Gzipping Har Files on HDFS using Spark - scala

Question

I have huge data in hadoop archive .har format. Since, har doesn't include any compression, I am trying to further gzip it in and store in HDFS. The only thing I can get to work without error is :
harFile.coalesce(1, "true")
.saveAsTextFile("hdfs://namenode/archive/GzipOutput", classOf[org.apache.hadoop.io.compress.GzipCodec])
//`coalesce` because Gzip isn't splittable.
But, this doesn't give me the correct results. A Gzipped file is generated but with invalid output ( a single line saying the rdd type etc.)
Any help will be appreciated. I am also open to any other approaches.
Thanks.

Answer 1

A Java code snippet to create a compressed version of an existing HDFS file.
Built in a hurry, in a text editor, from bits and pieces of a Java app I wrote some time ago, hence not tested; some typos and gaps to be expected.
// HDFS API
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.security.UserGroupInformation;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.FileStatus;
// native Hadoop compression libraries
import org.apache.hadoop.io.compress.CompressionCodecFactory;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.Compressor;
import org.apache.hadoop.io.compress.GzipCodec;
import org.apache.hadoop.io.compress.BZip2Codec;
import org.apache.hadoop.io.compress.SnappyCodec;
import org.apache.hadoop.io.compress.Lz4Codec;
..............
// Hadoop "Configuration" (and its derivatives for HDFS, HBase etc.) constructors try to auto-magically
// find their config files by searching CLASSPATH for directories, and searching each dir for hard-coded
// name "core-site.xml", plus "hdfs-site.xml" and/or "hbase-site.xml" etc.
// WARNING - if these config files are not found, the "Configuration" reverts to hard-coded defaults without
// any warning, resulting in bizarre error messages later > let's run some explicit controls here
Configuration cnfHadoop = new Configuration() ;
String propDefaultFs =cnfHadoop.get("fs.defaultFS") ;
if (propDefaultFs ==null || ! propDefaultFs.startsWith("hdfs://"))
{ throw new IllegalArgumentException(
"HDFS configuration is missing - no proper \"core-site.xml\" found, please add\n"
+"directory /etc/hadoop/conf/ (or custom dir with custom XML conf files) in CLASSPATH"
) ;
}
/*
// for a Kerberised cluster, either you already have a valid TGT in the default
// ticket cache (via "kinit"), or you have to authenticate by code
UserGroupInformation.setConfiguration(cnfHadoop) ;
UserGroupInformation.loginUserFromKeytab("user#REALM", "/some/path/to/user.keytab") ;
*/
FileSystem fsCluster =FileSystem.get(cnfHadoop) ;
Path source = new Path("/some/hdfs/path/to/XXX.har") ;
Path target = new Path("/some/hdfs/path/to/XXX.har.gz") ;
// alternative: "BZip2Codec" for better compression (but higher CPU cost)
// alternative: "SnappyCodec" or "Lz4Codec" for lower compression (but much lower CPU cost)
CompressionCodecFactory codecBootstrap = new CompressionCodecFactory(cnfHadoop) ;
CompressionCodec codecHadoop =codecBootstrap.getCodecByClassName(GzipCodec.class.getName()) ;
Compressor compressorHadoop =codecHadoop.createCompressor() ;
byte[] buffer = new byte[16*1024*1024] ;
int bufUsedCapacity ;
InputStream sourceStream =fsCluster.open(source) ;
OutputStream targetStream =codecHadoop.createOutputStream(fsCluster.create(target, true), compressorHadoop) ;
while ((bufUsedCapacity =sourceStream.read(buffer)) >0)
{ targetStream.write(buffer, 0, bufUsedCapacity) ; }
targetStream.close() ;
sourceStream.close() ;
..............