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MapReduce, mail # user - Question related to Decompressor interface


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RE: Question related to Decompressor interface
java8964 java8964 2013-02-10, 15:13

Hi, Dave:
Thanks for you reply. I am not sure how the EncryptedWritable will work, can you share more ideas about it?
For example, if I have a text file as my source raw file. Now I need to store it in HDFS. If I use any encryption to encrypt the whole file, then there is no good InputFormat or RecordReader to process it, unless whole file is decrypted first at runtime, then using TextInputFormat to process it, right?
What you suggest is  when I encrypted the file, store it as a SequenceFile, using anything I want as the key, then encrypt each line (Record), and stores it as the value, put both (key, value) pair into the sequence file, is that right?
Then in the runtime, each value can be decrypted from the sequence file, and ready for next step in the by the EncryptedWritable class. Is my understanding correct?
 In this case, of course I don't need to worry about split any more, as each record is encrypted/decrypted separately.
I think it is a valid option, but problem is that the data has to be encrypted by this EncryptedWritable class. What I was thinking about is allow data source to encrypt its data any way they want, as long as it is supported by Java security package, then only provide the private key to the runtime to decrypt it.
Yong

From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: RE: Question related to Decompressor interface
Date: Sun, 10 Feb 2013 09:36:40 +0700

I can’t answer your question about the Decompressor interface, but I have a query for you. Why not just create an EncryptedWritable object? Encrypt/decrypt the bytes on the read/write method, that should be darn near trivial. Then stick with good ‘ol SequenceFile, which, as you note, is splittable. Otherwise you’d have to deal with making the output splittable, and given encrypted data, the only solution that I see is basically rolling your own SequenceFile with encrypted innards.  Come to think of it, a simple, standardized EncryptedWritable object out of the box with Hadoop would be great. Or perhaps better yet, an EncryptedWritableWrapper<T extends Writable> so we can convert any existing Writable into an encrypted form. Dave  From: java8964 java8964 [mailto:[EMAIL PROTECTED]]
Sent: Sunday, February 10, 2013 3:50 AM
To: [EMAIL PROTECTED]
Subject: Question related to Decompressor interface HI,  Currently I am researching about options of encrypting the data in the MapReduce, as we plan to use the Amazon EMR or EC2 services for our data. I am thinking that the compression codec is good place to integrate with the encryption logic, and I found out there are some people having the same idea as mine. I google around and found out this code: https://github.com/geisbruch/HadoopCryptoCompressor/ It doesn't seem maintained any more, but it gave me a starting point. I download the source code, and try to do some tests with it. It doesn't work out of box. There are some bugs I have to fix to make it work. I believe it contains 'AES' as an example algorithm. But right now, I faced a problem when I tried to use it in my testing MapReduer program. Here is the stack trace I got: 2013-02-08 23:16:47,038 INFO org.apache.hadoop.io.compress.crypto.CryptoBasicDecompressor: buf length = 512, and offset = 0, length = -132967308java.lang.IndexOutOfBoundsException    at java.nio.ByteBuffer.wrap(ByteBuffer.java:352)    at org.apache.hadoop.io.compress.crypto.CryptoBasicDecompressor.setInput(CryptoBasicDecompressor.java:100)    at org.apache.hadoop.io.compress.BlockDecompressorStream.decompress(BlockDecompressorStream.java:97)    at org.apache.hadoop.io.compress.DecompressorStream.read(DecompressorStream.java:83)    at java.io.InputStream.read(InputStream.java:82)    at org.apache.hadoop.util.LineReader.readDefaultLine(LineReader.java:209)    at org.apache.hadoop.util.LineReader.readLine(LineReader.java:173)    at org.apache.hadoop.mapreduce.lib.input.LineRecordReader.nextKeyValue(LineRecordReader.java:114)    at org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:458)    at org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue(MapContextImpl.java:76)    at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue(WrappedMapper.java:85)    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:139)    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:645)    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:325)    at org.apache.hadoop.mapred.Child$4.run(Child.java:268)    at java.security.AccessController.doPrivileged(Native Method)    at javax.security.auth.Subject.doAs(Subject.java:396)    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1332)    at org.apache.hadoop.mapred.Child.main(Child.java:262) I know the error is thrown out of this custom CryptoBasicDecompressor class, but I really have questions related to the interface it implemented: Decompressor. There is limited document about this interface, for example, when and how the method setInput() will be invoked. If I want to write my own Decompressor, what do these methods mean in the interface?In the above case, I enable some debug information, you can see that in this case, the byte[] array passed to setInput method, only have 512 as the length, but the 3rd parameter of length passed in is a negative number: -132967308. That caused the IndexOutOfBoundsException. If I check the GzipDecompressor class of this method in the hadoop, the code will also throw IndexOutoutBoundsException in this case, so this is a RuntimeException case. Why it happened in my test case? Here is my test case: I have a simpel log text file about 700k. I encrypted it with above code using 'AES'. I can encrypted and decrypted to get my original content. The file name is foo.log.crypto, this file extension is registered to invoke this CryptoBasicDecompressor in my testing hadoop using CDH4.1.2 release (hadoop 2.0). Everything works as I expected. The CryptoBasicDecompressor is invoked