Question:- Explain the concept of tunable consistency in Cassandra.
Answer:- Tunable consistency is a phenomenal character that makes Cassandra a favored database choice of Developers, Analysts, and Big data Architects. Consistency refers to the up-to-date and synchronized data rows on all their replicas. Cassandra’s tunable consistency allows users to select the consistency level best suited for their use cases. It supports two consistencies: eventual consistency and strong consistency. The former guarantees consistency when no new updates are made on a given data item, i.e., all accesses return the last updated value eventually. Systems with eventual consistency are known to have achieved replica convergence. For strong consistency, Cassandra supports the following condition: R + W > N where, N – Number of replicas W – Number of nodes that need to agree for a successful write R – Number of nodes that need to agree for a successful read
Question:- How does Cassandra write?
Answer:- Cassandra performs the write function by applying two commits: first, it writes to a commit log on the disk, and then it commits to an in-memory structure known as memtable. Once the two commits are successful, the write is achieved. Writes are written in the table structure as SSTables (sorted string tables). Cassandra offers faster write performance.
Question:- Define the management tools in Cassandra.
Answer:- DataStax OpsCenter: It is the Internet-based management and monitoring solution for Cassandra cluster and DataStax. It is free to download and includes an additional edition of OpsCenter. SPM primarily administers Cassandra metrics and various OS and JVM metrics. Besides Cassandra, SPM also monitors Hadoop, Spark, Solr, Storm, ZooKeeper, and other Big Data platforms. The main features of SPM include correlation of events and metrics, distributed transaction tracing, creating real-time graphs with zooming, anomaly detection, and heartbeat alerting.
Question:- Define memtable.
Answer:- Similar to a table, a memtable is the in-memory/write-back cache space consisting of the content in a key and column format. The data in a memtable is sorted by key, and each column family consists of a distinct memtable that retrieves column data via the key. It stores the writes until it is full, and then flushes them out.
Question:- What is SSTable? How is it different from other relational tables?
Answer:- SSTable expands to ‘Sorted String Table,’ which refers to an important data file in Cassandra and accepts regular written memtables. They are stored on disk and exist for each Cassandra table. Exhibiting immutability, SSTables do not allow any further addition and removal of data items once written. For each SSTable, Cassandra creates three separate files like partition index, partition summary, and a bloom filter.
Question:- Explain the concept of Bloom Filter.
Answer:- Associated with SSTable, Bloom filter is an off-heap (off the Java heap to native memory) data structure to check whether there is any data available in the SSTable before performing any I/O disk operation.
Question:- Explain CAP Theorem.
Answer:- With a strong requirement to scale systems when additional resources are needed, CAP Theorem plays a major role in maintaining the scaling strategy. It is an efficient way to handle scaling in distributed systems. Consistency, availability, and partition tolerance (CAP) theorem states that in distributed systems like Cassandra, users can enjoy only two out of these three characteristics. One of them needs to be sacrificed. Consistency guarantees the return of most recent write for the client; availability returns a rational response within minimum time; and in partition tolerance, the system will continue its operations when network partitions occur. The two options available are AP and CP.
Question:- State the differences between a node, a cluster, and a data center in Cassandra.
Answer:- There are various components of Cassandra. While a node is a single machine running Cassandra, cluster is a collection of nodes that have similar types of data grouped together. Data centers are useful components when serving customers in different geographical areas. You can group different nodes of a cluster into different data centers.
Question:- How to write a query in Cassandra?
Answer:- Using CQL (Cassandra Query Language) we can write queries in Cassandra. Cqlsh is used for interacting with the database.
Question:- What OS does Cassandra support?
Answer:- Cassandra supports both Windows and Linux.
Question:- What is Cassandra Data Model?
Answer:- Cassandra data model consists of four main components: Cluster: Made up of multiple nodes and keyspaces Keyspace: A namespace to group multiple column families, especially one per partition Column: Consisting of a column name, value, and timestamp Column Family: Multiple columns with the row key reference
Question:- What is CQL?
Answer:- CQL is Cassandra query language to access and query Apache distributed database. It consists of a CQL parser that incites all the implementation details to the server. The syntax of CQL is similar to SQL, but it does not alter the Cassandra data model.
Question:- Explain the concept of compaction in Cassandra.
Answer:- Compaction refers to a maintenance process in Cassandra, in which the SSTables are reorganized for data optimization of data structures on the disk. The compaction process is useful during interacting with memtables. There are two types of compaction in Cassandra. • Minor compaction: It gets started automatically when a new SSTable is created. Here, Cassandra condenses all the equally sized SSTables into one. • Major compaction: It is triggered manually using the nodetool. It compacts all SSTables of a column family into one.
Question:- Does Cassandra support ACID transactions?
Answer:- Unlike relational databases, Cassandra does not support ACID transactions.