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From Shubham Jaju <shub...@vassarlabs.com>
Subject Re: Issue with Cassandra consistency in results
Date Wed, 22 Mar 2017 01:57:38 GMT
Hi

This issue used to appear with me . What I figured in my case was
  1. I had 3 machines
  2. Inserted the data with ONE consistency (i.e there is no guarantee that
data was propagated to remaining nodes , cassandra is supposed to take care
of that).
  3. Later I figured also that one of machines has different hard disk
space compared to other two (less and data size was more ) . i.e it was not
able to contain whole set of data.

So I think in above cases ( 2,3 )if you will query you will get different
results as nodes are not in sync.
nodetool repair should solve this problem. But it takes more time if you
have more data.
Check if this solves you problem.

Regards

Shubham Jaju

On Wed, Mar 22, 2017 at 12:23 AM, srinivasarao daruna <
sree.srinu38@gmail.com> wrote:

> The same issue is appearing in CQL Shell as well.
>
> 1) Entered into cqlsh
> 2) SET CONSISTENCY QUORUM;
> 3) Ran a select * with partition key in where cluase.
>
> First result gave 0 records,
> and Next records gave results.
>
> Its really freaking out us at the moment. And nothing in debug.log or
> system.log.
>
> Thank You,
> Regards,
> Srini
>
> On Fri, Mar 17, 2017 at 2:33 AM, daemeon reiydelle <daemeonr@gmail.com>
> wrote:
>
>> The prep is needed. If I recall correctly it must remain in cache for the
>> query to complete. I don't have the docs to dig out the yaml parm to adjust
>> query cache. I had run into the problem stress testing a smallish cluster
>> with many queries at once.
>>
>> Do you have a sense of how many distinct queries are hitting the cluster
>> at peak?
>>
>> If many clients, how do you balance the connection load or do you always
>> hit the same node?
>>
>>
>> sent from my mobile
>> Daemeon Reiydelle
>> skype daemeon.c.m.reiydelle
>> USA 415.501.0198
>>
>> On Mar 16, 2017 3:25 PM, "srinivasarao daruna" <sree.srinu38@gmail.com>
>> wrote:
>>
>>> Hi reiydelle,
>>>
>>> I cannot confirm the range as the volume of data is huge and the query
>>> frequency is also high.
>>> If the cache is the cause of issue, can we increase cache size or is
>>> there solution to avoid dropped prep statements.?
>>>
>>>
>>>
>>>
>>>
>>>
>>> Thank You,
>>> Regards,
>>> Srini
>>>
>>> On Thu, Mar 16, 2017 at 2:13 PM, daemeon reiydelle <daemeonr@gmail.com>
>>> wrote:
>>>
>>>> The discard due to oom is causing the zero returned. I would guess a
>>>> cache miss problem of some sort, but not sure. Are you using row, index,
>>>> etc. caches? Are you seeing the failed prep statement on random nodes (duh,
>>>> nodes that have the relevant data ranges)?
>>>>
>>>>
>>>> *.......*
>>>>
>>>>
>>>>
>>>> *Daemeon C.M. ReiydelleUSA (+1) 415.501.0198 <+1%20415-501-0198>London
>>>> (+44) (0) 20 8144 9872 <+44%2020%208144%209872>*
>>>>
>>>> On Thu, Mar 16, 2017 at 10:56 AM, Ryan Svihla <rs@foundev.pro> wrote:
>>>>
>>>>> Depends actually, restore just restores what's there, so if only one
>>>>> node had a copy of the data then only one node had a copy of the data
>>>>> meaning quorum will still be wrong sometimes.
>>>>>
>>>>> On Thu, Mar 16, 2017 at 1:53 PM, Arvydas Jonusonis <
>>>>> arvydas.jonusonis@gmail.com> wrote:
>>>>>
>>>>>> If the data was written at ONE, consistency is not guaranteed. ..but
>>>>>> considering you just restored the cluster, there's a good chance
something
>>>>>> else is off.
>>>>>>
>>>>>> On Thu, Mar 16, 2017 at 18:19 srinivasarao daruna <
>>>>>> sree.srinu38@gmail.com> wrote:
>>>>>>
>>>>>>> Want to make read and write QUORUM as well.
>>>>>>>
>>>>>>>
>>>>>>> On Mar 16, 2017 1:09 PM, "Ryan Svihla" <rs@foundev.pro>
wrote:
>>>>>>>
>>>>>>>         Replication factor is 3, and write consistency is ONE
and
>>>>>>> read consistency is QUORUM.
>>>>>>>
>>>>>>> That combination is not gonna work well:
>>>>>>>
>>>>>>> *Write succeeds to NODE A but fails on node B,C*
>>>>>>>
>>>>>>> *Read goes to NODE B, C*
>>>>>>>
>>>>>>> If you can tolerate some temporary inaccuracy you can use QUORUM
but
>>>>>>> may still have the situation where
>>>>>>>
>>>>>>> Write succeeds on node A a timestamp 1, B succeeds at timestamp
2
>>>>>>> Read succeeds on node B and C at timestamp 1
>>>>>>>
>>>>>>> If you need fully race condition free counts I'm afraid you need
to
>>>>>>> use SERIAL or LOCAL_SERIAL (for in DC only accuracy)
>>>>>>>
>>>>>>> On Thu, Mar 16, 2017 at 1:04 PM, srinivasarao daruna <
>>>>>>> sree.srinu38@gmail.com> wrote:
>>>>>>>
>>>>>>> Replication strategy is SimpleReplicationStrategy.
>>>>>>>
>>>>>>> Smith is : EC2 snitch. As we deployed cluster on EC2 instances.
>>>>>>>
>>>>>>> I was worried that CL=ALL have more read latency and read failures.
>>>>>>> But won't rule out trying it.
>>>>>>>
>>>>>>> Should I switch select count (*) to select partition_key column?
>>>>>>> Would that be of any help.?
>>>>>>>
>>>>>>>
>>>>>>> Thank you
>>>>>>> Regards
>>>>>>> Srini
>>>>>>>
>>>>>>> On Mar 16, 2017 12:46 PM, "Arvydas Jonusonis" <
>>>>>>> arvydas.jonusonis@gmail.com> wrote:
>>>>>>>
>>>>>>> What are your replication strategy and snitch settings?
>>>>>>>
>>>>>>> Have you tried doing a read at CL=ALL? If it's an actual
>>>>>>> inconsistency issue (missing data), this should cause the correct
results
>>>>>>> to be returned. You'll need to run a repair to fix the inconsistencies.
>>>>>>>
>>>>>>> If all the data is actually there, you might have one or several
>>>>>>> nodes that aren't identifying the correct replicas.
>>>>>>>
>>>>>>> Arvydas
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Mar 16, 2017 at 5:31 PM, srinivasarao daruna <
>>>>>>> sree.srinu38@gmail.com> wrote:
>>>>>>>
>>>>>>> Hi Team,
>>>>>>>
>>>>>>> We are struggling with a problem related to cassandra counts,
after
>>>>>>> backup and restore of the cluster. Aaron Morton has suggested
to send this
>>>>>>> to user list, so some one of the list will be able to help me.
>>>>>>>
>>>>>>> We are have a rest api to talk to cassandra and one of our query
>>>>>>> which fetches count is creating problems for us.
>>>>>>>
>>>>>>> We have done backup and restore and copied all the data to new
>>>>>>> cluster. We have done nodetool refresh on the tables, and did
the nodetool
>>>>>>> repair as well.
>>>>>>>
>>>>>>> However, one of our key API call is returning inconsistent results.
>>>>>>> The result count is 0 in the first call and giving the actual
values for
>>>>>>> later calls. The query frequency is bit high and failure rate
has also
>>>>>>> raised considerably.
>>>>>>>
>>>>>>> 1) The count query has partition keys in it. Didnt see any read
>>>>>>> timeout or any errors from api logs.
>>>>>>>
>>>>>>> 2) This is how our code of creating session looks.
>>>>>>>
>>>>>>> val poolingOptions = new PoolingOptions
>>>>>>>     poolingOptions
>>>>>>>       .setCoreConnectionsPerHost(HostDistance.LOCAL, 4)
>>>>>>>       .setMaxConnectionsPerHost(HostDistance.LOCAL, 10)
>>>>>>>       .setCoreConnectionsPerHost(HostDistance.REMOTE, 4)
>>>>>>>       .setMaxConnectionsPerHost( HostDistance.REMOTE, 10)
>>>>>>>
>>>>>>> val builtCluster = clusterBuilder.withCredentials(username,
>>>>>>> password)
>>>>>>>       .withPoolingOptions(poolingOptions)
>>>>>>>       .build()
>>>>>>> val cassandraSession = builtCluster.get.connect()
>>>>>>>
>>>>>>> val preparedStatement = cassandraSession.prepare(state
>>>>>>> ment).setConsistencyLevel(ConsistencyLevel.QUORUM)
>>>>>>> cassandraSession.execute(preparedStatement.bind(args :_*))
>>>>>>>
>>>>>>> Query: SELECT count(*) FROM table_name WHERE parition_column=?
AND
>>>>>>> text_column_of_clustering_key=? AND date_column_of_clustering_key<=?
>>>>>>> AND date_column_of_clustering_key>=?
>>>>>>>
>>>>>>> 3) Cluster configuration:
>>>>>>>
>>>>>>> 6 Machines: 3 seeds, we are using apache cassandra 3.9 version.
Each
>>>>>>> machine is equipped with 16 Cores and 64 GB Ram.
>>>>>>>
>>>>>>>         Replication factor is 3, and write consistency is ONE
and
>>>>>>> read consistency is QUORUM.
>>>>>>>
>>>>>>> 4) cassandra is never down on any machine
>>>>>>>
>>>>>>> 5) Using cassandra-driver-core artifact with 3.1.1 version in
the
>>>>>>> api.
>>>>>>>
>>>>>>> 6) nodetool tpstats shows no read failures, and no other failures.
>>>>>>>
>>>>>>> 7) Do not see any other issues from system.log of cassandra.
We just
>>>>>>> see few warnings as below.
>>>>>>>
>>>>>>> Maximum memory usage reached (512.000MiB), cannot allocate chunk
of
>>>>>>> 1.000MiB
>>>>>>> WARN  [ScheduledTasks:1] 2017-03-14 14:58:37,141
>>>>>>> QueryProcessor.java:103 - 88 prepared statements discarded in
the last
>>>>>>> minute because cache limit reached (32 MB)
>>>>>>> The first api call returns 0 and the api calls later gives right
>>>>>>> values.
>>>>>>>
>>>>>>> Please let me know, if any other details needed.
>>>>>>> Could you please have a look at this issue once and kindly give
me
>>>>>>> your inputs? This issue literally broke the confidence on Cassandra
from
>>>>>>> our business team.
>>>>>>>
>>>>>>> Your inputs will be really helpful.
>>>>>>>
>>>>>>> Thank You,
>>>>>>> Regards,
>>>>>>> Srini
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Ryan Svihla
>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Thanks,
>>>>> Ryan Svihla
>>>>>
>>>>>
>>>>
>>>
>

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