How do I combine small files in HDFS?

1. select all files that are ripe for compaction (define your own criteria) and move them from new_data directory to reorg.
2. merge the content of all these reorg files, into a new file in history dir (feel free to GZip it on the fly, Hive will recognize the .
3. drop the files in reorg.

How do I merge files in hive?

Below 4 parameters determine if and how Hive does small file merge.

1. merge. mapfiles — Merge small files at the end of a map-only job.
2. merge. mapredfiles — Merge small files at the end of a map-reduce job.
3. merge. size. per.
4. merge. smallfiles.

How do I combine spark files?

1. Write a Single file using Spark coalesce() & repartition() When you are ready to write a DataFrame, first use Spark repartition() and coalesce() to merge data from all partitions into a single partition and then save it to a file.

Can files in HDFS be modified?

You can not modified data once stored in hdfs because hdfs follows Write Once Read Many model. You can only append the data once stored in hdfs.

How do I merge ORC files?

As of Hive 0.14, users can request an efficient merge of small ORC files together by issuing a CONCATENATE command on their table or partition. The files will be merged at the stripe level without reserialization.

How do I merge small files in Hive table?

If not anyone of the below things should be enable to merge a reducer output if the size is less than an block size.

1. merge. mapfiles — Merge small files at the end of a map-only job.
2. merge. mapredfiles — Merge small files at the end of a map-reduce job.
3. merge. size. per.
4. merge. smallfiles.

What does MSCK repair table do?

MSCK REPAIR TABLE recovers all the partitions in the directory of a table and updates the Hive metastore. When creating a table using PARTITIONED BY clause, partitions are generated and registered in the Hive metastore. User needs to run MSCK REPAIR TABLE to register the partitions.

How do I merge csv files in Pyspark?

1 Answer

1. Do the following things:
2. Create a new DataFrame(headerDF) containing header names.
3. Union it with the DataFrame(dataDF) containing the data.
4. Output the union-ed DataFrame to disk with option(“header”, “false”).
5. 4.merge partition files(part-0000**0.csv) using hadoop FileUtil.

What is ORC format?

The Optimized Row Columnar (ORC) file format provides a highly efficient way to store Hive data. It was designed to overcome limitations of the other Hive file formats. Using ORC files improves performance when Hive is reading, writing, and processing data.

How to merge multiple files into a single file on HDFS?

If you wish to merge all files into a single file on HDFS, run the job with just 1 reducer. If, on the other hand, you want to partition your files into more parts, run the job with more reducers.

How do I merge files in Hadoop without copying them?

Although there is no way of merging files without copying them down locally using the built-in hadoop commands, you can write a trivial mapreduce tool that uses the IdentityMapper and IdentityReducer to re-partition your files. If you wish to merge all files into a single file on HDFS, run the job with just 1 reducer.

How do I merge multiple files into one file in Linux?

One solution is to merge all the files first and then copy the combined file into HDFS (Hadoop Distributed File System) using linux/unix commands line utilities (ex.getmerge command) for merging a number of files before copying them into HDFS.

Is there a reducer for HDFS map?

Offcourse there is no reducer, writing this as an HDFS map task is efficient because it can merge these files into one output file without much data movement across data nodes. As the source files are in HDFS, and since mapper tasks will try data affinity, it can merge files without moving files across different data nodes.