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我有一个关闭kafka的流应用程序,我想知道是否有一种方法可以从地图功能内进行范围查询?从火星执行者查询卡桑德拉
我将来自kafka的消息按时间范围和密钥分组,然后基于这些时间范围和密钥我想从cassandra中将数据提取到该dstream中。
喜欢的东西:
lookups
.map(lookup => ((lookup.key, lookup.startTime, lookup.endTime), lookup))
.groupByKey()
.transform(rdd => {
val cassandraSQLContext = new CassandraSQLContext(rdd.context)
rdd.map(lookupPair => {
val tableName = //variable based on lookup
val startTime = aggLookupPair._1._2
val endTime = aggLookupPair._1._3
cassandraSQLContext
.cassandraSql(s"SELECT * FROM ${CASSANDRA_KEYSPACE}.${tableName} WHERE key=${...} AND start_time >= ${startTime} AND start_time < ${endTime};")
.map(row => {
//match to {
case /*case 1*/ => new object1(row)
case /*case 2*/ =>new object2(row)
}
})
.collect()
})
})
这给了我一个空指针异常:
org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 59.0 failed 1 times, most recent failure: Lost task 0.0 in stage 59.0 (TID 63, localhost): java.lang.NullPointerException
at org.apache.spark.sql.SQLContext.parseSql(SQLContext.scala:231)
at org.apache.spark.sql.cassandra.CassandraSQLContext.cassandraSql(CassandraSQLContext.scala:70)
at RollupFineGrainIngestionService$$anonfun$11$$anonfun$apply$2.apply(MyFile.scala:130)
at RollupFineGrainIngestionService$$anonfun$11$$anonfun$apply$2.apply(MyFile.scala:123)
at scala.collection.Iterator$$anon$11.next(Iterator.scala:370)
at org.apache.spark.storage.MemoryStore.unrollSafely(MemoryStore.scala:285)
at org.apache.spark.CacheManager.putInBlockManager(CacheManager.scala:171)
at org.apache.spark.CacheManager.getOrCompute(CacheManager.scala:78)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:268)
at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:306)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:270)
at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:306)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:270)
我也试着ssc.cassandraTable(CASSANDRA_KEYSPACE, tableName).where("key = ?", ...)...
但试图访问一个地图内的StreamingContext时引发崩溃。
如果有人有任何建议,我将不胜感激。谢谢!
我不认为'SparkConf'是可序列化的,我遇到了序列化问题。此外,我试图避免joinWithCassandraTable,因为我不能做范围查询。 – nickn
您可以使用带有JoinWithCassandraTable的范围查询来接受CassandraTableRDD接受的所有子句。 和CassandraConnector是可序列化的 val cc = CassandraConnector(sc.getConf) 然后在任何你喜欢的地方使用cc – RussS
CassandraConnector工作,谢谢! – nickn