星火:如何使用mapPartition并创建每个分区/关闭连接 [英] Spark : How to use mapPartition and create/close connection per partition
问题描述
所以,我想对我的火花数据框中指定的工作,他们写信给DB和创造末另一个数据框。它看起来是这样的:
So, I want to do certain operations on my spark DataFrame, write them to DB and create another DataFrame at the end. It looks like this :
import sqlContext.implicits._
val newDF = myDF.mapPartitions(
iterator => {
val conn = new DbConnection
iterator.map(
row => {
addRowToBatch(row)
convertRowToObject(row)
})
conn.writeTheBatchToDB()
conn.close()
})
.toDF()
这给了我一个错误mapPartitions预计返回类型的Iterator [NotInferedR]
,但在这里它是单位
。我知道这是可能的forEachPartition,但我喜欢做的映射也。这样做分开将是一个开销(额外的火花的工作)。怎么办?
This gives me an error as mapPartitions expects return type of Iterator[NotInferedR]
, but here it is Unit
. I know this is possible with forEachPartition, but I'd like to do the mapping also. Doing it separate would be an overhead (extra spark job). What to do?
谢谢!
推荐答案
在匿名函数执行的最后一个前pression必须返回值:
The last expression in the anonymous function implementation must be the return value:
import sqlContext.implicits._
val newDF = myDF.mapPartitions(
iterator => {
val conn = new DbConnection
val result = iterator.map(/* the same... */)
conn.writeTheBatchToDB()
conn.close()
result
}
).toDF()
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