If going by Month as partition key then you need to duplicate the data. I dont
think going with name as partition key is good datamodel practice as it will
create a hotspot. Also I believe your queries will be mostly by employee not by
month.
You can create employee id as partition key and month as clustering and keep
employee details as static columns so they wont be repeated Naidu Saladi
From: Srinivasa T N <seen...@gmail.com>
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Sent: Tuesday, July 7, 2015 3:07 AM
Subject: Re: Example Data Modelling
Thanks for the inputs.
Now my question is how should the app populate the duplicate data, i.e., if I
have an employee record (along with his FN, LN,..) for the month of Apr and
later I am populating the same record for the month of may (with salary
changed), should my application first read/fetch the corresponding data for apr
and re-insert with modification for month of may?
Regards,
Seenu.
On Tue, Jul 7, 2015 at 11:32 AM, Peer, Oded <oded.p...@rsa.com> wrote:
The data model suggested isn’t optimal for the “end of month” query you want to
run since you are not querying by partition key.The query would look like
“select EmpID, FN, LN, basic from salaries where month = 1” which requires
filtering and has unpredictable performance. For this type of query to be fast
you can use the “month” column as the partition key and the “EmpID” and the
clustering column.This approach also has drawbacks:1. This data model creates a
wide row. Depending on the number of employees this partition might be very
large. You should limit partition sizes to 25MB2. Distributing data according
to month means that only a small number of nodes will hold all of the salary
data for a specific month which might cause hotspots on those nodes. Choose the
approach that works best for you. From: Carlos Alonso
[mailto:i...@mrcalonso.com]
Sent: Monday, July 06, 2015 7:04 PM
To: user@cassandra.apache.org
Subject: Re: Example Data Modelling Hi Srinivasa, I think you're right, In
Cassandra you should favor denormalisation when in RDBMS you find a
relationship like this. I'd suggest a cf like thisCREATE TABLE salaries (
EmpID varchar, FN varchar, LN varchar, Phone varchar, Address varchar,
month integer, basic integer, flexible_allowance float, PRIMARY KEY(EmpID,
month)) That way the salaries will be partitioned by EmpID and clustered by
month, which I guess is the natural sorting you want. Hope it helps,Cheers!
Carlos Alonso | Software Engineer | @calonso On 6 July 2015 at 13:01, Srinivasa
T N <seen...@gmail.com> wrote:Hi, I have basic doubt: I have an RDBMS with
the following two tables:
Emp - EmpID, FN, LN, Phone, Address
Sal - Month, Empid, Basic, Flexible Allowance
My use case is to print the Salary slip at the end of each month and the
slip contains emp name and his other details.
Now, if I want to have the same in cassandra, I will have a single cf with
emp personal details and his salary details. Is this the right approach?
Should we have the employee personal details duplicated each month?
Regards,
Seenu.
