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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Leveled Compaction in cassandra1.0 may not be perfect
Date Sun, 04 Dec 2011 23:47:27 GMT
On Fri, Dec 2, 2011 at 8:13 PM, liangfeng <liangfeng@made-in-china.com> wrote:
> 1.There is no implementation in cassandra1.0 to ensure the conclusion "Only
> enough space for 10x the sstable size needs to be reserved for temporary use by
> compaction",so one special compaction may need big free disk space all the same.
> 2.Leveled compaction *will* do too much i/o,especially when we use
> RandomPartitioner(because md5 token will cause overlap of many sstables all the
> time).
> These two points may cause uncontrollablity when compaction occurs.

We specifically create non-overlapping, fixed-size sstables so that
there is no such thing as a "special" or unusually large compaction.
(All sstables are sorted by row key in token order, so partitioner
choice has no effect here.)

You should look at the org.apache.cassandra.db.compaction package and
read the original leveldb implementation notes at
http://leveldb.googlecode.com/svn/trunk/doc/impl.html for more
details.

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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