[MAPREDUCE-491] RAgzip: multiple map tasks for a large gzipped file

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Assignee: Daehyun Kim
• Reporter: Daehyun Kim
• Created: 13/Nov/08 10:00
• Updated: 23/Jul/14 19:53

Description

Currently, the hadoop processes gzipped files with only one map.
We have made a patch that enables multiple map tasks for one large gzipped file. We call the patch RAgzip.
To process multiple map tasks for gzipped file, you may use RAgzip by just changing InputFormat to RAGZIPInputFormat.
The option used in RAGZIPInputFormat can be found at the javadoc of RAGZIPInputFormat part.

RAgzip uses zlib's inflatePrime function which supports random access on a gzipped file.
Since the inflatePrime is supported from the version of 1.2.2.4, it requires zlib 1.2.2.4 or higher. (We tested on zlib 1.2.3)
RAgzip requires the preprocessing step that creates an access point (.ap) file, which is like the index of the gzipped file chunks.
The access point(.ap) file is located in same path of the gzipped file.
If there is a "/user/hadoop/test.gz", the .ap file is created with "/user/hadoop/test.gz.ap".

Issue Links

• depends upon: HADOOP-3020 Nightly and Patch builds should include native, c++, and eclipse-contrib
• duplicates: HADOOP-6153 RAgzip: multiple map tasks for a large gzipped file