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From Erik Forkalsud <eforkals...@cj.com>
Subject Re: best way to clean up a column family? 60Gig of dangling data
Date Fri, 01 Mar 2013 00:55:55 GMT

Have you tried to (via jmx) call 
org.apache.cassandra.db.CompactionManager.forceUserDefinedCompaction() 
and give it the name of your SSTable file.

It's a trick I use to aggressively get rid of expired data, i.e. if I 
have a column family where all data is written with a TTL of 30 days, 
any SSTable files with last modified time of more than 30 days ago will 
have only expired data, so I call the above function to compact those 
files one by one.  In your case it sounds like it's not expired data, 
but data that belongs on other nodes that you want to get rid of.  I'm 
not sure if compaction will drop data that doesn't fall within the nodes 
key range, but if it does this method should have the effect you're after.


- Erik -


On 02/27/2013 08:51 PM, Hiller, Dean wrote:
> Okay, we had 6 nodes of 130Gig and it was slowly increasing.  Through our operations
to modify bloomfilter fp chance, we screwed something up as trying to relieve memory pressures
was tough.  Anyways, somehow, this caused nodes 1, 2, and 3 to jump to around 200Gig and our
incoming data stream is completely constant at around 260 points/second.
>
> Sooo, we know this dangling data(around 60Gigs) is in one single column family.  Node
1, 2, and 3 is for the first token range according to ringdescribe.  It is almost like the
issue is now replicated to the other two nodes.  Is there any way we can go about debugging
this and release the 60 gigs of disk space?
>
> Also, the upgradesstables when memory is already close to max is not working too well.
 Can we do this instead(ie. Is it safe?)?
>
>   1.  Bring down the node
>   2.  Move all the *Index.db files to another directory
>   3.  Start the node and run upgradesstables
>
> We know this relieves a ton of memory out of the gate for us.  We are trying to get memory
back down by a gig, then upgrade to 1.2.2 and switch to leveled compaction as we have ZERO
I/o really going on most of the time and really just have this bad bad memory bottleneck(iostat
shows nothing typically as we are bottlenecked by memory).
>
> Thanks,
> Dean


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