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MapReduce, mail # user - Re: How to compress MapFile programmatically


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Re: How to compress MapFile programmatically
Harsh J 2013-08-11, 15:22
A MapFile.Reader will automatically detect and decompress without
needing to be told anything special. You needn't have to worry about
decompressing files by yourself in Apache Hadoop generally - the
framework handles it for you transparently if you're using the proper APIs.

On Sun, Aug 11, 2013 at 8:49 PM, Abhijit Sarkar
<[EMAIL PROTECTED]> wrote:
> Thanks Harsh. However, if I compress the MapFile using the MapFile.Writer
> Constructor option and then put it in a DistributedCache, how do I
> uncompress it in the Map/Reduce? There isn't any API method to do that
> apparently.
>
> Regards,
> Abhijit
>
>> From: [EMAIL PROTECTED]
>> Date: Sun, 11 Aug 2013 12:56:43 +0530
>> Subject: Re: How to compress MapFile programmatically
>> To: [EMAIL PROTECTED]
>
>>
>> A MapFile isn't a directory. It is a directory _containing_ two files.
>> You cannot "open" a directory for reading.
>>
>> The MapFile API is documented at
>> http://hadoop.apache.org/docs/stable/api/org/apache/hadoop/io/MapFile.html
>> and thats what you're to be using for reading/writing them.
>>
>> Compression is a simple option you need to provide when invoking the
>> writer:
>> http://hadoop.apache.org/docs/stable/api/org/apache/hadoop/io/MapFile.Writer.html#MapFile.Writer(org.apache.hadoop.conf.Configuration,%20org.apache.hadoop.fs.FileSystem,%20java.lang.String,%20org.apache.hadoop.io.WritableComparator,%20java.lang.Class,%20org.apache.hadoop.io.SequenceFile.CompressionType,%20org.apache.hadoop.io.compress.CompressionCodec,%20org.apache.hadoop.util.Progressable)
>>
>> On Sun, Aug 11, 2013 at 1:46 AM, Abhijit Sarkar
>> <[EMAIL PROTECTED]> wrote:
>> > Hi,
>> > I'm a Hadoop newbie. This is my first question to this mailing list,
>> > hoping
>> > for a good start :)
>> >
>> > MapFile is a directory so when I try to open an InputStream to it, it
>> > fails
>> > with FileNotFoundException. How do I compress MapFile programmatically?
>> >
>> > Code snippet:
>> > final FileSystem fs = FileSystem.get(conf);
>> > final InputStream inputStream = fs.open(new Path(uncompressedStr));
>> >
>> > Exception:
>> > java.io.FileNotFoundException: /some/directory (No such file or
>> > directory)
>> > at java.io.FileInputStream.open(Native Method)
>> > at java.io.FileInputStream.<init>(FileInputStream.java:120)
>> > at
>> >
>> > org.apache.hadoop.fs.RawLocalFileSystem$TrackingFileInputStream.<init>(RawLocalFileSystem.java:71)
>> > at
>> >
>> > org.apache.hadoop.fs.RawLocalFileSystem$LocalFSFileInputStream.<init>(RawLocalFileSystem.java:107)
>> > at
>> > org.apache.hadoop.fs.RawLocalFileSystem.open(RawLocalFileSystem.java:177)
>> > at
>> >
>> > org.apache.hadoop.fs.ChecksumFileSystem$ChecksumFSInputChecker.<init>(ChecksumFileSystem.java:126)
>> > at
>> > org.apache.hadoop.fs.ChecksumFileSystem.open(ChecksumFileSystem.java:283)
>> > at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:427)
>> > at
>> > name.abhijitsarkar.learning.hadoop.io.IOUtils.compress(IOUtils.java:104)
>> >
>> > Regards,
>> > Abhijit
>>
>>
>>
>> --
>> Harsh J

--
Harsh J