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From Daning <dan...@netseer.com>
Subject Re: Weird problem with empty CF
Date Tue, 04 Oct 2011 17:03:51 GMT
Thanks Aaron.  How about I set the gc_grace_seconds to 0 or like 2 
hours? I like to clean up tomebstone sooner, I don't care losing some 
data and all my columns have ttl.

If one node is down longer than gc_grace_seconds, and I got tombstone 
removed, once the node is up, from my understanding deleted data will be 
synced back. In this case my data will be processed twice and it will 
not be a big deal to me.

Thanks,

Daning


On 10/04/2011 01:27 AM, aaron morton wrote:
> Yes that's the slice query skipping past the tombstone columns.
>
> Cheers
>
> -----------------
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 4/10/2011, at 4:24 PM, Daning Wang wrote:
>
>> Lots of SliceQueryFilter in the log, is that handling tombstone?
>>
>> DEBUG [ReadStage:49] 2011-10-03 20:15:07,942 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317582939743663:true:4@1317582939933000
>> DEBUG [ReadStage:50] 2011-10-03 20:15:07,942 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317573253148778:true:4@1317573253354000
>> DEBUG [ReadStage:43] 2011-10-03 20:15:07,942 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317669552951428:true:4@1317669553018000
>> DEBUG [ReadStage:33] 2011-10-03 20:15:07,942 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317581886709261:true:4@1317581886957000
>> DEBUG [ReadStage:52] 2011-10-03 20:15:07,942 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317568165152246:true:4@1317568165482000
>> DEBUG [ReadStage:36] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317567265089211:true:4@1317567265405000
>> DEBUG [ReadStage:53] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317674324843122:true:4@1317674324946000
>> DEBUG [ReadStage:38] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317571990078721:true:4@1317571990141000
>> DEBUG [ReadStage:57] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317671855234221:true:4@1317671855239000
>> DEBUG [ReadStage:54] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317558305262954:true:4@1317558305337000
>> DEBUG [RequestResponseStage:11] 2011-10-03 20:15:07,941 
>> ResponseVerbHandler.java (line 48) Processing response on a callback 
>> from 12347@/10.210.101.104 <http://10.210.101.104/>
>> DEBUG [RequestResponseStage:9] 2011-10-03 20:15:07,941 
>> AbstractRowResolver.java (line 66) Preprocessed data response
>> DEBUG [RequestResponseStage:13] 2011-10-03 20:15:07,941 
>> AbstractRowResolver.java (line 66) Preprocessed digest response
>> DEBUG [ReadStage:58] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317581337972739:true:4@1317581338044000
>> DEBUG [ReadStage:64] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317582656796332:true:4@1317582656970000
>> DEBUG [ReadStage:55] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317569432886284:true:4@1317569432984000
>> DEBUG [ReadStage:45] 2011-10-03 20:15:07,941 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317572658687019:true:4@1317572658718000
>> DEBUG [ReadStage:47] 2011-10-03 20:15:07,940 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317582281617755:true:4@1317582281717000
>> DEBUG [ReadStage:48] 2011-10-03 20:15:07,940 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1: 1317549607869226:true:4@1317549608118000
>> DEBUG [ReadStage:34] 2011-10-03 20:15:07,940 SliceQueryFilter.java 
>> (line 123) collecting 0 of 1:
>> On Thu, Sep 29, 2011 at 2:17 PM, aaron morton 
>> <aaron@thelastpickle.com <mailto:aaron@thelastpickle.com>> wrote:
>>
>>     As with any situation involving the un-dead, it really is the
>>     number of Zombies, Mummies or Vampires that is the concern.
>>
>>     If you delete data there will always be tombstones. If you have a
>>     delete heavy workload there will be more tombstones. This is why
>>     implementing a queue with cassandra is a bad idea.
>>
>>     gc_grace_seconds (and column TTL) are the *minimum* about of time
>>     the tombstones will stay in the data files, there is no maximum.
>>
>>     Your read performance also depends on the number of SSTables the
>>     row is spread over, see
>>     http://thelastpickle.com/2011/04/28/Forces-of-Write-and-Read/
>>
>>     If you really wanted to purge them then yes a repair and then
>>     major compaction would be the way to go. Also consider if it's
>>     possible to design the data model around the problem, e.g.
>>     partitioning rows by date. IMHO I would look to make data model
>>     changes before implementing a compaction policy, or consider if
>>     cassandra is the right store if you have a delete heavy workload.
>>
>>     Cheers
>>
>>
>>     -----------------
>>     Aaron Morton
>>     Freelance Cassandra Developer
>>     @aaronmorton
>>     http://www.thelastpickle.com <http://www.thelastpickle.com/>
>>
>>     On 30/09/2011, at 3:27 AM, Daning Wang wrote:
>>
>>>     Jonathan/Aaron,
>>>
>>>     Thank you guy's reply, I will change GCGracePeriod to 1 day to
>>>     see what will happen.
>>>
>>>     Is there a way to purge tombstones at anytime? because if
>>>     tombstones affect performance, we want them to be purged right
>>>     away, not after GCGracePeriod. We know all the nodes are up, and
>>>     we can do repair first to make sure the consistency before purging.
>>>
>>>     Thanks,
>>>
>>>     Daning
>>>
>>>
>>>     On Wed, Sep 28, 2011 at 5:22 PM, aaron morton
>>>     <aaron@thelastpickle.com <mailto:aaron@thelastpickle.com>> wrote:
>>>
>>>         if I had to guess I would say it was spending time handling
>>>         tombstones. If you see it happen again, and are interested,
>>>         turn the logging up to DEBUG and look for messages from
>>>         something starting with "Slice"
>>>
>>>         Minor (automatic) compaction will, over time, purge the
>>>         tombstones. Until then reads must read discard the data
>>>         deleted by the tombstones. If you perform a big (i.e. 100k's
>>>         ) delete this can reduce performance until compaction does
>>>         it's thing.
>>>
>>>         My second guess would be read repair (or the simple
>>>         consistency checks on read) kicking in. That would show up
>>>         in the "ReadRepairStage" in TPSTATS
>>>
>>>         it may have been neither of those two things, just guesses.
>>>         If you have more issues let us know and provide some more info.
>>>
>>>         Cheers
>>>
>>>
>>>         -----------------
>>>         Aaron Morton
>>>         Freelance Cassandra Developer
>>>         @aaronmorton
>>>         http://www.thelastpickle.com <http://www.thelastpickle.com/>
>>>
>>>         On 29/09/2011, at 6:35 AM, Daning wrote:
>>>
>>>         > I have an app polling a few CFs (select first N * from
>>>         CF), there were data in CFs but later were deleted so CFs
>>>         were empty for a long time. I found Cassandra CPU usage was
>>>         getting high to 80%, normally it uses less than 30%. I
>>>         issued the select query manually and feel the response is
>>>         slow. I have tried nodetool compact/repair for those CFs but
>>>         that does not work. later, I issue 'truncate' for all the
>>>         CFs and CPU usage gets down to 1%.
>>>         >
>>>         > Can somebody explain to me why I need to truncate an empty
>>>         CF? and what else I could do to bring the CPU usage down?
>>>         >
>>>         > I am running 0.8.6.
>>>         >
>>>         > Thanks,
>>>         >
>>>         > Daning
>>>         >
>>>
>>>
>>
>>
>


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