Merging multiple files into one within Hadoop

hadoop apache-pig
uHadoop picture uHadoop · Aug 23, 2010 · Viewed 47.5k times · Source

I get multiple small files into my input directory which I want to merge into a single file without using the local file system or writing mapreds. Is there a way I could do it using hadoof fs commands or Pig?

Thanks!

Answer

Guy B picture Guy B · Nov 25, 2014

In order to keep everything on the grid use hadoop streaming with a single reducer and cat as the mapper and reducer (basically a noop) - add compression using MR flags.

hadoop jar \
    $HADOOP_PREFIX/share/hadoop/tools/lib/hadoop-streaming.jar \<br>
    -Dmapred.reduce.tasks=1 \
    -Dmapred.job.queue.name=$QUEUE \
    -input "$INPUT" \
    -output "$OUTPUT" \
    -mapper cat \
    -reducer cat

If you want compression add
-Dmapred.output.compress=true \ -Dmapred.output.compression.codec=org.apache.hadoop.io.compress.GzipCodec

Related questions

Difference between Pig and Hive? Why have both?

My background - 4 weeks old in the Hadoop world. Dabbled a bit in Hive, Pig and Hadoop using Cloudera's Hadoop VM. Have read Google's paper on Map-Reduce and GFS (PDF link). I understand that- Pig's language Pig Latin is a …

Read More
When to use Hadoop, HBase, Hive and Pig?

What are the benefits of using either Hadoop or HBase or Hive ? From my understanding, HBase avoids using map-reduce and has a column oriented storage on top of HDFS. Hive is a sql-like interface for Hadoop and HBase. I would …

Read More
PIG how to count a number of rows in alias

I did something like this to count the number of rows in an alias in PIG: logs = LOAD 'log' logs_w_one = foreach logs generate 1 as one; logs_group = group logs_w_one all; logs_count = foreach logs_group generate …

Read More