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From aaron morton <aa...@thelastpickle.com>
Subject Re: Existing column(s) not readable
Date Tue, 11 Oct 2011 10:46:05 GMT
kewl, 

> * Row is not deleted (other columns can be read, row survives compaction
> with GCGraceSeconds=0)

IIRC row tombstones can hang around for a while (until gc grace has passed), and they only
have an effect on columns that have a lower timstamp. So it's possible to read columns from
a row with a tombstone. 

Can you read the column using a slice range rather than specifying it's name ? 

Aaron

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

On 11/10/2011, at 11:15 PM, Thomas Richter wrote:

> Hi Aaron,
> 
> i invalidated the caches but nothing changed. I didn't get the mentioned
> log line either, but as I read the code SliceByNamesReadCommand uses
> NamesQueryFilter and not SliceQueryFilter.
> 
> Next, there is only one SSTable.
> 
> I can rule out that the row is deleted because I deleted all other rows
> in that CF to reduce data size and speed up testing. I set
> GCGraceSeconds to zero and ran a compaction. All other rows are gone,
> but i can still access at least one column from the left row.
> So as far as I understand it, there should not be a tombstone on row level.
> 
> To make it a list:
> 
> * One SSTable, one row
> *
> * Row is not deleted (other columns can be read, row survives compaction
> with GCGraceSeconds=0)
> * Most columns can be read by get['row']['col'] from cassandra-cli
> * Some columns can not be read by get['row']['col'] from cassandra-cli
> but can be found in output of sstable2json
> * unreadable data survives compaction with GCGraceSeconds=0 (checked
> with sstable2json)
> * Invalidation caches does not help
> * Nothing in the logs
> 
> Does that point into any direction where i should look next?
> 
> Best,
> 
> Thomas
> 
> On 10/11/2011 10:30 AM, aaron morton wrote:
>> Nothing jumps out. The obvious answer is that the column has been deleted. Did you
check all the SSTables ?
>> 
>> It looks like query returned from row cache, otherwise you would see this as well…
>> 
>> DEBUG [ReadStage:34] 2011-10-11 21:11:11,484 SliceQueryFilter.java (line 123) collecting
0 of 2147483647: 1318294191654059:false:354@1318294191654861
>> 
>> Which would mean a version of the column was found. 
>> 
>> If you invalidate the cache with nodetool and run the query and the log message appears
it will mean the column was read from (all of the) sstables. If you do not get a column returned
I would say there is a tombstone in place. It's either a row level or a column level one.
 
>> 
>> Hope that helps. 
>> 
>> -----------------
>> Aaron Morton
>> Freelance Cassandra Developer
>> @aaronmorton
>> http://www.thelastpickle.com
>> 
>> On 11/10/2011, at 10:35 AM, Thomas Richter wrote:
>> 
>>> Hi Aaron,
>>> 
>>> normally we use hector to access cassandra, but for debugging I switched
>>> to cassandra-cli.
>>> 
>>> Column can not be read by a simple
>>> get CFName['rowkey']['colname'];
>>> 
>>> Response is "Value was not found"
>>> if i query another column, everything is just fine.
>>> 
>>> Serverlog for unsuccessful read (keyspace and CF names replaced):
>>> 
>>> DEBUG [pool-1-thread-1] 2011-10-10 23:15:29,739 CassandraServer.java
>>> (line 280) get
>>> 
>>> DEBUG [pool-1-thread-1] 2011-10-10 23:15:29,744 StorageProxy.java (line
>>> 320) Command/ConsistencyLevel is
>>> SliceByNamesReadCommand(table='Keyspace',
>>> key=61636162626139322d396638312d343562382d396637352d393162303337383030393762,
>>> columnParent='QueryPath(columnFamilyName='ColumnFamily',
>>> superColumnName='null', columnName='null')',
>>> columns=[574c303030375030,])/ONE
>>> 
>>> DEBUG [pool-1-thread-1] 2011-10-10 23:15:29,750 ReadCallback.java (line
>>> 86) Blockfor/repair is 1/true; setting up requests to localhost/127.0.0.1
>>> 
>>> DEBUG [pool-1-thread-1] 2011-10-10 23:15:29,750 StorageProxy.java (line
>>> 343) reading data locally
>>> 
>>> DEBUG [ReadStage:33] 2011-10-10 23:15:29,751 StorageProxy.java (line
>>> 448) LocalReadRunnable reading SliceByNamesReadCommand(table='Keyspace',
>>> key=61636162626139322d396638312d343562382d396637352d393162303337383030393762,
>>> columnParent='QueryPath(columnFamilyName='ColumnFamily',
>>> superColumnName='null', columnName='null')', columns=[574c303030375030,])
>>> 
>>> DEBUG [pool-1-thread-1] 2011-10-10 23:15:29,818 StorageProxy.java (line
>>> 393) Read: 67 ms.
>>> 
>>> Log looks fine to me, but no result is returned.
>>> 
>>> Best,
>>> 
>>> Thomas
>>> 
>>> On 10/10/2011 10:00 PM, aaron morton wrote:
>>>> How are they unreadable ? You need to go into some details about what is
going wrong. 
>>>> 
>>>> What sort of read ? 
>>>> What client ? 
>>>> What is in the logging on client and server side ? 
>>>> 
>>>> 
>>>> Try turning the logging up to DEBUG on the server to watch what happens.

>>>> 
>>>> Cheers
>>>> 
>>>> -----------------
>>>> Aaron Morton
>>>> Freelance Cassandra Developer
>>>> @aaronmorton
>>>> http://www.thelastpickle.com
>>>> 
>>>> On 10/10/2011, at 9:23 PM, Thomas Richter wrote:
>>>> 
>>>>> Hi,
>>>>> 
>>>>> no errors in the server logs. The columns are unreadable on all nodes
at
>>>>> any consistency level (ONE, QUORUM, ALL). We started with 0.7.3 and
>>>>> upgraded to 0.7.6-2 two months ago.
>>>>> 
>>>>> Best,
>>>>> 
>>>>> Thomas
>>>>> 
>>>>> On 10/10/2011 10:03 AM, aaron morton wrote:
>>>>>> What error are you seeing  in the server logs ? Are the columns unreadable
at all Consistency Levels ? i.e. are the columns unreadable on all nodes.
>>>>>> 
>>>>>> What is the upgrade history of the cluster ? What version did it
start at ? 
>>>>>> 
>>>>>> Cheers
>>>>>> 
>>>>>> 
>>>>>> -----------------
>>>>>> Aaron Morton
>>>>>> Freelance Cassandra Developer
>>>>>> @aaronmorton
>>>>>> http://www.thelastpickle.com
>>>>>> 
>>>>>> On 10/10/2011, at 7:42 AM, Thomas Richter wrote:
>>>>>> 
>>>>>>> Hi,
>>>>>>> 
>>>>>>> here is some further information. Compaction did not help, but
data is
>>>>>>> still there when I dump the row with sstable2json.
>>>>>>> 
>>>>>>> Best,
>>>>>>> 
>>>>>>> Thomas
>>>>>>> 
>>>>>>> On 10/08/2011 11:30 PM, Thomas Richter wrote:
>>>>>>>> Hi,
>>>>>>>> 
>>>>>>>> we are running a 3 node cassandra (0.7.6-2) cluster and some
of our
>>>>>>>> column families contain quite large rows (400k+ columns,
4-6GB row size).
>>>>>>>> Replicaton factor is 3 for all keyspaces. The cluster is
running fine
>>>>>>>> for several months now and we never experienced any serious
trouble.
>>>>>>>> 
>>>>>>>> Some days ago we noticed, that some previously written columns
could not
>>>>>>>> be read. This does not always happen, and only some dozen
columns out of
>>>>>>>> 400k are affected.
>>>>>>>> 
>>>>>>>> After ruling out application logic as a cause I dumped the
row in
>>>>>>>> question with sstable2json and the columns are there (and
are not marked
>>>>>>>> for deletion).
>>>>>>>> 
>>>>>>>> Next thing was setting up a fresh single node cluster and
copying the
>>>>>>>> column family data to that node. Columns could not be read
either.
>>>>>>>> Right now I'm running a nodetool compact for the cf to see
if data could
>>>>>>>> be read afterwards.
>>>>>>>> 
>>>>>>>> Is there any explanation for such behavior? Are there any
suggestions
>>>>>>>> for further investigation?
>>>>>>>> 
>>>>>>>> TIA,
>>>>>>>> 
>>>>>>>> Thomas
>>>>>>> 
>>>>>> 
>>>>> 
>>>> 
>>> 
>> 
> 


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