问题描述
我读到具有相同分区的RDD将位于同一位置.这对我很重要，因为我想加入几个未分区的大型Hive表.我的理论是，如果我可以将它们分区(通过字段调用date_day)并放在同一位置，那么我将避免改组.
I read that RDDs with the same partitioner will be co-located. This is important to me because I want to join several large Hive tables that are not partitioned. My theory is that if I can get them partitioned (by a field call date_day) and co-located then I would avoid shuffling .
这是我要为每个表做的事情:
Here is what I am trying to do for each table:
def date_day_partitioner(key):
return (key.date_day - datetime.date(2017,05,01)).days
df = sqlContext.sql("select * from hive.table")
rdd = df.rdd
rdd2 = rdd.partitionBy(100, date_day_partitioner)
df2 = sqlContext.createDataFrame(rdd2, df_log_entry.schema)
print df2.count()
不幸的是，我什至无法测试关于共址和避免改组的理论，因为在尝试partitionBy时出现以下错误:ValueError:太多的值无法解包
Unfortunately, I can't even test my theory about co-location and avoiding shuffling, because I get the following error when I try partitionBy: ValueError: too many values to unpack
Traceback (most recent call last):
File "/tmp/zeppelin_pyspark-118755547579363441.py", line 346, in <module>
raise Exception(traceback.format_exc())
Exception: Traceback (most recent call last):
File "/tmp/zeppelin_pyspark-118755547579363441.py", line 339, in <module>
exec(code)
File "<stdin>", line 15, in <module>
File "/usr/lib/spark/python/pyspark/sql/dataframe.py", line 380, in count
return int(self._jdf.count())
File "/usr/lib/spark/python/lib/py4j-0.10.4-src.zip/py4j/java_gateway.py", line 1133, in __call__
answer, self.gateway_client, self.target_id, self.name)
File "/usr/lib/spark/python/pyspark/sql/utils.py", line 63, in deco
return f(*a, **kw)
File "/usr/lib/spark/python/lib/py4j-0.10.4-src.zip/py4j/protocol.py", line 319, in get_return_value
format(target_id, ".", name), value)
Py4JJavaError: An error occurred while calling o115.count.
: org.apache.spark.SparkException: Job aborted due to stage failure: Task 21 in stage 6.0 failed 4 times, most recent failure: Lost task 21.3 in stage 6.0 (TID 182, ip-172-31-49-209.ec2.internal, executor 3): org.apache.spark.api.python.PythonException: Traceback (most recent call last):
File "/mnt/yarn/usercache/zeppelin/appcache/application_1509802099365_0013/container_1509802099365_0013_01_000007/pyspark.zip/pyspark/worker.py", line 174, in main
process()
File "/mnt/yarn/usercache/zeppelin/appcache/application_1509802099365_0013/container_1509802099365_0013_01_000007/pyspark.zip/pyspark/worker.py", line 169, in process
serializer.dump_stream(func(split_index, iterator), outfile)
File "/mnt/yarn/usercache/zeppelin/appcache/application_1509802099365_0013/container_1509802099365_0013_01_000007/pyspark.zip/pyspark/serializers.py", line 138, in dump_stream
for obj in iterator:
File "/usr/lib/spark/python/pyspark/rdd.py", line 1752, in add_shuffle_key
ValueError: too many values to unpack
at org.apache.spark.api.python.PythonRunner$$anon$1.read(PythonRDD.scala:193)
at org.apache.spark.api.python.PythonRunner$$anon$1.<init>(PythonRDD.scala:234)
at org.apache.spark.api.python.PythonRunner.compute(PythonRDD.scala:152)
at org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:63)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:323)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:287)
at org.apache.spark.api.python.PairwiseRDD.compute(PythonRDD.scala:390)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:323)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:287)
...
我一定做错了，请您帮忙?
I must be doing something wrong, could you please help?
推荐答案
之所以发生这种情况，是因为您没有在键值对rdd上应用partitionBy.您的rdd必须在键值对中.另外，您的密钥类型应为整数.我没有您的蜂巢表的示例数据.因此，让我们使用以下配置单元表来演示事实:
It's happening because you are not applying partitionBy on key-value pair rdd. Your rdd must be in key-value pair. Also, your key type should be integer. I don't have sample data for your hive table. So let's demonstrate the fact using below hive table:
我已经使用配置单元表创建了以下数据框:
I have created a below dataframe using hive table :
df = spark.table("udb.emp_details_table");
+------+--------+--------+----------------+
|emp_id|emp_name|emp_dept|emp_joining_date|
+------+--------+--------+----------------+
| 1| AAA| HR| 2018-12-06|
| 1| BBB| HR| 2017-10-26|
| 2| XXX| ADMIN| 2018-10-22|
| 2| YYY| ADMIN| 2015-10-19|
| 2| ZZZ| IT| 2018-05-14|
| 3| GGG| HR| 2018-06-30|
+------+--------+--------+----------------+
现在，我希望对数据框进行分区，并希望将相似的密钥保留在一个分区中.因此，我已将数据帧转换为rdd，因为您只能在rdd上应用partitionBy进行重新分区.
Now, I wish to partition my dataframe and want to keep the similar keys in one partition. So, I have converted my dataframe to rdd as you can only apply partitionBy on rdd for re-partitioning.
myrdd = df.rdd
newrdd = myrdd.partitionBy(10,lambda k: int(k[0]))
newrdd.take(10)
我遇到了同样的错误:
File "/usr/hdp/current/spark2-client/python/pyspark/rdd.py", line 1767, in add_shuffle_key
for k, v in iterator:
ValueError: too many values to unpack
因此，我们需要将rdd转换为键值对以使用paritionBy
Hence, we need to convert our rdd into key-value pair to use paritionBy
keypair_rdd = myrdd.map(lambda x : (x[0],x[1:]))
现在，您可以看到rdd已转换为键值对，因此您可以根据可用的键将数据分布在分区中.
Now,you can see that rdd has been converted to key value pair and you can therefore distribute your data in partitions according to keys available.
[(u'1', (u'AAA', u'HR', datetime.date(2018, 12, 6))),
(u'1', (u'BBB', u'HR', datetime.date(2017, 10, 26))),
(u'2', (u'XXX', u'ADMIN', datetime.date(2018, 10, 22))),
(u'2', (u'YYY', u'ADMIN', datetime.date(2015, 10, 19))),
(u'2', (u'ZZZ', u'IT', datetime.date(2018, 5, 14))),
(u'3', (u'GGG', u'HR', datetime.date(2018, 6, 30)))]
现在使用对键值rdd的分区:
Using a paritionBy on key-value rdd now:
newrdd = keypair_rdd.partitionBy(5,lambda k: int(k[0]))
让我们看一下分区.数据已分组，并且类似的密钥现在存储在类似的分区中.其中两个是空的.
Lets take a look at the partitions.Data is grouped and similar keys are stored into similar partitions now. Two of them are empty.
>>> print("Partitions structure: {}".format(newrdd.glom().map(len).collect()))
Partitions structure: [0, 2, 3, 1, 0]
现在可以说我想对数据进行自定义分区.因此，我创建了以下函数，以将键"1"和"3"保持在相似的分区中.
Now lets say I want to custom partitioning my data. So I have created below function to keep keys '1' and '3' in similar partition.
def partitionFunc(key):
import random
if key == 1 or key == 3:
return 0
else:
return random.randint(1,2)
newrdd = keypair_rdd.partitionBy(5,lambda k: partitionFunc(int(k[0])))
>>> print("Partitions structure: {}".format(newrdd.glom().map(len).collect()))
Partitions structure: [3, 3, 0, 0, 0]
现在您可以看到，键1和键3存储在一个分区中，而另一个则存储在另一个分区中.
As you can see now that keys 1 and 3 are stored in one partition and rest on other.
我希望这会有所帮助.您可以尝试按数据框进行分区.确保将其转换为键值对，并将键保持为整数类型.
I hope this helps. You can try to partitionBy your dataframe. Make sure to convert it into key value pair and keeping key as type integer.
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