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http://issues.apache.org/jira/browse/HADOOP-54?page=comments#action_12423414 ]
Owen O'Malley commented on HADOOP-54:
-------------------------------------
Sorry for being dense. I missed the fact that you wanted to preserve key-value
pair compression as an option.
I'd propose spliting the classes like:
SequenceFile.Writer // uncompressed
SequenceFile.RecordCompressWriter extends Writer
SequenceFile.BlockCompressWriter extends Writer
They would have the current interface, with the following new functions:
void append(byte[] key, int keyOffset, int keyLength, byte[] value, int
valueOffset, int valueLength);
boolean canAppendCompressed();
void appendCompressed(byte[] key, int keyOffset, int keyLength,
byte[] value, int valueOffset,
int valueLength);
when we add custom compressors, we can add the compressor to the constructors.
The Reader should have methods like:
boolean next(DataOutputStream key, DataOutputStream value);
boolean canReadCompressed();
void readCompressed(DataOutputStream key, DataOutputStream value);
when we add custom compressors, we can add a getter for them like:
StreamCompressor getCompressor();
As an implementation, I'd consider having SequenceFile.Reader be a bridge to
the class that is doing the reading based on the how it is compressed.
Thoughts?
> SequenceFile should compress blocks, not individual entries
> -----------------------------------------------------------
>
> Key: HADOOP-54
> URL: http://issues.apache.org/jira/browse/HADOOP-54
> Project: Hadoop
> Issue Type: Improvement
> Components: io
> Affects Versions: 0.2.0
> Reporter: Doug Cutting
> Assigned To: Arun C Murthy
> Fix For: 0.5.0
>
> Attachments: VIntCompressionResults.txt
>
>
> SequenceFile will optionally compress individual values. But both
> compression and performance would be much better if sequences of keys and
> values are compressed together. Sync marks should only be placed between
> blocks. This will require some changes to MapFile too, so that all file
> positions stored there are the positions of blocks, not entries within
> blocks. Probably this can be accomplished by adding a
> getBlockStartPosition() method to SequenceFile.Writer.
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