DataStax Cassandra Developer Certification Certification Questions and Answer (Dumps and Practice Questions)

Question : Suppose you have following table definition

CREATE TABLE HADOOPEXAM (

id uuid,
t_id timeuuid,
name text,
description text,
price int
primary key (id, t_id);

What is the Cluster key over here?

1. id

2. t_id

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4. None of this


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Explanation: : Here (id,t_id) is a composite key and id is a primary key and t_id is a cluster key




Question : Suppose you have following table definition

CREATE TABLE HADOOPEXAM (

id uuid,
t_id timeuuid,
cours_id uuid,
name text,
description text,
price int
primary key ((id,cours_id), t_id));

What is the Cluster key overhere

1. id

2. t_id

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4. (id,cours_id)


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Explanation: Following are different variations of primary keys. Please note that COL1, COL2, COL3,a¦ and so on
represent columns in the table.

COL1: primary key has only one partition key and no cluster key.
(COL1, COL2): column COL1 is a partition key and column COL2 is a cluster key.
(COL1,COL2,COL3,): column COL1 is a partition key and columns COL2, COL3 and so on make cluster key.
(COL1, (COL2, COL3,)): It is same as 3 i.e column COL1 is a partition key and columns COL2,COL3,a¦ make cluster key.
((COL1, COL2,a¦), (COL3,COL4,a¦)): columns COL1, COL2 make partition key and columns COL3,COL4,a¦ make cluster key.

It is important to note that when compound key is COL1,COL2,COL3 then the first key COL1 becomes partition key and rest of the
keys become part of the cluster key. In order to make composite partition keys we have to specify keys in parenthesis such as:
( ( COL1,COL2) , COL3, COL4). In this case COL1 and COL2 are part of partition keys and COL3, COL4 are part of cluster key.





Question : The purpose of partition key is to identify the partition or node in the cluster which stores that row.

1. True
2. False

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Explanation: The purpose of partition key is to identify the partition or node in the cluster which stores that
row. When data is read or write from the cluster a function called Partitioner is used to compute the hash value of the
partition key. This hash value is used to determine the node/partition which contains that row. For example rows whose
partition key values range from 11000 to 11234 may reside in node A and rows with partition key values range from 11235 to
12000 may reside in node B . If a row contains partition key whose hash value is 11233 then it will be stored in node A.

Related Questions

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Question : All the statements, you write in batch will be executed in order of defined

1. True
2. False


Question : You should use Cassandra client side join, if resources don't support the necessary data duplication

1. True
2. False


Question : Which is true for Cassandra?

1. Cassandra supports join, but it needs to be avoided.

2. Cassandra does not support join at all

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4. If you have data in 3rd normal form then only you can apply joins in Cassandra



Question : . Ongoing repair operations in Cassandra ensure that all replicas of a row will eventually be _________



1. Durable

2. Active

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4. isolated



Question : As per the CAP theorem, Cassandra is a ________ database

1. CA

2. AP

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4. CAP



Question : You can tune Cassandra's consistency level ____________

1. per-operation

2. set it globally for a cluster

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4. 1 and 2

5. 1,2 and 3