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?
