问题
I am trying to read messages from Kafka, process the data, and then add the data into cassandra as if it is an RDD.
My trouble is saving the data back into cassandra.
from __future__ import print_function
from pyspark.streaming import StreamingContext
from pyspark.streaming.kafka import KafkaUtils
from pyspark import SparkConf, SparkContext
appName = 'Kafka_Cassandra_Test'
kafkaBrokers = '1.2.3.4:9092'
topic = 'test'
cassandraHosts = '1,2,3'
sparkMaster = 'spark://mysparkmaster:7077'
if __name__ == "__main__":
conf = SparkConf()
conf.set('spark.cassandra.connection.host', cassandraHosts)
sc = SparkContext(sparkMaster, appName, conf=conf)
ssc = StreamingContext(sc, 1)
kvs = KafkaUtils.createDirectStream(ssc, [topic], {"metadata.broker.list": kafkaBrokers})
lines = kvs.map(lambda x: x[1])
counts = lines.flatMap(lambda line: line.split(" ")) \
.map(lambda word: (word, 1)) \
.reduceByKey(lambda a, b: a+b)
counts.saveToCassandra('coreglead_v2', 'wordcount')
ssc.start()
ssc.awaitTermination()
And the error:
[root@gasweb2 ~]# spark-submit --jars /var/spark/lib/spark-streaming-kafka-assembly_2.10-1.6.0.jar --packages datastax:spark-cassandra-connector:1.5.0-RC1-s_2.11 /var/spark/scripts/kafka_cassandra.py
Ivy Default Cache set to: /root/.ivy2/cache
The jars for the packages stored in: /root/.ivy2/jars
:: loading settings :: url = jar:file:/var/spark/lib/spark-assembly-1.6.0-hadoop2.6.0.jar!/org/apache/ivy/core/settings/ivysettings.xml
datastax#spark-cassandra-connector added as a dependency
:: resolving dependencies :: org.apache.spark#spark-submit-parent;1.0
confs: [default]
found datastax#spark-cassandra-connector;1.5.0-RC1-s_2.11 in spark-packages
found org.apache.cassandra#cassandra-clientutil;2.2.2 in central
found com.datastax.cassandra#cassandra-driver-core;3.0.0-rc1 in central
found io.netty#netty-handler;4.0.33.Final in central
found io.netty#netty-buffer;4.0.33.Final in central
found io.netty#netty-common;4.0.33.Final in central
found io.netty#netty-transport;4.0.33.Final in central
found io.netty#netty-codec;4.0.33.Final in central
found io.dropwizard.metrics#metrics-core;3.1.2 in central
found org.slf4j#slf4j-api;1.7.7 in central
found org.apache.commons#commons-lang3;3.3.2 in central
found com.google.guava#guava;16.0.1 in central
found org.joda#joda-convert;1.2 in central
found joda-time#joda-time;2.3 in central
found com.twitter#jsr166e;1.1.0 in central
found org.scala-lang#scala-reflect;2.11.7 in central
:: resolution report :: resolve 647ms :: artifacts dl 15ms
:: modules in use:
com.datastax.cassandra#cassandra-driver-core;3.0.0-rc1 from central in [default]
com.google.guava#guava;16.0.1 from central in [default]
com.twitter#jsr166e;1.1.0 from central in [default]
datastax#spark-cassandra-connector;1.5.0-RC1-s_2.11 from spark-packages in [default]
io.dropwizard.metrics#metrics-core;3.1.2 from central in [default]
io.netty#netty-buffer;4.0.33.Final from central in [default]
io.netty#netty-codec;4.0.33.Final from central in [default]
io.netty#netty-common;4.0.33.Final from central in [default]
io.netty#netty-handler;4.0.33.Final from central in [default]
io.netty#netty-transport;4.0.33.Final from central in [default]
joda-time#joda-time;2.3 from central in [default]
org.apache.cassandra#cassandra-clientutil;2.2.2 from central in [default]
org.apache.commons#commons-lang3;3.3.2 from central in [default]
org.joda#joda-convert;1.2 from central in [default]
org.scala-lang#scala-reflect;2.11.7 from central in [default]
org.slf4j#slf4j-api;1.7.7 from central in [default]
---------------------------------------------------------------------
| | modules || artifacts |
| conf | number| search|dwnlded|evicted|| number|dwnlded|
---------------------------------------------------------------------
| default | 16 | 0 | 0 | 0 || 16 | 0 |
---------------------------------------------------------------------
:: retrieving :: org.apache.spark#spark-submit-parent
confs: [default]
0 artifacts copied, 16 already retrieved (0kB/14ms)
16/02/15 16:26:14 WARN NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Traceback (most recent call last):
File "/var/spark/scripts/kafka_cassandra.py", line 27, in <module>
counts.saveToCassandra('coreglead_v2', 'wordcount')
AttributeError: 'TransformedDStream' object has no attribute 'saveToCassandra'
From searching around I have found this GitHub issue, however this seems to be related to a different library (I can't use this library as I am using Cassandra 3.0 and it is not supported yet).
The goal is to create aggregated data from a single message (the wordcount is just for testing) and insert it into several tables.
I am close to just using the Datastax Python Driver and writing the statements myself, but is there a better way to achieve this?
回答1:
You're using the Spark Cassandra Connector by Datastax which doesn't have support for python at the RDD / DStream level. Only Dataframes are supported. See the docs for more information.
I've authored a wrapper around the aforementioned connector: PySpark Cassandra. It is not feature complete with respect to the connector by Datastax, but a lot of stuff is there. Also, if performance is important, investigating the performance hit may be worth while.
Finally, Spark ships with a python example of using the CqlInput/OutputFormat from hadoop mapreduce. Not a very developer friendly option in my opinion, but it's there.
回答2:
Looking at your code and readint through your issue description: it doesn't appear that there is any Cassandra connector that you're using. Spark doesn't come with Cassandra support out of the box as such the RDD and DStream data types don't have the saveToCassandra method. You need to import an external Spark-Cassandra connector which extends the RDD and DStream types to support Cassandra integration.
This is why you're getting the error: Python can't find any function saveToCassandra on the DStream type because none currently exists.
You'll need to get the DataStax connector or some other connector to extend the DStream type with saveToCassandra.
来源：https://stackoverflow.com/questions/35414677/saving-data-back-into-cassandra-as-rdd