Cassandra Interview Questions
We will mention Cassandra Interview Questions in 2021 for you in this article.
- Define Cassandra. What is the significance of Cassandra and why should you utilize it?
Cassandra is a massively efficient, high-performance data warehouse that could also manage vast amounts of data over a large number of commodity systems while ensuring full availability and minimizing data loss. It’s a NoSQL database type. The database was created to enable Facebook’s inbox search functionality, allowing users to discover conversations and other items they’re concerned about rapidly.
Cassandra’s use is influenced by a number of elements like:
- Scalabilities ranging from gigabytes to petabytes
- It’s a database that’s based on columns.
- There is no weak point or failure.
- There is no necessity for a separate cached layer.
- Designing a flexible schema It offers versatile data storage, simple data transmission, and quick writing speeds.
- It implements the properties like Atomicity, Consistency, Isolation, and Durability, shortly known as ACID.
- Cloud and multi-datacenter capabilities compaction of data.
- Define NOSQL. NoSQL database types are classified into how many categories?
Relational tables store and manage data uniquely than noon – tabular NoSQL ( known as not only SQL”) databases. The data model of NoSQL databases is used to classify them. The most similar types of documents are doc, key-value, wide-column, and graphs. They feature customizable schemas and can easily manage large quantities of data and high user demands.
NoSQL databases are classified into four categories:
- Key-Value Store
- Document Store
- Column Store
- Graph Databases
- What specifically do you mean by Cassandra logging. Describe the various Cassandra logging levels.
The system keeps track of logs. In the Cassandra logging directory, there are two files: log and debug.log.Logging may be set up either programmatically or directly. Increase the logging level, which is set to INFO by default, to make the results more verbose, and you’ll have a better idea of what’s going on in your database.
- ALL: This refers to all levels, particularly custom levels.
- DEBUG: Designates coarser-grained instructional events.
- TRACE: Designates finer-grained informative events.
- INFO: This is for instructive notifications that emphasize performance at a coarse level.
- WARN: Indicates a situation that might be dangerous.
- ERROR: Defines error occurrences that may or may not prevent the program from continuing to operate.
- OFF: This is the maximum available level and is used to disable/put out of the action of logging.
- Define Cassandra – CQLsh and What is Cassandra- CQL collections.
Cassandra-CQlsh is a language of query for communicating with Cassandra’s database. You can accomplish a few things like Creating a schema, inserting information, and running a query with Cassandra cqlsh. CQL collections in Cassandra allow us to store more values in a variable. CQL collections may be used in Cassandra in the following ways.
- LIST: When the order of the data must be retained, and a value must be recorded several times, this type of data is utilized.
- SET: It is used to store and retrieve a set of compounds in proper order
- How is the data written and stored in Cassandra?
Cassandra guarantees that the bytes are encoded correctly when you specify the validator as the data is stored in bytes. The column is then ordered using a comparator depending on the encoding’s particular ordering. Cassandra publishes data to a commit log first, then to the memtable in-memory table structure, and finally to SStable.
- Data is logged in the commit log.
- Data is written to the memtable.
- Data from the memtable is being flushed.
- SSTables are used to store data on a disc.
- Cassandra supports how many different forms of configurable consistency?
It generally supports two types of consistency: Eventual and strong consistency. When no new changes are made to a data item, eventual consistency is utilized, and all accesses finally return the last modified value. Replica convergence is a term used to describe systems that attain eventual consistency. Cassandra maintains the strong consistency requires the following conditions:
N = R + W
N is the number of clones in this case.
W is the number of nodes that must concur in order for a writer to succeed.
R is the number of nodes that must agree in order for a read to be effective.
- Tell us about the query language that Cassandra Database uses.
Cassandra Database makes use of the Cassandra query language. It is a user interface via which a user may access a database. It is fundamentally a medium of communication. This panel is where all of the operations are executed.
- Who created Cassandra and on which platforms is it available?
Cassandra was created at Facebook by Avinash Lakshman, one of the inventors of Amazon’s Dynamo, and Prashant Malik to enable the Facebook inbox search functionality. Cassandra was launched as an open-source project on Google code by Facebook in July 2008. Cassandra is a Java application that may operate on any Java-based platform, including the Java Runtime Environment aka (JRE) and the Java Virtual Machine aka (JVM). Cassandra is also available for Red Hat, CentOS, Debian, and Ubuntu Linux.
- How does Cassandra get rid of data?
SSTables are permanent. Therefore you can’t delete a row from them. Cassandra replaces the column value with a high value called Tombstone when a row has to be destroyed. The Tombstone value is deemed erased when the data is recorded.
- What is the variation between a direct request, a digest request, and a read repair request?
- DIRECT REQUEST: The read operation in Cassandra includes a direct request. The coordinator node communicates with the replica node in this manner.
- DIGEST REQUEST: When the coordinator node makes contact with replicas, it always asks for the nodes that respond the quickest. The contacted nodes then respond with a digest of the needed data.
- READ REPAIR REQUEST: When the coordinator node makes requests, it checks in with the nodes to see if they have any outdated information. This data is transmitted to be read and repaired in the background before being replaced with the new data. Read and repair requests are a way to maintain the data current while also ensuring that the requested row is consistent across all replicates.
- What do you mean by Data replication?
Data replication is the process of transmitting data from one node to other nodes in the cluster. This process enables database replication and fault-tolerant. The replication factor determines the level of copies, whereas the replication method determines which nodes are used to copy the data. A replication factor of two indicates that each row is duplicated twice, each on a distinct node. There is no primary or master replica; all replicas are equally significant. A replication factor of one indicates that each row in the Cassandra cluster has only one copy.
- Define MemTable and SST Table and what is the difference between them?
In a MemTable, data is recorded and stored temporarily. After the data in the commit, the log has been completed, it is written to memtable. In Cassandra, Memtable is a ramge. Because each column category has its own MemTable, data in MemTable is categorized into a key, and data is retrieved using the key. When the write memory is filled, the messages are automatically deleted. Sorted String Table’ is another acronym for SSTable. SSTable is a Cassandra data file whose primary purpose is to store data flushed from memtable. SSTbale, unlike MemTable, does not destroy data or allow future additions after it has been created. In MemTable, it doesn’t store the data. It cannot store into a disk, but it temporarily build-up to ‘write data’. Whereas in SStable, it is used to store the data from Memtable into the Cassandra database. The data stored in SSTable is permanent and cannot be changed.
- Explain column family and what are the characteristics of the column family in Cassandra?
In Cassandra, a column family is a set of data that are organized and methodical. It’s utilized to portray the stored data logically. At least one column family in a keyspace has these. The Cassandra column family has no schema and is very scalable. It is divided into several categories, including Static Column Family – This is where the names and data types are specified. As a result, when the column family is established, you choose to name the column name and data types. Because the columns stay static and the amount of columns accessible is known, it’s called static.
Dynamic Column Family — A dynamic column family does not define column names in advance, allowing Cassandra to store data using any application and column names. So dynamic helps in a manner because, with unstructured data, dynamic column families often assist in handling additional fields that may have been introduced later.
A column family has various qualities, and a few of them are as follows:
- The Cache of the Key
- Cache of Rows: There can be wide rows and several rows.
- Row Cache Preload
- Composite Key: It consists of one or more primary key fields
Also read My journey to VIZIT Labs as a Senior Data Engineer