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

Question : Batch operation is isolated if it includes changes to more than one partition.

1. True
2. False

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Explanation: Cassandra write and delete operations are performed with full row-level isolation. This means that a
write to a row within a single partition on a single node is only visible to the client performing the operation a" the
operation is restricted to this scope until it is complete. All updates in a batch operation belonging to a given partition
key have the same restriction. However, a Batch operation is not isolated if it includes changes to more than one partition.




Question : All writes to a replica node are recorded in which of the following before they are acknowledged as a success



1. In Memory

2. commit log

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4. 1,2

5. 1,2 and 3

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Explanation: Writes in Cassandra are durable. All writes to a replica node are recorded both in memory and in a
commit log on disk before they are acknowledged as a success. If a crash or server failure occurs before the memtables are
flushed to disk, the commit log is replayed on restart to recover any lost writes. In addition to the local durability (data
immediately written to disk), the replication of data on other nodes strengthens durability.




Question : In Cassandra data updates are performed as "compare (validation a condition) before setting (read before write)
" is known as


1. Consistent Transaction

2. Eventual Consistent Transaction

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4. Durable Transaction


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Explanation: The Paxos protocol is implemented in Cassandra with linearizable consistency, that is sequential
consistency with real-time constraints. Linearizable consistency ensures transaction isolation at a level similar to the
serializable level offered by RDBMSs. This type of transaction is known as compare and set (CAS); replica data is compared and
any data found to be out of date is set to the most consistent value. In Cassandra, the process combines the Paxos protocol
with normal read and write operations to accomplish the compare and set operation.

The Paxos protocol is implemented as a series of phases:
Prepare/Promise
Read/Results
Propose/Accept
Commit/Acknowledge
These phases are actions that take place between a proposer and acceptors. Any node can be a proposer, and multiple proposers
can be operating at the same time. For simplicity, this description will use only one proposer. A proposer prepares by sending
a message to a quorum of acceptors that includes a proposal number. Each acceptor promises to accept the proposal if the
proposal number is the highest they have received. Once the proposer receives a quorum of acceptors who promise, the value for
the proposal is read from each acceptor and sent back to the proposer. The proposer figures out which value to use and
proposes the value to a quorum of the acceptors along with the proposal number. Each acceptor accepts the proposal with a
certain number if and only if the acceptor is not already promised to a proposal with a high number. The value is committed
and acknowledged as a Cassandra write operation if all the conditions are met.
These four phases require four round trips between a node proposing a lightweight transaction and any cluster replicas
involved in the transaction. Performance will be affected. Consequently, reserve lightweight transactions for situations where
concurrency must be considered.

Lightweight transactions will block other lightweight transactions from occurring, but will not stop normal read and write
operations from occurring. Lightweight transactions use a timestamping mechanism different than for normal operations and
mixing LWTs and normal operations can result in errors. If lightweight transactions are used to write to a row within a
partition, only lightweight transactions for both read and write operations should be used.

Related Questions

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Question : What is true about Chebotko Diagram ?


1. These diagrams are graphical representation of Cassandra database schema design

2. They Helps, on Documenting Logical Data Model

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4. 1 and 2

5. 1,2 and 3



Question : Which is true about logical and physical data model ?

A. Logical level shows column name and its properties
B. Physical level shows column name and its properties
C. Logical level shows column name , its properties and column data type
D. Physical level shows column name , its properties and column data type


1. A,B
2. B,C
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4. A,D
5. B,D


Question : Which is true about Chebotko Diagram notation ?



1. Counter is represented as ++

2. Secondary index represented as IDX

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4. 1 and 3

5. 1 and 2


Question : Which all are true for Cassandra data modeling principal?

A. You must know your data
B. You know all your queries in advance
C. Wherever required de-normalize your data
D. You can store duplicate data


1. A,B,C
2. B,C,D
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4. A,B,D
5. A,B,C,D


Question : In Cassandra, following scenarios can be considered as an ideal.

To fetch the data, Query needs to access all the partitions in a table, to retrieve results.


1. True
2. False


Question : Cassandra prefer space compare to time , while designing data modeling?

1. True
2. False