如何计算 Spark 中数据帧的大小（以字节为单位）？

Question

我想编写一个带有重新分区的大型数据帧，所以我想计算源数据帧的重新分区数量。

numberofpartition = {size of dataframe/default_blocksize}

如何计算数据帧大小（以字节为单位）？

Answer 1

使用

spark.sessionState.executePlan(df.queryExecution.logical).optimizedPlan.stats(spark.sessionState.conf).sizeInBytes

我们可以在加载到内存后获取实际Dataframe的大小。检查下面的代码。

scala> val df = spark.read.format("orc").load("/tmp/srinivas/")
df: org.apache.spark.sql.DataFrame = [channelGrouping: string, clientId: string ... 75 more fields]

scala> import org.apache.commons.io.FileUtils
import org.apache.commons.io.FileUtils

scala> val bytes = spark.sessionState.executePlan(df.queryExecution.logical).optimizedPlan.stats(spark.sessionState.conf).sizeInBytes
bytes: BigInt = 763275709

scala> FileUtils.byteCountToDisplaySize(bytes.toLong)
res5: String = 727 MB

scala> import sys.process._
import sys.process._

scala> "hdfs dfs -ls -h /tmp/srinivas/".!
Found 2 items
-rw-r-----   3 svcmxns hdfs          0 2020-04-20 01:46 /tmp/srinivas/_SUCCESS
-rw-r-----   3 svcmxns hdfs    727.4 M 2020-04-20 01:46 /tmp/srinivas/part-00000-9d0b72ea-f617-4092-ae27-d36400c17917-c000.snappy.orc
res6: Int = 0

val bytes = spark.sessionState.executePlan(df.queryExecution.logical).optimizedPlan.stats(spark.sessionState.conf).sizeInBytes
    val dataSize = bytes.toLong
    val numPartitions = (bytes.toLong./(1024.0)./(1024.0)./(10240)).ceil.toInt // May be you can change or modify this to get required partitions.

    df.repartition(if(numPartitions == 0) 1 else numPartitions)
      .[...]

Edit - 1

：请根据您的 Spark 版本使用以下逻辑。

Spark 3.0.2

val bytes = spark.sessionState.executePlan(df.queryExecution.logical).optimizedPlan.stats.sizeInBytes

星火2.4

val bytes = spark.sessionState.executePlan(df.queryExecution.logical).optimizedPlan.stats(spark.sessionState.conf).sizeInBytes

星火2.3

val bytes = spark.sessionState.executePlan(df.queryExecution.logical).optimizedPlan.stats.sizeInBytes

PySpark

spark._jsparkSession.sessionState().executePlan(df._jdf.queryExecution().logical()).optimizedPlan().stats().sizeInBytes()