Edward, you make a good point, and I do think am getting closer to having to increase my cluster size (I'm around ~300GB/node now).  

In my case, I think it was neither.  I had one node OOM after working on a large compaction but it continued to run in a zombie like state (constantly GC'ing), which I didn't have an alert on.  Then I had the bad luck of a "close token" also starting a large compaction.  I have RF=3 with some of my R/W patterns at quorum, causing that segment of my cluster to get slow (e.g. a % of of my traffic started to slow).  I was running 1.1.2 (I haven't had to poke anything for quite some time, obviously), so I upgraded before moving on (as I saw a lot of bug fixes to compaction issues in release notes).  But the upgrade caused even more nodes to start compactions.  Which lead to my original email... I had a cluster where 80% of my nodes were compacting, and I really needed to boost production traffic and couldn't seem to "tamp cassandra down" temporarily.  

Thanks for the advice everyone!


On Tue, Apr 2, 2013 at 10:20 AM, Edward Capriolo <edlinuxguru@gmail.com> wrote:
Settings do not make compactions go away. If your compactions are "out of control" it usually means one of these things,
1)  you have a corrupt table that the compaction never finishes on, sstables count keep growing
2) you do not have enough hardware to handle your write load

On Tue, Apr 2, 2013 at 7:50 AM, William Oberman <oberman@civicscience.com> wrote:
Thanks Gregg & Aaron. Missed that setting! 

On Tuesday, April 2, 2013, aaron morton wrote:
Set the min and max 
compaction thresholds for a given column family
+1 for setting the max_compaction_threshold (as well as the min) on the a CF when you are getting behind. It can limit the size of the compactions and give things a chance to complete in a reasonable time. 


Aaron Morton
Freelance Cassandra Consultant
New Zealand


On 2/04/2013, at 3:42 AM, Gregg Ulrich <gulrich@netflix.com> wrote:

You may want to set compaction threshold and not throughput.  If you set the min threshold to something very large (100000), compactions will not start until cassandra finds this many files to compact (which it should not).

In the past I have used this to stop compactions on a node, and then run an offline major compaction to get though the compaction, then set the min threshold back.  Not everyone likes major compactions though.

  setcompactionthreshold <keyspace> <cfname> <minthreshold> <maxthreshold> - Set the min and max 
compaction thresholds for a given column family

On Mon, Apr 1, 2013 at 12:38 PM, William Oberman <oberman@civicscience.com> wrote:
I'll skip the prelude, but I worked myself into a bit of a jam.  I'm recovering now, but I want to double check if I'm thinking about things correct.

Basically, I was in a state where a majority of my servers wanted to do compactions, and rather large ones.  This was impacting my site performance.  I tried nodetool stop COMPACTION.  I tried setcompactionthroughput=1.  I tried restarting servers, but they'd restart the compactions pretty much immediately on boot.

Then I realized that:
nodetool stop COMPACTION
only stopped running compactions, and then the compactions would re-enqueue themselves rather quickly.

So, right now I have:
1.) scripts running on N-1 servers looping on "nodetool stop COMPACTION" in a tight loop
2.) On the "Nth" server I've disabled gossip/thrift and turned up setcompactionthroughput to 999
3.) When the Nth server completes, I pick from the remaining N-1 (well, I'm still running the first compaction, which is going to take 12 more hours, but that is the plan at least).

Does this make sense?  Other than the fact there was probably warning signs that would have prevented me from getting into this state in the first place? :-)


Will Oberman
Civic Science, Inc.
6101 Penn Avenue, Fifth Floor
Pittsburgh, PA 15206
(M) 412-480-7835
(E) oberman@civicscience.com