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From liangfeng <liangf...@made-in-china.com>
Subject Re: Leveled Compaction in cassandra1.0 may not be perfect
Date Sat, 03 Dec 2011 02:13:30 GMT


Jonathan Ellis <jbellis <at> gmail.com> writes:

> 
> 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.
> 

Yes.In fact ,I want to put two points in this topic.
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.
                             Thanks!





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