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Documentation

Saving RDDs to Cassandra

It is possible to save any RDD to Cassandra, not just a CassandraRDD. The only requirement is that the object class of RDD is a tuple or has property names corresponding to Cassandra column names.

It is possible to save an RDD to an existing Cassandra table as well as to let the connector create appropriate table automatically based on the definition of the RDD item class.

To save an RDD to an existing table, import com.datastax.spark.connector._ and call the saveToCassandra method with the keyspace name, table name and a list of columns. Make sure to include at least all primary key columns. To save an RDD to a new table, instead of calling saveToCassandra, call saveAsCassandraTable or saveAsCassandraTableEx.

Saving an RDD of Tuples

Example Saving an RDD of Tuples with Default Mapping

Assume the following table definition:

CREATE TABLE test.words (word text PRIMARY KEY, count int);
val collection = sc.parallelize(Seq(("cat", 30), ("fox", 40)))
collection.saveToCassandra("test", "words", SomeColumns("word", "count"))
cqlsh:test> select * from words;

 word | count
------+-------
  bar |    20
  foo |    10
  cat |    30
  fox |    40

(4 rows)

By default, Tuple fields will be paired in order with Cassandra Columns but using a custom mapper is also supported with tuples

Example Saving an RDD of Tuples with Custom Mapping

CREATE TABLE test.words (word text PRIMARY KEY, count int);
val collection = sc.parallelize(Seq((30, "cat"), (40, "fox")))
collection.saveToCassandra("test", "words", SomeColumns("word" as "_2", "count" as "_1"))
cqlsh:test> select * from words;

 word | count
------+-------
  cat |    30
  fox |    40

(2 rows)

Saving a collection of Scala Objects

When saving a collection of objects of a user-defined class, the items to be saved must provide appropriately named public property accessors for getting every column to be saved. This example provides more information on property-column naming conventions as described here.

Example Saving an RDD of Scala Objects

case class WordCount(word: String, count: Long)
val collection = sc.parallelize(Seq(WordCount("dog", 50), WordCount("cow", 60)))
collection.saveToCassandra("test", "words", SomeColumns("word", "count"))
cqlsh:test> select * from words;

 word | count
------+-------
  bar |    20
  foo |    10
  cat |    30
  fox |    40
  dog |    50
  cow |    60

The driver will execute a CQL INSERT statement for every object in the RDD, grouped in unlogged batches. The default consistency level for writes is LOCAL_QUORUM.

It is possible to specify custom column to property mapping with SomeColumns. If the property names in objects to be saved do not correspond to the column names in the destination table, use the as method on the column names you want to override. The parameter order is table column name first, then object property name.

Example Saving an RDD of Scala Objects with Custom Mapping

Say you want to save WordCount objects to the table which has columns word TEXT and num INT.

case class WordCount(word: String, count: Long)
val collection = sc.parallelize(Seq(WordCount("dog", 50), WordCount("cow", 60)))
collection.saveToCassandra("test", "words2", SomeColumns("word", "num" as "count"))

Modifying CQL Collections

The default behavior of the Spark Cassandra Connector is to overwrite collections when inserted into a cassandra table. To override this behavior you can specify a custom mapper with instructions on how you would like the collection to be treated.

The following operations are supported

  • append/add (lists, sets, maps)
  • prepend (lists)
  • remove (lists, sets)
  • overwrite (lists, sets, maps) :: Default

Remove is not supported for Maps.

These are applied by adding the desired behavior to the ColumnSelector

Example Column Selector using Custom Collection Behaviors

("key", "a_set" as "rddSetField" remove , "a_map" as "rddMapField" append)

This mapping takes the elements from rddSetField and removes them from corrosponding Cassandra Set "a_set". It also takes elements from "rddMapField" and adds them to the cassandra map "a_map" where the Cassandra column key quals the key field in the RDD elements.

Example Appending/Prepending To Cassandra Lists

CREATE TABLE ks.collections_mod (
      key int PRIMARY KEY,
      lcol list<text>,
      mcol map<text, text>,
      scol set<text>
  )
val listElements = sc.parallelize(Seq(
  (1,Vector("One")),
  (1,Vector("Two")),
  (1,Vector("Three"))))

val prependElements = sc.parallelize(Seq(
  (1,Vector("PrependOne")),
  (1,Vector("PrependTwo")),
  (1,Vector("PrependThree"))))

listElements.saveToCassandra("ks", "collections_mod", SomeColumns("key", "lcol" append))
prependElements.saveToCassandra("ks", "collections_mod", SomeColumns("key", "lcol" prepend))
cqlsh> Select * from ks.collections_mod where key = 1
   ... ;

 key | lcol                                                                | mcol | scol
-----+---------------------------------------------------------------------+------+------
   1 | ['PrependThree', 'PrependTwo', 'PrependOne', 'One', 'Two', 'Three'] | null | null

(1 rows)

Saving objects of Cassandra User Defined Types

To save structures consisting of many fields, use a Case Class or a com.datastax.spark.connector.UDTValue class. An instance of this class can be easily obtained from a Scala Map by calling fromMap factory method.

Assume the following table definition:

CREATE TYPE test.address (city text, street text, number int);
CREATE TABLE test.companies (name text PRIMARY KEY, address FROZEN<address>);

Example Using Case Classes to Insert into a Cassandra Row With UDTs

case class Address(street: String, city: String, zip: Int)
val address = Address(city = "Oakland", zip = 90210, street = "Broadway")
val col = Seq((1, "Joe", address))
sc.parallelize(col).saveToCassandra(ks, "udts", SomeColumns("key", "name", "addr"))

Example Using UDTValue.fromMap to Insert into a Cassandra Row With UDTs

import com.datastax.spark.connector.UDTValue
case class Company(name: String, address: UDTValue)
val address = UDTValue.fromMap(Map("city" -> "Santa Clara", "street" -> "Freedom Circle", "number" -> 3975))
val company = Company("DataStax", address)
sc.parallelize(Seq(company)).saveToCassandra("test", "companies")

Skipping Columns and Avoiding Tombstones on Writes (Connector Version 1.6+ and Cassandra 2.2+)

Prior to Cassandra 2.2 there was no way to execute a prepared statement with unbound elements. This meant every executed statement via the Spark Cassandra Connector was required to bind nulls into for any unspecified columns. As of Cassandra 2.2, the native protocol now allows for leaving parameters unbound.

To take advantage of unset parameters, the Spark Cassandra Connector now provides a method for taking advantage of this unbound behavior. This is done by with the com.datastax.spark.connector.types.CassandraOption trait.

The trait has three implementations

sealed trait CassandraOption[+A] extends Product with Serializable
  
  object CassandraOption {
    case class Value[+A](value: A) extends CassandraOption[A]
    case object Unset extends CassandraOption[Nothing]
    case object Null extends CassandraOption[Nothing]

This can be used when reading and writing from C*. When a column is loaded as a CassandraOption any missing columns will be represented as Unset. On writing, these parameters will remain unbound. This means a table loaded via CassandraOption can be written to a second table without any missing column values being treated as deletes.

Example Copying a table without deletes

//cqlsh
CREATE TABLE doc_example.tab1 (key INT, col_1 INT, col_2 INT, PRIMARY KEY (key))
INSERT INTO doc_example.tab1 (key, col_1, col_2) VALUES (1, null, 1)
CREATE TABLE doc_example.tab2 (key INT, col_1 INT, col_2 INT, PRIMARY KEY (key))
INSERT INTO doc_example.tab2 (key, col_1, col_2) VALUES (1, 5, null)
//spark-shell
val ks = "doc_example"
//Copy the data from tab1 to tab2 but don't delete when we see a null in tab1
sc.cassandraTable[(Int, CassandraOption[Int], CassandraOption[Int])](ks, "tab1")
  .saveToCassandra(ks, "tab2")
  
sc.cassandraTable[(Int,Int,Int)](ks, "tab2").collect
//(1, 5, 1)

For more complicated use cases the CassandraOption can be set to delete on a per row (and per column) basis. This is done by using either the Unset or Null case objects.

Example of using different None behaviors

//Fill tab1 with (1, 1, 1) , (2, 2, 2) ... (6, 6, 6)
sc.parallelize(1 to 6).map(x => (x, x, x)).saveToCassandra(ks, "tab1")
//Delete the second column when x >= 5
//Delete the third column when x <= 2
//For other rows put in the value -1
sc.parallelize(1 to 6).map(x => x match {
  case x if (x >= 5) => (x, CassandraOption.Null, CassandraOption.Unset)
  case x if (x <= 2) => (x, CassandraOption.Unset, CassandraOption.Null)
  case x => (x, CassandraOption(-1), CassandraOption(-1))
}).saveToCassandra(ks, "tab1")

val results = sc.cassandraTable[(Int, Option[Int], Option[Int])](ks, "tab1").collect
results 
/*
  (1, Some(1), None),
  (2, Some(2), None),
  (3, Some(-1), Some(-1)),
  (4, Some(-1), Some(-1)),
  (5, None, Some(5)),
  (6, None, Some(6)))
*/

CassandraOptions can be converted to Scala Options via an implemented implicit. This means that CassandraOptions can be dealt with as if they were normal Scala Options. For the reverse transformation, from a Scala Option into a CassandraOption, you need to define the None behavior. This is done via CassandraOption.deleteIfNone and CassandraOption.unsetIfNone

Example of converting Scala Options to Cassandra Options

import com.datastax.spark.connector.types.CassandraOption
//Setup original data (1, 1, 1) ... (6, 6, 6)
sc.parallelize(1 to 6).map(x => (x,x,x)).saveToCassandra(ks, "tab1")

//Setup options Rdd (1, None, None) (2, None, None) ... (6, None, None)
val optRdd = sc.parallelize(1 to 6)
  .map(x => (x, None, None))
   
//Delete the second column, but ignore the third column
optRdd
  .map{ case (x: Int, y: Option[Int], z: Option[Int]) =>
    (x, CassandraOption.deleteIfNone(y), CassandraOption.unsetIfNone(z))
  }.saveToCassandra(ks, "tab1")

val results = sc.cassandraTable[(Int, Option[Int], Option[Int])](ks, "tab1").collect
results
/*
    (1, None, Some(1)),
    (2, None, Some(2)),
    (3, None, Some(3)),
    (4, None, Some(4)),
    (5, None, Some(5)),
    (6, None, Some(6))
*/

Globally treating all nulls as Unset

WriteConf also now contains a parameter ignoreNulls which can be set via using a SparkConf key spark.cassandra.output.ignoreNulls. The default is false which will cause nulls to be treated as in previous versions (being inserted into C* as is). When set to true all nulls will be treated as unset. This can be used with DataFrames to skip null records and avoid tombstones.

####Example of using ignoreNulls to treat all nulls as Unset

//Setup original data (1, 1, 1) --> (6, 6, 6)
sc.parallelize(1 to 6).map(x => (x, x, x)).saveToCassandra(ks, "tab1")

val ignoreNullsWriteConf = WriteConf.fromSparkConf(sc.getConf).copy(ignoreNulls = true)
//These writes will not delete because we are ignoring nulls
val optRdd = sc.parallelize(1 to 6)
  .map(x => (x, None, None))
  .saveToCassandra(ks, "tab1", writeConf = ignoreNullsWriteConf)

val results = sc.cassandraTable[(Int, Int, Int)](ks, "tab1").collect

results
/**
  (1, 1, 1),
  (2, 2, 2),
  (3, 3, 3),
  (4, 4, 4),
  (5, 5, 5),
  (6, 6, 6)
**/

Specifying TTL and WRITETIME

By default Spark Cassandra Connector saves the data without explicitly specifying TTL or WRITETIME. But for users who require more flexibility, there are several options for setting WRITETIME and TTL

TTL and WRITETIME options are specified as properties of WriteConf object, which can be optionally passed to saveToCassandra method. TTL and WRITETIME options are specified independently from one another.

Using a constant value for all rows

When the same value should be used for all the rows, one can use the following syntax:

Example Setting a Single Value as the TTL of All Rows

import com.datastax.spark.connector.writer._
...
rdd.saveToCassandra("test", "tab", writeConf = WriteConf(ttl = TTLOption.constant(100)))
rdd.saveToCassandra("test", "tab", writeConf = WriteConf(timestamp = TimestampOption.constant(ts)))

TTLOption.constant accepts one of the following values:

  • Int / the number of seconds
  • scala.concurrent.duration.Duration
  • org.joda.time.Duration

TimestampOption.constant accepts one of the following values:

  • Long / the number of microseconds
  • java.util.Date
  • org.joda.time.DateTime

Using a different value for each row

When a different value of TTL or WRITETIME has to be used for each row, one can use the following syntax:

Example Setting the TTL Value based on the value of an RDD Column

import com.datastax.spark.connector.writer._
...
rdd.saveToCassandra("test", "tab", writeConf = WriteConf(ttl = TTLOption.perRow("ttl")))
rdd.saveToCassandra("test", "tab", writeConf = WriteConf(timestamp = TimestampOption.perRow("timestamp")))

perRow(String) method accepts a name of a property in each RDD item, which value will be used as TTL or WRITETIME value for the row.

Say we have an RDD with KeyValueWithTTL objects, defined as follows:

case class KeyValueWithTTL(key: Int, group: Long, value: String, ttl: Int)

val rdd = sc.makeRDD(Seq(
  KeyValueWithTTL(1, 1L, "value1", 100), 
  KeyValueWithTTL(2, 2L, "value2", 200), 
  KeyValueWithTTL(3, 3L, "value3", 300)))

and a CQL table:

CREATE TABLE IF NOT EXISTS test.tab (
    key INT, 
    group BIGINT, 
    value TEXT, 
    PRIMARY KEY (key, group)
)

When we run the following command:

import com.datastax.spark.connector.writer._
...
rdd.saveToCassandra("test", "tab", writeConf = WriteConf(ttl = TTLOption.perRow("ttl")))

the TTL for the 1st row will be 100, TTL for the 2nd row will be 200 and TTL for the 3rd row will be 300.

Saving rows only if they does not already exist

Spark Cassandra Connector always writes or updates data without checking if they already exist. It is possible to change this behaviour in exchange for performance penalty by the API.

IF NOT EXISTS can be added as a boolean property of WriteConf object, which can be optionally passed to saveToCassandra method:

Example using Cassandra Check and Set (CAS) to only write Rows if they do not already exist

import com.datastax.spark.connector.writer._
...
rdd.saveToCassandra("test", "tab", writeConf = WriteConf(ifNotExists = true))

Saving RDDs as new tables

Use saveAsCassandraTable method to automatically create a new table with given name and save the RDD into it. The keyspace you're saving to must exist. The following code will create a new table words_new in keyspace test with columns word and count, where word becomes a primary key:

Example Creating a New Table and Saving an RDD to it at the Same Time

case class WordCount(word: String, count: Long)
val collection = sc.parallelize(Seq(WordCount("dog", 50), WordCount("cow", 60)))
collection.saveAsCassandraTable("test", "words_new", SomeColumns("word", "count"))

To customize the table definition, call saveAsCassandraTableEx. The following example demonstrates how to add another column of int type to the table definition, creating new table words_new_2:

Example Creating a New Table Using the Definition of another Table

import com.datastax.spark.connector.cql.{ColumnDef, RegularColumn, TableDef}
import com.datastax.spark.connector.types.IntType
case class WordCount(word: String, count: Long)
val table1 = TableDef.fromType[WordCount]("test", "words_new")
val table2 = TableDef("test", "words_new_2", table1.partitionKey, table1.clusteringColumns,
  table1.regularColumns :+ ColumnDef("additional_column", RegularColumn, IntType))
val collection = sc.parallelize(Seq(WordCount("dog", 50), WordCount("cow", 60)))
collection.saveAsCassandraTableEx(table2, SomeColumns("word", "count"))

To create a table with a custom definition, and define which columns are to be partition and clustering column keys:

Example Creating a New Table Using a Completely Custom Definition

import com.datastax.spark.connector.cql.{ColumnDef, RegularColumn, TableDef, ClusteringColumn, PartitionKeyColumn}
import com.datastax.spark.connector.types._

// Define structure for rdd data
case class outData(col1:UUID, col2:UUID, col3: Double, col4:Int)

// Define columns
val p1Col = new ColumnDef("col1",PartitionKeyColumn,UUIDType)
val c1Col = new ColumnDef("col2",ClusteringColumn(0),UUIDType)
val c2Col = new ColumnDef("col3",ClusteringColumn(1),DoubleType)
val rCol = new ColumnDef("col4",RegularColumn,IntType)

// Create table definition
val table = TableDef("test","words",Seq(p1Col),Seq(c1Col, c2Col),Seq(rCol))

// Map rdd into custom data structure and create table
val rddOut = rdd.map(s => outData(s._1, s._2(0), s._2(1), s._3))
rddOut.saveAsCassandraTableEx(table, SomeColumns("col1", "col2", "col3", "col4"))

Tuning

For a full listing of Write Tuning Parameters see the reference section Write Tuning Parameters

Next - Customizing the object mapping