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From aaron morton <aa...@thelastpickle.com>
Subject Re: Nodes not picking up data on repair, disk loaded unevenly
Date Wed, 06 Jun 2012 09:23:39 GMT
You are basically in trouble. If you can nuke it and start again it would be easier. If you
want to figure out how to get out of it keep the cluster up and have a play. 


> -What I think the solution should be:
You want to get repair to work before you start deleting data. 

> At ~840GB I'm probably running close
> to the max load I should have on a node,
roughly 300GB to 400GB is the max load

> On node #1 I was able to successfully run a scrub and
> major compaction, 
In this situation running a major compaction is now what you want. it creates a huge file
that can only be compacted if there is enough space for another huge file. Smaller files only
need small space to be compacted. 

> Is there something I should be looking for in the logs to verify that the
> repair was successful? 
grep for "repair command"

The shortcut on EC2 is add an EBS volumn, tell cassandra it can store stuff there (in the
yaml) and buy some breathing room. 


What version are you using ?

Has there been times when nodes were down ? 

Clear as much space as possible from the disk. Check for snapshots in all KS's. 

What KS's (including the system KS) are taking up the most space ? Are there a lot of hints
in the system KS (they are not replicated)?

Try to get a feel for what CF's are taking up the space or not as the case my be. Look in
nodetool cfstats to see how big the rows are. 

I you have enabled compression run nodetool upgradetables to compress them. 


In general, try to get free space on the nodes by using compaction, moving files to a new
mount etc so that you can get repair to run. 

Cheers

 

-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 6/06/2012, at 6:53 AM, Luke Hospadaruk wrote:

> I have a 4-node cluster with one keyspace (aside from the system keyspace)
> with the replication factor set to 4.  The disk usage between the nodes is
> pretty wildly different and I'm wondering why.  It's becoming a problem
> because one node is getting to the point where it sometimes fails to
> compact because it doesn't have enough space.
> 
> I've been doing a lot of experimenting with the schema, adding/dropping
> things, changing settings around (not ideal I realize, but we're still in
> development).
> 
> In an ideal world, I'd launch another cluster (this is all hosted in
> amazon), copy all the data to that, and just get rid of my current
> cluster, but the current cluster is in use by some other parties so
> rebuilding everything is impractical (although possible if it's the only
> reliable solution).
> 
> $ nodetool -h localhost ring
> Address     DC        Rack  Status State  Load       Owns   Token
> 
> 
> 1.xx.xx.xx   Cassandra   rack1       Up     Normal  837.8 GB   25.00%  0
> 
> 2.xx.xx.xx   Cassandra   rack1       Up     Normal  1.17 TB    25.00%
> 42535295865117307932921825928971026432
> 3.xx.xx.xx   Cassandra   rack1       Up     Normal  977.23 GB  25.00%
> 85070591730234615865843651857942052864
> 4.xx.xx.xx   Cassandra   rack1       Up     Normal  291.2 GB   25.00%
> 127605887595351923798765477786913079296
> 
> -Problems I'm having:
> Nodes are running out of space and are apparently unable to perform
> compactions because of it.  These machines have 1.7T total space each.
> 
> The logs for node #2 have a lot of warnings about insufficient space for
> compaction.  Node number 4 was so extremely out of space (cassandra was
> failing to start because of it)that I removed all the SSTables for one of
> the less essential column families just to bring it back online.
> 
> 
> I have (since I started noticing these issues) enabled compression for all
> my column families.  On node #1 I was able to successfully run a scrub and
> major compaction, so I suspect that the disk usage for node #1 is about
> where all the other nodes should be.  At ~840GB I'm probably running close
> to the max load I should have on a node, so I may need to launch more
> nodes into the cluster, but I'd like to get things straightened out before
> I introduce more potential issues (token moving, etc).
> 
> Node #4 seems not to be picking up all the data it should have (since
> repication factor == number of nodes, the load should be roughly the
> same?).  I've run repairs on that node to seemingly no avail (after repair
> finishes, it still has about the same disk usage, which is much too low).
> 
> 
> -What I think the solution should be:
> One node at a time:
> 1) nodetool drain the node
> 2) shut down cassandra on the node
> 3) wipe out all the data in my keyspace on the node
> 4) bring cassandra back up
> 5) nodetool repair
> 
> -My concern:
> This is basically what I did with node #4 (although I didn't drain, and I
> didn't wipe the entire keyspace), and it doesn't seem to have regained all
> the data it's supposed to have after the repair. The column family should
> have at least 200-300GB of data, and the SSTables in the data directory
> only total about 11GB, am I missing something?
> 
> Is there a way to verify that a node _really_ has all the data it's
> supposed to have?
> 
> I don't want to do this process to each node and discover at the end of it
> that I've lost a ton of data.
> 
> Is there something I should be looking for in the logs to verify that the
> repair was successful?  If I do a 'nodetool netstats' during the repair I
> don't see any streams going in or out of node #4.
> 
> Thanks,
> Luke
> 


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