Aggregate operations on Azure Cosmos DB for Apache Cassandra tables from Spark

Artikkeli
09/03/2024

APPLIES TO: Cassandra

This article describes basic aggregation operations against Azure Cosmos DB for Apache Cassandra tables from Spark.

Note

Server-side filtering, and server-side aggregation is currently not supported in Azure Cosmos DB for Apache Cassandra.

API for Cassandra configuration

Set below spark configuration in your notebook cluster. It's one time activity.

//Connection-related
 spark.cassandra.connection.host  YOUR_ACCOUNT_NAME.cassandra.cosmosdb.azure.com
 spark.cassandra.connection.port  10350
 spark.cassandra.connection.ssl.enabled  true
 spark.cassandra.auth.username  YOUR_ACCOUNT_NAME
 spark.cassandra.auth.password  YOUR_ACCOUNT_KEY
// if using Spark 2.x
// spark.cassandra.connection.factory  com.microsoft.azure.cosmosdb.cassandra.CosmosDbConnectionFactory

//Throughput-related...adjust as needed
 spark.cassandra.output.batch.size.rows  1
// spark.cassandra.connection.connections_per_executor_max  10   // Spark 2.x
 spark.cassandra.connection.remoteConnectionsPerExecutor  10   // Spark 3.x
 spark.cassandra.output.concurrent.writes  1000
 spark.cassandra.concurrent.reads  512
 spark.cassandra.output.batch.grouping.buffer.size  1000
 spark.cassandra.connection.keep_alive_ms  600000000

Note

If you are using Spark 3.x, you do not need to install the Azure Cosmos DB helper and connection factory. You should also use remoteConnectionsPerExecutor instead of connections_per_executor_max for the Spark 3 connector (see above).

Warning

The Spark 3 samples shown in this article have been tested with Spark version 3.2.1 and the corresponding Cassandra Spark Connector com.datastax.spark:spark-cassandra-connector-assembly_2.12:3.2.0. Later versions of Spark and/or the Cassandra connector might not function as expected.

Sample data generator

import org.apache.spark.sql.cassandra._
//Spark connector
import com.datastax.spark.connector._
import com.datastax.spark.connector.cql.CassandraConnector
import org.apache.spark.sql.functions._

//if using Spark 2.x, CosmosDB library for multiple retry
//import com.microsoft.azure.cosmosdb.cassandra

// Generate a simple dataset containing five values
val booksDF = Seq(
   ("b00001", "Arthur Conan Doyle", "A study in scarlet", 1887,11.33),
   ("b00023", "Arthur Conan Doyle", "A sign of four", 1890,22.45),
   ("b01001", "Arthur Conan Doyle", "The adventures of Sherlock Holmes", 1892,19.83),
   ("b00501", "Arthur Conan Doyle", "The memoirs of Sherlock Holmes", 1893,14.22),
   ("b00300", "Arthur Conan Doyle", "The hounds of Baskerville", 1901,12.25)
).toDF("book_id", "book_author", "book_name", "book_pub_year","book_price")

booksDF.write
  .mode("append")
  .format("org.apache.spark.sql.cassandra")
  .options(Map( "table" -> "books", "keyspace" -> "books_ks", "output.consistency.level" -> "ALL", "ttl" -> "10000000"))
  .save()

Count operation

RDD API

sc.cassandraTable("books_ks", "books").count

Output:

count: Long = 5

Dataframe API

Count against dataframes is currently not supported. The sample below shows how to execute a dataframe count after persisting the dataframe to memory as a workaround.

Choose a storage option from the following available options, to avoid running into "out of memory" issues:

MEMORY_ONLY: It's the default storage option. Stores RDD as deserialized Java objects in the JVM. If the RDD doesn't fit in memory, some partitions won't be cached, and they're recomputed on the fly each time they're needed.
MEMORY_AND_DISK: Stores RDD as deserialized Java objects in the JVM. If the RDD doesn't fit in memory, store the partitions that don't fit on disk, and whenever required, read them from the location they're stored.
MEMORY_ONLY_SER (Java/Scala): Stores RDD as serialized Java objects- 1-byte array per partition. This option is space-efficient when compared to deserialized objects, especially when using a fast serializer, but more CPU-intensive to read.
MEMORY_AND_DISK_SER (Java/Scala): This storage option is like MEMORY_ONLY_SER, the only difference is that it spills partitions that don't fit in the disk memory instead of recomputing them when they're needed.
DISK_ONLY: Stores the RDD partitions on the disk only.
MEMORY_ONLY_2, MEMORY_AND_DISK_2...: Same as the levels above, but replicates each partition on two cluster nodes.
OFF_HEAP (experimental): Similar to MEMORY_ONLY_SER, but it stores the data in off-heap memory, and it requires off-heap memory to be enabled ahead of time.

//Workaround
import org.apache.spark.storage.StorageLevel

//Read from source
val readBooksDF = spark
  .read
  .cassandraFormat("books", "books_ks", "")
  .load()

//Explain plan
readBooksDF.explain

//Materialize the dataframe
readBooksDF.persist(StorageLevel.MEMORY_ONLY)

//Subsequent execution against this DF hits the cache
readBooksDF.count

//Persist as temporary view
readBooksDF.createOrReplaceTempView("books_vw")

SQL

%sql
select * from books_vw;
select count(*) from books_vw where book_pub_year > 1900;
select count(book_id) from books_vw;
select book_author, count(*) as count from books_vw group by book_author;
select count(*) from books_vw;

Average operation

RDD API

sc.cassandraTable("books_ks", "books").select("book_price").as((c: Double) => c).mean

Output:

res24: Double = 16.016000175476073

Dataframe API

spark
  .read
  .cassandraFormat("books", "books_ks", "")
  .load()
  .select("book_price")
  .agg(avg("book_price"))
  .show

Output:

+------------------+
| avg(book_price) |
| +------------------+ |
| 16.016000175476073 |
| +------------------+ |

SQL

select avg(book_price) from books_vw;

Output:

16.016000175476073

Min operation

RDD API

sc.cassandraTable("books_ks", "books").select("book_price").as((c: Float) => c).min

Output:

res31: Float = 11.33

Dataframe API

spark
  .read
  .cassandraFormat("books", "books_ks", "")
  .load()
  .select("book_id","book_price")
  .agg(min("book_price"))
  .show

Output:

+---------------+
| min(book_price) |
| +---------------+ |
| 11.33 |
| +---------------+ |

SQL

%sql
select avg(book_price) from books_vw;

Output:

11.33

Max operation

RDD API

sc.cassandraTable("books_ks", "books").select("book_price").as((c: Float) => c).max

Dataframe API

spark
  .read
  .cassandraFormat("books", "books_ks", "")
  .load()
  .select("book_price")
  .agg(max("book_price"))
  .show

Output:

+---------------+
| max(book_price) |
| +---------------+ |
| 22.45 |
| +---------------+ |

SQL

%sql
select max(book_price) from books_vw;

Output:

22.45

Sum operation

RDD API

sc.cassandraTable("books_ks", "books").select("book_price").as((c: Float) => c).sum

Output:

res46: Double = 80.08000087738037

Dataframe API

spark
  .read
  .cassandraFormat("books", "books_ks", "")
  .load()
  .select("book_price")
  .agg(sum("book_price"))
  .show

Output:

+-----------------+
| sum(book_price) |
| +-----------------+ |
| 80.08000087738037 |
| +-----------------+ |

SQL

select sum(book_price) from books_vw;

Output:

80.08000087738037

Top or comparable operation

RDD API

val readCalcTopRDD = sc.cassandraTable("books_ks", "books").select("book_name","book_price").sortBy(_.getFloat(1), false)
readCalcTopRDD.zipWithIndex.filter(_._2 < 3).collect.foreach(println)
//delivers the first top n items without collecting the rdd to the driver.

Output:

(CassandraRow{book_name: A sign of four, book_price: 22.45},0)
(CassandraRow{book_name: The adventures of Sherlock Holmes, book_price: 19.83},1)
(CassandraRow{book_name: The memoirs of Sherlock Holmes, book_price: 14.22},2)
readCalcTopRDD: org.apache.spark.rdd.RDD[com.datastax.spark.connector.CassandraRow] = MapPartitionsRDD[430] at sortBy at command-2371828989676374:1

Dataframe API

import org.apache.spark.sql.functions._

val readBooksDF = spark.read.format("org.apache.spark.sql.cassandra")
  .options(Map( "table" -> "books", "keyspace" -> "books_ks"))
  .load
  .select("book_name","book_price")
  .orderBy(desc("book_price"))
  .limit(3)

//Explain plan
readBooksDF.explain

//Top
readBooksDF.show

Output:

== Physical Plan ==
TakeOrderedAndProject(limit=3, orderBy=[book_price#1840 DESC NULLS LAST], output=[book_name#1839,book_price#1840])
+- *(1) Scan org.apache.spark.sql.cassandra.CassandraSourceRelation@29cd5f58 [book_name#1839,book_price#1840] PushedFilters: [], ReadSchema: struct<book_name:string,book_price:float>
+--------------------+----------+
| book_name | book_price |
| +--------------------+----------+ |
| A sign of four | 22.45 |
| The adventures of... | 19.83 |
| The memoirs of Sh... | 14.22 |
| +--------------------+----------+ |

import org.apache.spark.sql.functions._
readBooksDF: org.apache.spark.sql.Dataset[org.apache.spark.sql.Row] = [book_name: string, book_price: float]

SQL

select book_name,book_price from books_vw order by book_price desc limit 3;

Next step

Table copy operations

Jaa

Aggregate operations on Azure Cosmos DB for Apache Cassandra tables from Spark

API for Cassandra configuration

Sample data generator

Count operation

RDD API

Dataframe API

SQL

Average operation

RDD API

Dataframe API

SQL

Min operation

RDD API

Dataframe API

SQL

Max operation

RDD API

Dataframe API

SQL

Sum operation

RDD API

Dataframe API

SQL

Top or comparable operation

RDD API

Dataframe API

SQL

Next step

Palaute

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