AggregateByKey分区?

问题描述

我有:

A_RDD = anRDD.map()

B_RDD = A_RDD.aggregateByKey()

好的，我的问题是:

如果我在A_RDD之后放置partitionBy(new HashPartitioner)，如下所示:

If i put partitionBy(new HashPartitioner) after A_RDD like :

A_RDD = anRDD.map().partitionBy(new HashPartitioner(2))

B_RDD = A_RDD.aggregateByKey()

1)首先，这会和我将其保持原样一样有效率吗?AggregateByKey()将使用A_RDD中的hashPartitioner，对吗?

1)Will this be the same efficient as if i leave it as it is, in the first place?aggregateByKey() will use that hashPartitioner from A_RDD, right?

2)或者，如果我像在第一个示例中那样保留它，则aggregateByKey()将首先按键聚合每个分区，然后以更多的方式发送每个已聚合"(键，值)对正确的分区的有效方法?

2)Or If i leave it as in the first example,aggregateByKey() will aggregate every partition by key first, and then send every "aggregated" (key, value) pair in a more efficient way to the right partition?

3)为什么RDD上的map，flatMap和其他转换不能接受关于如何动态分配(键，值)对的争论?我的意思是例如在每个元组的map()操作期间，让=>将此元组也发送到特定分区已由地图e.x上的partitioner参数指定的地图:map(，Partitioner).

3)Why doesn't map,flatMap and other transformations on RDDs canNOT take an argument on how to partition the (key, value) pairs on the fly?What I mean is for example during the map() operation on every tuple lets say, => to send also this tuple to a specific partitionthat has been designated by a partitioner argument on map e.x: map( , Partitioner).

我正在尝试掌握AggregateByKey()的工作原理，但是每当我认为得到这一点时，就会出现一个新问题……预先感谢.

I am trying to grasp the concept of aggregateByKey() how it works, but every time i think i got this, a new question arises...Thanks in advance.

推荐答案

• 如果将partitionBy放在aggregateByKey之前，通常效率不如单独使用aggregateByKey.您可以有效地禁用地图侧合并.
• 如果您离开，将会有地图侧联合收割机，而且通常更高效.
• 非改组操作不会占用分区，因为没有数据移动.操作在每台计算机上本地执行.
• If you put partitionBy before aggregateByKey it typically will be less efficient than aggregateByKey alone. You effectively disable map side combine.
• If you leave there will be map side combine and it is typically more efficient.
• Non shuffling operations don't take partitioner because there is no data movement. Operations are performed locally on each machine.

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