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From Shrikar archak <shrika...@gmail.com>
Subject Re: Read performance in map data type
Date Thu, 03 Apr 2014 07:15:45 GMT
Hi Apoorva,
As per the cfhistogram there are some rows which have more than 75k columns
and around 150k reads hit 2 SStables.

Are you sure that you are seeing more than 500ms latency?  The cfhistogram
should the worst read performance was around 51ms
which looks reasonable with many reads hitting 2 sstables.

Thanks,
Shrikar


On Wed, Apr 2, 2014 at 11:30 PM, Apoorva Gaurav
<apoorva.gaurav@myntra.com>wrote:

> Hello Shrikar,
>
> We are still facing read latency issue, here is the histogram
> http://pastebin.com/yEvMuHYh
>
>
> On Sat, Mar 29, 2014 at 8:11 AM, Apoorva Gaurav <apoorva.gaurav@myntra.com
> > wrote:
>
>> Hello Shrikar,
>>
>> Yes primary key is (studentID, subjectID). I had dropped the test table,
>> recreating and populating it post which will share the cfhistogram. In such
>> case is there any practical limit on the rows I should fetch, for e.g.
>> should I do
>>        select * form marks_table where studentID = ? limit 500;
>> instead of doing
>>        select * form marks_table where studentID = ?;
>>
>>
>> On Sat, Mar 29, 2014 at 5:20 AM, Shrikar archak <shrikar84@gmail.com>wrote:
>>
>>> Hi Apoorva,
>>>
>>> I assume this is the table with studentId and subjectId  as primary keys
>>> and not other like like marks in that.
>>>
>>> create table marks_table(studentId int, subjectId int, marks int,
>>> PRIMARY KEY(studentId,subjectId));
>>>
>>> Also could you give the cfhistogram stats?
>>>
>>> nodetool cfhistograms <your keyspace> marks_table;
>>>
>>>
>>>
>>> Thanks,
>>> Shrikar
>>>
>>>
>>> On Fri, Mar 28, 2014 at 3:53 PM, Apoorva Gaurav <
>>> apoorva.gaurav@myntra.com> wrote:
>>>
>>>> Hello All,
>>>>
>>>> We've a schema which can be modeled as (studentID, subjectID, marks)
>>>> where combination of studentID and subjectID is unique. Number of studentID
>>>> can go up to 100 million and for each studentID we can have up to  10k
>>>> subjectIDs.
>>>>
>>>> We are using apahce cassandra 2.0.4 and datastax java driver 1.0.4. We
>>>> are using a four node cluster, each having 24 cores and 32GB memory. I'm
>>>> sure that the machines are not underperformant as on same test bed we've
>>>> consistently received <5ms response times for ~1b documents when queried
>>>> via primary key.
>>>>
>>>> I've tried three approaches, all of which result in significant
>>>> deterioration (>500 ms response time) in read query performance once number
>>>> of subjectIDs goes past ~100 for a studentID. Approaches are :-
>>>>
>>>> 1. model as (studentID int PRIMARY KEY, subjectID_marks_map map<int,
>>>> int>) and query by subjectID
>>>>
>>>> 2. model as (studentID int, subjectID int, marks int, PRIMARY
>>>> KEY(studentID, subjectID) and query as select * from marks_table where
>>>> studentID = ?
>>>>
>>>> 3. model as (studentID int, subjectID int, marks int, PRIMARY
>>>> KEY(studentID, subjectID) and query as select * from marks_table where
>>>> studentID = ? and subjectID in (?, ?, ?....?)  number of subjectIDs in
>>>> query being ~1K.
>>>>
>>>> What can be the bottlenecks. Is it better if we model as (studentID
>>>> int, subjct_marks_json text) and query by studentID.
>>>>
>>>> --
>>>> Thanks & Regards,
>>>> Apoorva
>>>>
>>>
>>>
>>
>>
>> --
>> Thanks & Regards,
>> Apoorva
>>
>
>
>
> --
> Thanks & Regards,
> Apoorva
>

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