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From Mike <>
Subject Size Tiered -> Leveled Compaction
Date Wed, 13 Feb 2013 15:50:05 GMT

I'm investigating the transition of some of our column families from 
Size Tiered -> Leveled Compaction.  I believe we have some 
high-read-load column families that would benefit tremendously.

I've stood up a test DB Node to investigate the transition.  I 
successfully alter the column family, and I immediately noticed a large 
number (1000+) pending compaction tasks become available, but no 
compaction get executed.

I tried running "nodetool sstableupgrade" on the column family, and the 
compaction tasks don't move.

I also notice no changes to the size and distribution of the existing 

I then run a major compaction on the column family.  All pending 
compaction tasks get run, and the SSTables have a distribution that I 
would expect from LeveledCompaction (lots and lots of 10MB files).

Couple of questions:

1) Is a major compaction required to transition from size-tiered to 
leveled compaction?
2) Are major compactions as much of a concern for LeveledCompaction as 
their are for Size Tiered?

All the documentation I found concerning transitioning from Size Tiered 
to Level compaction discuss the alter table cql command, but I haven't 
found too much on what else needs to be done after the schema change.

I did these tests with Cassandra 1.1.9.


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