我正在hadoop上运行一个简单的mapreduce程序,从数据集的一列计算值的min、max、median和stdev。当我在我的计算机上本地运行这个程序时,我会从数据集的所有值计算出最终的输出。然而,当我在hadoop上运行这个时,输出相当于dataset列中几乎一半的值。代码如下:
Map器.py
# !/usr/bin/env python3
import sys
import csv
# Load data
data = csv.DictReader(sys.stdin)
# Prints/Passes key-value to reducer.py
for row in data:
for col, value in row.items():
if col == sys.argv[1]:
print('%s\t%s' % (col, value))
异径管.py
# !/usr/bin/env python3
import sys
import statistics
key = None
current_key = None
num_list = []
for line in sys.stdin:
# Remove leading and trailng whitespace
line = line.strip()
# Parse input
key, value = line.split('\t', 1)
# Convert string to int
try:
value = float(value)
except ValueError:
# Skip the value
continue
if current_key == key:
num_list.append(value)
else:
if current_key:
print("Num. of Data Points %s\t --> Max: %s\t Min: %s\t Median: %s\t Standard Deviation: %s" \
% (len(num_list), max(num_list), min(num_list), statistics.median(num_list), statistics.pstdev(num_list)))
num_list.clear()
num_list.append(value)
current_key = key
# Output last value if needed
if current_key == key:
print("Num. of Data Points %s\t --> Max: %s\t Min: %s\t Median: %s\t Standard Deviation: %s" \
% (len(num_list), max(num_list), min(num_list), statistics.median(num_list), statistics.pstdev(num_list)))
haddop日志:
2019-12-02 23:54:40,705 INFO mapreduce.Job: Running job: job_1575141442909_0026
2019-12-02 23:54:47,903 INFO mapreduce.Job: Job job_1575141442909_0026 running in uber mode : false
2019-12-02 23:54:47,906 INFO mapreduce.Job: map 0% reduce 0%
2019-12-02 23:54:54,019 INFO mapreduce.Job: map 100% reduce 0%
2019-12-02 23:54:59,076 INFO mapreduce.Job: map 100% reduce 100%
2019-12-02 23:55:00,115 INFO mapreduce.Job: Job job_1575141442909_0026 completed successfully
2019-12-02 23:55:00,253 INFO mapreduce.Job: Counters: 54
File System Counters
FILE: Number of bytes read=139868
FILE: Number of bytes written=968967
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=501097
HDFS: Number of bytes written=114
HDFS: Number of read operations=11
HDFS: Number of large read operations=0
HDFS: Number of write operations=2
HDFS: Number of bytes read erasure-coded=0
Job Counters
Launched map tasks=2
Launched reduce tasks=1
Data-local map tasks=2
Total time spent by all maps in occupied slots (ms)=7492
Total time spent by all reduces in occupied slots (ms)=2767
Total time spent by all map tasks (ms)=7492
Total time spent by all reduce tasks (ms)=2767
Total vcore-milliseconds taken by all map tasks=7492
Total vcore-milliseconds taken by all reduce tasks=2767
Total megabyte-milliseconds taken by all map tasks=7671808
Total megabyte-milliseconds taken by all reduce tasks=2833408
Map-Reduce Framework
Map input records=10408
Map output records=5203
Map output bytes=129456
Map output materialized bytes=139874
Input split bytes=220
Combine input records=0
Combine output records=0
Reduce input groups=1
Reduce shuffle bytes=139874
Reduce input records=5203
Reduce output records=1
Spilled Records=10406
Shuffled Maps =2
Failed Shuffles=0
Merged Map outputs=2
GC time elapsed (ms)=80
CPU time spent (ms)=2790
Physical memory (bytes) snapshot=676896768
Virtual memory (bytes) snapshot=8266964992
Total committed heap usage (bytes)=482344960
Peak Map Physical memory (bytes)=253210624
Peak Map Virtual memory (bytes)=2755108864
Peak Reduce Physical memory (bytes)=173010944
Peak Reduce Virtual memory (bytes)=2758103040
Shuffle Errors
BAD_ID=0
CONNECTION=0
IO_ERROR=0
WRONG_LENGTH=0
WRONG_MAP=0
WRONG_REDUCE=0
File Input Format Counters
Bytes Read=500877
File Output Format Counters
Bytes Written=114
2019-12-02 23:55:00,254 INFO streaming.StreamJob: Output directory: data/output
本地输出:
# Data Points: 10407 Max: 89.77682042 Min: 13.87331897 Median: 46.44807153 Standard Deviation: 11.156280347146872
hadoop输出:
# Data Points: 5203 Max: 89.77682042 Min: 13.87331897 Median: 46.202181 Standard Deviation: 11.28118280525746
正如您所看到的,hadoop输出中的数据点数量几乎正好是本地输出中全部数据点数量的一半。我试着使用不同大小的不同数据集,结果总是一半…我是做错了什么还是遗漏了什么?
1条答案
按热度按时间ukqbszuj1#
我已经弄明白了为什么我会得到这样的结果。原因是因为hadoop将我的输入数据一分为二,用于两个独立的Map器,正如我所怀疑的那样。但是,只有数据的前半部分保留了数据集的列标题,因此,当Map程序读取数据集的后半部分时,将不会访问指定的列。
我从数据集中删除了现有的头,并在读取数据时设置了字段名,以便解决问题: