使用Spark进行Cassandra数据加载的备忘录

这是一个简单的使用Spark进行Cassandra数据加载的备忘录。

请参考以下链接以获取 Cassandra 集群的构建步骤:
https://qiita.com/48hands/items/05c2ad0ea89fe13afd57

首先，创建Keyspace和Table。

$ ssh nosql1

[vagrant@nosql1 ~]$ cqlsh nosql1
Connected to develop-cluster at nosql1:9042.
[cqlsh 5.0.1 | Cassandra 3.11.2 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.

cqlsh> CREATE KEYSPACE test WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 2 };

cqlsh> CREATE TABLE test.kv(key text PRIMARY KEY, value int);

接下来，我们将使用Scala语言编写Spark代码。内容可以随意编写。

设置 build.sbt

name := "CassandraLoad"

version := "0.1"

scalaVersion := "2.11.12"

resolvers += "Spark Packages Repo" at "https://dl.bintray.com/spark-packages/maven"

libraryDependencies ++= Seq(
  "datastax" % "spark-cassandra-connector" % "2.0.1-s_2.11",
  "org.apache.spark" %% "spark-sql" % "2.2.0"
)

创建一个名为LoadSample.scala的文件

import org.apache.spark.rdd.RDD
import org.apache.spark.sql.{SaveMode, SparkSession}
import org.apache.spark.sql.cassandra._

object LoadSample {

  def main(args: Array[String]): Unit = {
    import spark.implicits._

    val dfs = for (i <- 1 to 100) yield {
      val rdd: RDD[Int] = spark.sparkContext.parallelize(1 to 100000)
      rdd.map(line => (s"key-$i-$line", line)).toDF("key", "value")
    }

    dfs.foreach(df =>
      df.write.cassandraFormat("kv", "test").mode(SaveMode.Overwrite).save())
  }


  private val spark = SparkSession
    .builder
    .master("local[*]") // ローカルでエグゼキュータにクライアントPCのコア数と同数のスレッドを割り当て
    .appName("Load Sample")
    .config("spark.cassandra.connection.host",
      "192.168.33.41,192.168.33.42,192.168.33.43")
    .config("spark.cassandra.output.consistency.level", "ONE") // デフォルトだとLOCAL_QUORUMなので変更した。
    .getOrCreate()
}

执行之后，数据应该包含100,000 * 100 = 10,000,000条记录。

$ ssh nosql1

[vagrant@nosql1 ~]$ cqlsh nosql1 -k test
Connected to develop-cluster at nosql1:9042.
[cqlsh 5.0.1 | Cassandra 3.11.2 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.

cqlsh:test> select * from kv limit 100;

 key         | value
-------------+---------
 key-4-28995 |   28995
 key-4-78904 |   78904
 key-4-61524 |   61524
 key-4-13764 |   13764
 ...

应该可以感觉到已经进入了。