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From Daning <dan...@netseer.com>
Subject Re: Weird problem with empty CF
Date Wed, 05 Oct 2011 00:18:39 GMT
Thanks.  Do you have plan to improve this? I think tombstone should be 
separated with live data since it serves different purpose, built in 
separate SSTable or indexed differently. It is pretty costly to do 
filtering while reading.

Daning

On 10/04/2011 01:34 PM, aaron morton wrote:
> I would not get gc_grace seconds to 0, set to to something small.
>
> gc_grace_seconds or ttl is only the minimum amount of time the column 
> will stay in the data files. The columns are only purged when 
> compaction runs some time after that timespan has ended.
>
> If you are seeing issues where a heavy delete workload is having an 
> noticeably adverse effect on read performance then you should look at 
> the data model. Consider ways to spread the write / read / delete 
> workload over multiple rows.
>
> If you cannot get away from it then experiment with reducing the 
> min_compactioon_threshold of the CF's so that compaction kicks in 
> quicker, and (potentially) tombstones are purged faster.
>
> Chees
>
>
> -----------------
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 5/10/2011, at 6:03 AM, Daning wrote:
>
>> 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 <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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