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[Greg Bone]

Re: high pending compactions

[Greg Bone]

I'm looking into creation of monitoring thresholds for cassandra to report
on its health. Does it make sense to set an alert threshold on compaction
stats? If so, would setting it to a value equal to or greater than
concurrent compactions make sense?

Thanks,
Greg




On Mon, Jun 9, 2014 at 2:14 PM, S C as...@outlook.com wrote:

 Thank you all for quick responses.
 --
 From: clohf...@blackbirdit.com
 Subject: Re: high pending compactions
 Date: Mon, 9 Jun 2014 14:11:36 -0500
 To: user@cassandra.apache.org

 Bean: org.apache.cassandra.db.CompactionManager

 also nodetool compactionstats gives you how many are in the queue +
 estimate of how many will be needed.

 in 1.1 you will OOM *far* before you hit the limit,.  In theory though,
 the compaction executor is a little special cased and will actually throw
 an exception (normally it will block)

 Chris

 On Jun 9, 2014, at 7:49 AM, S C as...@outlook.com wrote:

 Thank you all for valuable suggestions. Couple more questions,

 How to check the compaction queue? MBean/C* system log ?
 What happens if the queue is full?

 --
 From: colinkuo...@gmail.com
 Date: Mon, 9 Jun 2014 18:53:41 +0800
 Subject: Re: high pending compactions
 To: user@cassandra.apache.org

 As Jake suggested, you could firstly increase
 compaction_throughput_mb_per_sec and concurrent_compactions to suitable
 values if system resource is allowed. From my understanding, major
 compaction will internally acquire lock before running compaction. In your
 case, there might be a major compaction blocking the pending following
 compaction tasks. You could check the result of nodetool compactionstats
 and C* system log for double confirm.

 If the running compaction is compacting wide row for a long time, you
 could try to tune in_memory_compaction_limit_in_mb value.

 Thanks,



 On Sun, Jun 8, 2014 at 11:27 PM, S C as...@outlook.com wrote:

 I am using Cassandra 1.1 (sorry bit old) and I am seeing high pending
 compaction count. pending tasks: 67 while active compaction tasks are
 not more than 5. I have a 24CPU machine. Shouldn't I be seeing more
 compactions? Is this a pattern of high writes and compactions backing up?
 How can I improve this? Here are my thoughts.


1. Increase memtable_total_space_in_mb
2. Increase compaction_throughput_mb_per_sec
3. Increase concurrent_compactions


 Sorry if this was discussed already. Any pointers is much appreciated.

 Thanks,
 Kumar

Re: Auto-Bootstrap not Auto-Bootstrapping?

[Greg Bone]

If seed nodes do not auto bootstrap, what is the procedure for replacing a node 
in a three node cluster, with all of them identified as seed nodes?

Here's what I am thinking:
1) Add a 4th node to the cluster which is not a seed node
2) Decommission one of the seed nodes when data
 finished streaming to new node
3) convert newly added 4th node to a seed node by 
updating the cassandra.yaml file.
Keith Wright kwright at nanigans.com writes: