scala - 线程 # 将 _ GB 的排序数据溢出到磁盘

Question

我正在尝试编写一个 ETL 过程，在联合之前合并两个数据集，我向每个数据集添加一列，较新的数据集获取 2，较旧的数据集获取 1，然后如果行具有重复的主键，我会删除该行旧/新列中有 1。我尝试以多种方式编写此内容，最近通过执行以下操作:

orderBy(keys, desc(old/new)).dropDuplicates(keys)

但是在大​​型数据集上，我总是会出现大幅减速，并显示一条消息:

16/09/21 20:31:45 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (0  time so far)
16/09/21 20:32:00 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (1  time so far)
16/09/21 20:32:16 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (2  times so far)
16/09/21 20:32:31 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (3  times so far)
16/09/21 20:32:47 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (4  times so far)
16/09/21 20:33:02 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (5  times so far)
16/09/21 20:33:18 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (6  times so far)
16/09/21 20:33:33 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (7  times so far)
16/09/21 20:33:49 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (8  times so far)
16/09/21 20:34:04 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (9  times so far)
16/09/21 20:34:19 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (10  times so far)
16/09/21 20:34:35 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (11  times so far)
16/09/21 20:34:50 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (12  times so far)
16/09/21 20:35:06 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (13  times so far)
16/09/21 20:35:21 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (14  times so far)
16/09/21 20:35:37 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (15  times so far)
16/09/21 20:35:52 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (16  times so far)
16/09/21 20:36:07 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (17  times so far)
16/09/21 20:36:23 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (18  times so far)
16/09/21 20:36:38 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (19  times so far)
16/09/21 20:36:53 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (20  times so far)
16/09/21 20:37:09 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (21  times so far)
16/09/21 20:37:24 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (22  times so far)
16/09/21 20:37:40 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (23  times so far)
16/09/21 20:37:55 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (24  times so far)
16/09/21 20:38:10 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (25  times so far)
16/09/21 20:38:25 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (26  times so far)
16/09/21 20:38:41 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (27  times so far)
16/09/21 20:38:56 INFO UnsafeExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (28  times so far)
16/09/21 20:39:25 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (0  time so far)
16/09/21 20:39:45 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (1  time so far)
16/09/21 20:40:05 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (2  times so far)
16/09/21 20:40:26 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (3  times so far)
16/09/21 20:40:46 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (4  times so far)
16/09/21 20:41:07 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (5  times so far)
16/09/21 20:41:27 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (6  times so far)
16/09/21 20:41:47 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (7  times so far)
16/09/21 20:42:07 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (8  times so far)
16/09/21 20:42:28 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (9  times so far)
16/09/21 20:42:49 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (10  times so far)
16/09/21 20:43:09 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (11  times so far)
16/09/21 20:43:30 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (12  times so far)
16/09/21 20:43:50 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (13  times so far)
16/09/21 20:44:11 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (14  times so far)
16/09/21 20:44:31 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (15  times so far)
16/09/21 20:44:52 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (16  times so far)
16/09/21 20:45:13 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (17  times so far)
16/09/21 20:45:33 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (18  times so far)
16/09/21 20:45:53 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (19  times so far)
16/09/21 20:46:14 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (20  times so far)
16/09/21 20:46:34 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (21  times so far)
16/09/21 20:46:54 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (22  times so far)
16/09/21 20:47:14 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (23  times so far)
16/09/21 20:47:34 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (24  times so far)
16/09/21 20:47:54 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (25  times so far)
16/09/21 20:48:14 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (26  times so far)
16/09/21 20:48:34 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (27  times so far)
16/09/21 20:48:54 INFO ShuffleExternalSorter: Thread 84 spilling sort data of 3.0 GB to disk (28  times so far)

检查 Spark UI 后，只有一个线程正在超时工作，而其余线程已经完成。

是否有可能将其分散到线程之间？

Answer 1

您解决此问题的方式在设计上会放大与数据倾斜相关的任何可能的问题。由于您首先按键和指示变量对数据重新排序，因此您首先对数据进行洗牌，可能会创建高度不平衡的分区。此后应用的任何减少都无法弥补这一点。

至少有两种方法可以用来实现相同的结果，同时充分受益于 map 边缩减。我在 SPARK DataFrame: select the first row of each group 的回答中解释了这两点所以重申一下:

• 您可以使用struct排序来选择每组的最小/最大行。
• 您可以将静态类型的Dataset与groupByKey结合使用，后跟reduceGroups。