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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Massive writes when only reading from Cassandra
Date Sat, 10 Sep 2011 21:24:10 GMT
Two possibilities:

1) Hinted handoff (this will show up in the logs on the sending
machine, on the receiving one it will just look like any other write)

2) You have something doing writes that you're not aware of, I guess
you could track that down using wireshark to see where the write
messages are coming from

On Sat, Sep 10, 2011 at 3:56 PM, Jeremy Hanna
<jeremy.hanna1234@gmail.com> wrote:
> Oh and we're running 0.8.4 and the RF is 3.
>
> On Sep 10, 2011, at 3:49 PM, Jeremy Hanna wrote:
>
>> In addition, the mutation stage and the read stage are backed up like:
>>
>> Pool Name                    Active   Pending   Blocked
>> ReadStage                        32       773         0
>> RequestResponseStage              0         0         0
>> ReadRepairStage                   0         0         0
>> MutationStage                   158    525918         0
>> ReplicateOnWriteStage             0         0         0
>> GossipStage                       0         0         0
>> AntiEntropyStage                  0         0         0
>> MigrationStage                    0         0         0
>> StreamStage                       0         0         0
>> MemtablePostFlusher               1         5         0
>> FILEUTILS-DELETE-POOL             0         0         0
>> FlushWriter                       2         5         0
>> MiscStage                         0         0         0
>> FlushSorter                       0         0         0
>> InternalResponseStage             0         0         0
>> HintedHandoff                     0         0         0
>> CompactionManager               n/a        29
>> MessagingService                n/a      0,34
>>
>> On Sep 10, 2011, at 3:38 PM, Jeremy Hanna wrote:
>>
>>> We are experiencing massive writes to column families when only doing reads from
Cassandra.  A set of 5 hadoop jobs are reading from Cassandra and then writing out to hdfs.
 That is the only thing operating on the cluster.  We are reading at CL.QUORUM with hadoop
and have written with CL.QUORUM.  Read repair chance is set to 0.0 on all column families.
 However, in the logs, I'm seeing flush after flush of memtables and compactions taking place.
 Is there something else that would be writing based on the above description?
>>>
>>> Jeremy
>>
>
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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