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From "Dan Hendry" <>
Subject Cassandra 1.0.0 - Node Load Bug
Date Thu, 20 Oct 2011 16:53:09 GMT
I have been playing around with Cassandra 1.0.0 in our test environment it
seems pretty sweet so far. I have however come across what appears to be a
bug tracking node load. I have enabled compression and levelled compaction
on all CFs (scrub  + snapshot deletion) and the nodes have been operating
normally for a day or two. I started getting concerned when the load as
reported by nodetool ring kept increasing (it seems monotonically) despite
seeing a compression ratio of ~2.5x (as a side note, I find it strange
Cassandra does not provide the compression ratio via jmx or in the logs). I
initially thought there might be a bug in cleaning up obsolete SSTables but
I then noticed the following discrepancy:


Nodetool ring reports:

          datacenter1 rack1       Up     Normal  8.64
GB         50.00%  170141183460469231731687303715884105727


Yet du . -h reports: only 2.4G in the data directory.


After restarting the node, nodetool ring reports a more accurate:    datacenter1 rack1       Up     Normal  2.35 GB
50.00%  170141183460469231731687303715884105727


Again, both compression and levelled compaction have been enabled on all
CFs. Is this a known issue or has anybody else observed a similar pattern?


Dan Hendry

(403) 660-2297


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