_year int, end_year int);
   

For more information, see Quick start workflow.

Step 2: Modify configuration files

After Exchange is compiled, copy the conf file target/classes/application.conf to set ClickHouse data source configuration. In this example, the copied file is called clickhouse_application.conf. For details on each configuration item, see Parameters in the configuration file.

{
  # Spark configuration
  spark: {
    app: {
      name: Nebula Exchange 3.0.0
    }
    driver: {
      cores: 1
      maxResultSize: 1G
    }
    cores: {
      max: 16
    }
  }

# NebulaGraph configuration
  nebula: {
    address:{
      # Specify the IP addresses and ports for Graph and Meta services.
      # If there are multiple addresses, the format is "ip1:port","ip2:port","ip3:port".
      # Addresses are separated by commas.
      graph:["127.0.0.1:9669"]
      meta:["127.0.0.1:9559"]
    }
    # The account entered must have write permission for the NebulaGraph space.
    user: root
    pswd: nebula
    # Fill in the name of the graph space you want to write data to in the NebulaGraph.
    space: basketballplayer
    connection: {
      timeout: 3000
      retry: 3
    }
    execution: {
      retry: 3
    }
    error: {
      max: 32
      output: /tmp/errors
    }
    rate: {
      limit: 1024
      timeout: 1000
    }
  }
  # Processing vertexes
  tags: [
    # Set the information about the Tag player.
    {
      name: player
      type: {
        # Specify the data source file format to ClickHouse.
        source: clickhouse
        # Specify how to import the data of vertexes into NebulaGraph: Client or SST.
        sink: client
      }

      # JDBC URL of ClickHouse
      url:"jdbc:clickhouse://192.168.*.*:8123/basketballplayer"

      user:"user"
      password:"123456"

      # The number of ClickHouse partitions
      numPartition:"5"

      sentence:"select * from player"

      # Specify the column names in the player table in fields, and their corresponding values are specified as properties in the NebulaGraph.
      # The sequence of fields and nebula.fields must correspond to each other.
      # If multiple column names need to be specified, separate them by commas.
      fields: [name,age]
      nebula.fields: [name,age]

      # Specify a column of data in the table as the source of vertex VID in the NebulaGraph.
      vertex: {
        field:playerid
        # policy:hash
      }

      # The number of data written to NebulaGraph in a single batch.
      batch: 256

      # The number of Spark partitions.
      partition: 32
    }

    # Set the information about the Tag Team.
    {
      name: team
      type: {
        source: clickhouse
        sink: client
      }
      url:"jdbc:clickhouse://192.168.*.*:8123/basketballplayer"
      user:"user"
      password:"123456"
      numPartition:"5"
      sentence:"select * from team"
      fields: [name]
      nebula.fields: [name]
      vertex: {
        field:teamid
      }
      batch: 256
      partition: 32
    }
  ]

  # Processing edges
  edges: [
    # Set the information about the Edge Type follow.
    {
      # The corresponding Edge Type name in NebulaGraph.
      name: follow

      type: {
        # Specify the data source file format to ClickHouse.
        source: clickhouse

        # Specify how to import the data into NebulaGraph: Client or SST.
        sink: client
      }

      # JDBC URL of ClickHouse
      url:"jdbc:clickhouse://192.168.*.*:8123/basketballplayer"

      user:"user"
      password:"123456"

      # The number of ClickHouse partitions.
      numPartition:"5"

      sentence:"select * from follow"

      # Specify the column names in the follow table in fields, and their corresponding values are specified as properties in the NebulaGraph.
      # The sequence of fields and nebula.fields must correspond to each other.
      # If multiple column names need to be specified, separate them by commas.
      fields: [degree]
      nebula.fields: [degree]

      # In source, use a column in the follow table as the source of the edge's source vertexes.
      source: {
        field:src_player
      }

      # In target, use a column in the follow table as the source of the edge's destination vertexes.
      target: {
        field:dst_player
      }

      # (Optional) Specify a column as the source of the rank.
      #ranking: rank

      # The number of data written to NebulaGraph in a single batch.
      batch: 256

      # The number of Spark partitions.
      partition: 32
    }

    # Set the information about the Edge Type serve.
    {
      name: serve
      type: {
        source: clickhouse
        sink: client
      }
      url:"jdbc:clickhouse://192.168.*.*:8123/basketballplayer"
      user:"user"
      password:"123456"
      numPartition:"5"
      sentence:"select * from serve"
      fields: [start_year,end_year]
      nebula.fields: [start_year,end_year]
      source: {
        field:playerid
      }
      target: {
        field:teamid
      }

      # (Optional) Specify a column as the source of the rank.
      #ranking: rank

      batch: 256
      partition: 32
    }
  ]
}

Step 3: Import data into NebulaGraph

Run the following command to import ClickHouse data into NebulaGraph. For descriptions of the parameters, see Options for import.

${SPARK_HOME}/bin/spark-submit --master "local" --class com.vesoft.nebula.exchange.Exchange <nebula-exchange-3.0.0.jar_path> -c <clickhouse_application.conf_path>

Note

JAR packages are available in two ways: compiled them yourself, or download the compiled .jar file directly.

For example:

${SPARK_HOME}/bin/spark-submit  --master "local" --class com.vesoft.nebula.exchange.Exchange  /root/nebula-exchange/nebula-exchange/target/nebula-exchange-3.0.0.jar  -c /root/nebula-exchange/nebula-exchange/target/classes/clickhouse_application.conf

You can search for batchSuccess.<tag_name/edge_name> in the command output to check the number of successes. For example, batchSuccess.follow: 300.

Step 4: (optional) Validate data

Users can verify that data has been imported by executing a query in the NebulaGraph client (for example, NebulaGraph Studio). For example:

GO FROM "player100" OVER follow;

Users can also run the SHOW STATS command to view statistics.

Step 5: (optional) Rebuild indexes in NebulaGraph

With the data imported, users can recreate and rebuild indexes in NebulaGraph. For details, see Index overview.

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Last update: February 1, 2023