What is Cassandra?
Answers:
- The Cassandra
is a free open source data storage system. It is developed by “Facebook”. It is used for “inbox search” and designed for storing and managing huge amounts of data.
The Cassandra
is a NOSQL database which has high scalability and availability.
It is highly scalable, high-performance
distributed database system and used for “Real
Time” data store system for online and it is no single point of failure.
The Cassandra
is a right choice when we need scalability and high availability without
compromising performance.
Cassandra is written in which language?
Answers:
-The Cassandra had written using “Java” language.
JMX stands for?
Answers:
- The “JMX”
stands for “Java Management Extension”.
“What is” Cassandra vs. Mongodb?
What is the advantage of Cassandra?
Answers:
- The main advantage as following as,
1. It’s is a
free Open Source.
2. It’s
supported User Defined types.
3. The idea
is based on wide column store of BigTable
and DynamoDB.
4. Its extensible
record stores and also store data in records with an ability to hold very large
numbers of dynamic columns.
5. It’s Implementation
using Java language.
6. It’s
using Server operating systems like BSD, Linux, OS X, and Windows.
7. Its schema free and secondary indexes restricted.
8. The APIs and other methods access by proprietary protocols.
9. It’s
used sharding methods for partitioning.
When should you use Cassandra?
Answers:
- The Cassandra
is a NoSQL database and does not provide ACID and relational data property and
its high scalability and availability and also no single point of failure.
How many types of NoSQL databases?
Answers:
- Right now,
4 Types of NoSQL databases as,
1. Document
Stores (MongoDB, Couchbase)
2. Column
Stores (Cassandra)
3. Key
Value Stores (Redis, Volgemort)
4. Graph
Stores (Neo4j, Giraph)
What do you understand by Commit log in Cassandra?
Answers:
- In Cassandra,
commit log is a crash recovery mechanism. Each and every write operations are
written to the commit log.
Define composite type in Cassandra?
Answers:
- Composite type allows us to defining a key or a column name with a concatenation of data of different type in Cassandra.
Here are 2 types of Composite Types as,
1. Row Key
2. Column
Name
How Cassandra stores data?
Answers:
- In Cassandra,
all the data stored as bytes. When
you specify validators, Cassandra
ensures those bytes are encoded or not as per your requirement.
This comparator
orders the column based on the ordering specific to the encoding, while
composite are just byte arrays with a specific encoding and for each components
it stores a two byte length followed by the byte encoded components
followed by a termination bit.
What is SSTable?
Answers:
- The SStable consist two files that are,
1. Index
file.
2. Data
file.
What do you understand by Node in Cassandra?
Answers:
- In Cassandra, the “Node” is the place where data is stored.
What is bloom filter?
Answers:
- The Bloom
filter is an off heap data structure and is used to
check to data availability in the SSTable
before performing any “I/O disk”
operations.
What is Thrift?
Answers:
- The Thrift
is the name of the Remote Procedure Call (RPC)
client and it used to communicate
with the Cassandra server.
What are the main components of Cassandra Data Model?
Answers:
- The Cassandra
Data Model consists of 4 major components as following as,
1. Cluster: - These
are made-up of multiple nodes and keyspaces.
2. Keyspace: - It’s a
namespace and used to group multiple column families, especially one per
partition.
3. Column: - It’s
consists of a column name, value and timestamp also.
4. Column family: - It’s
is used to refer to multiple columns with row key reference.
What is a column family in Cassandra?
Answers:
- The Column
family in Cassandra is referred for a collection of rows.
What is a cluster in Cassandra?
Answers: - “A Cluster is a container that contains
one or more data centres.”
A “Cluster”
is a container for the key-spaces and the “Cassandra”
database is segmented over multiple machines that are work together.
It is also “Outermost container” which arranges the nodes in a ring format and
assigns data to them and these nodes have a replica which used to handling the data
in case of failure.
List out the other components of Cassandra?
Answers:
- The COLLECTIONS list of the other components is,
1. Cluster
2. Node
3. SSTable
4. Mem-table
5. Data Centre
6. Commit
log
7. Bloom
Filter
8. And so
on..
What do you understand by Cluster in Cassandra?
Answers:
- “A Cluster
is a container that contains one or more data centres.”
A “Cluster”
is a container for the key-spaces and the “Cassandra”
database is segmented over multiple machines that are work together.
What do you mean by “Data Centre” in Cassandra?
Answers:
- The Cassandra “Data centre” is a collection of nodes and these nodes have a
replica which used to handling the data in case of failure.
What is a keyspace in Cassandra?
Answers:
- A Cassandra keyspace is a namespace which used
to determine the data replication on nodes and the “cluster” lies of one
keyspace per node.
What is the syntax to create keyspace in Cassandra?
Answers:
- The keyspace
is a namespace which used to determine the data replication on nodes.
Syntax: - CREATE
KEYSPACE <identifier> WITH <properties>
What are the values stored in the Cassandra Column?
Answers:
- In Cassandra, basically used 3(three) values that
is
1. Column
Name
2. Value
3. Time
Stamp
When you can use Alter keyspace?
Answers:
- The “ALTER
KEYSPACE” is used to change the properties like “number of replicas” and “durable
write” of a keyspace.
What is Cassandra Cqlsh?
Answers:
- The “Cassandra Cqlsh” is a query language which
used to enables the users to communicate with database.
For this, we can do following things that is
1. Define a
Schema
2. Insert a
Data and
3. Execute
a Query
What is mandatory while creating a table in Cassandra?
Answers:
- In the Cassandra
database, the “primary key” is mandatory key while we creating a table and we
can create one or more columns of a table.
What we need to be taken care while adding a Column?
Answers:
- In the Cassandra
database, while adding a new column you must need and follow the below points,
1. The “Column
name” is not conflicting with an “existing column” names and
2. The “Table”
is not defined with compact storage option.
Elaborate on Cassandra - CQL?
Answers:
- In Cassandra
database, the “CQL” collections are helping us to store multiple values in a
single variable.
The CQL collections are
1) List: - It’s
used for maintained the data order and stored values multiple times.
2) SET: - It’s
used for store and returned to sorted orders.
3) MAP: - It’s
a data type and used to store a key value pair of elements.
How Cassandra writes data?
Answers:
- The Cassandra writes the data in 3 components
that is,
1. Commit-log
Write
2. Memtable
Write
3. SStable
Write
What is Memtable in Cassandra?
Answers:
- The “Cassandra” writes the data to in-memory
structure that is known as Memtable.
1. It is an
in-memory cache with the content stored as the key column.
2. By the “key”,
Memtable data are sorted.
3. Each and
every column contains a separates Memtable and also is used to retrieves column
data from the key.
How Cassandra writes changed data into Commit-log?
Answers:
- The following ways as,
1. The Cassandra
concatenates (write operations) changed data to commit-log.
2. The commit-log
acts as a “crash recovery log” for the data.
3. The “commit-log”
writes operation will be never considered successful.
What is the use of “void close ()” method?
Answers:
- This “void close()” method is used to close the
current instance of the session.
What is the Replication Factor?
Answers:
- The “Replication
Factor” is a unit of the “number of existing data copies”. It’s an essential to
increase the replication factor to log into cluster.
What is the use of “ResultSet execute” method?
Answers:
- This “ResultSet execute()”method is used to
execute a query and It requires a statement object also.
How Cassandra delete Data?
Answers:
- The “SSTables” are immutable. So we can’t
remove a row from SSTables.
When a row needs to be deleted, the “Cassandra”
assigns the column value with a special value called “Tombstone” and when the
data is read, “Tombstone” value is considered as “deleted”.
So we can say that cannot delete data from the Cassandra
database.
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