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From Sylvain Lebresne <sylv...@datastax.com>
Subject Re: Meaning of compression chunk_length_kb
Date Thu, 14 Jun 2012 12:52:46 GMT
> It means that uncompressed sstable data is compressed to approximately
> chunk_length_kb and every read needs to read approximately chunk_length_kb and
> decompress it to read any value from compressed range  ?
>
> Or it means approximately chunk_length_kb of sstable data is compressed and
> stored on disk, so similar values must be in chunk_length_kb range to make
> compression efficient  ?

Pretty much the second one. We compress the sstable data by blocks of
chunk_length_kb (so chunk_length_kb of uncompressed data), yelding a number
of compressed blocks that are hopefully smaller than that. It does mean however
that every read needs to read and deserialize a full (compressed) block and
decompress it to fetch any value within this block.

Sylvain

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