I think you're confusing "temporary space used during a compaction operation" with "total i/o done by compaction."
Leveled compaction *will* do more i/o than size-tiered, because it's enforcing tighter guarantees on how compacted the data is. On Fri, Dec 2, 2011 at 1:01 AM, liangfeng <liangf...@made-in-china.com> wrote: > Hello，everyone! > In this > doc(http://www.datastax.com/dev/blog/leveled-compaction-in-apache-cassandra),I > found a conclusion "Only enough space for 10x the sstable size needs to be > reserved for temporary use by compaction".I don't know how can we got this > conclusion,but I guess the author of this doc may got this conclusion by one > compaction rule from levelDB.In one doc of > levelDB(http://leveldb.googlecode.com/svn/trunk/doc/impl.html),I found this > rule > "We also switch to a new output file when the key range of the current output > file has grown enough to overlap more then ten level-(L+2) files".As this > compaction rule descripting,10x the sstable size is enough for every > compaction.Unfortunatly,cassandra1.0 may not implement this compaction > rule,so I > think this conclusion may be arbitrary.Everyone,what do you think about it? > Of course，implement this compaction rule may not be hard,but this > implementation may cause another problem.Many small sstables which overlap > just > 10 sstables with next level may be generated in compaction,especially when we > use RandomPartitioner.This may cause many compactions when these small > sstables > have to uplevel to next level.In my practice,I write 120g data to one > cassandra > node,and cassandra node spent 24 hourse to compacte this data by Leveled > Compaction.So,I don't think Leveled Compaction is perfect.What do you think > about it,my friends? > -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
