Apache Cassandra is a free and open-source, distributed, wide column store, NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure.Cassandra offers robust support for clusters spanning multiple datacenters, with asynchronous masterless replication allowing low latency … This means each node stores records that hash to any of the vnode ranges it is responsible for. In this table column 1 having the primary key. When the in-memory data structure crosses a predefined threshold, it is dumped to the disk along with an index file for fast lookups. There can also be multiple column families that relate to the concept of relational table. Virtual tables are local only and non distributed; Virtual tables have no associated SSTables ; Consistency level of the queries sent virtual tables are ignored; Virtual tables are managed by Cassandra and a user cannot run DDL to create new virtual tables or DML to modify existing virtual tables; Virtual tables are created in special keyspaces and not just any keyspace; All existing virtual tables use LocalPartitioner. Now, let’s take an example of how user data distributes over cluster. Cassandra solves these issues by periodically analyzing the load information in the ring and repositioning the lightly loaded nodes on the ring to alleviate high load nodes. The idea is to represent $\phi$ on a dynamically adjustable scale, which reflects network and load conditions at the monitored nodes. With consistent hash sharding, data is evenly and randomly distributed across shards using a partitioning algorithm. A distributed SQL database needs to automatically partition the data in a table and distribute it across nodes. As with Riak, which I wrote about in 2013, Cassandra remains one of the core active distributed database projects alive today that provides an effective and reliable consistent hash ring for the clustered distributed database system. Index Terms— cassandra, database, distributed hash table, distributed systems 1.Introduction assandra[1] is a distributed data storage system developed initially by Facebook engineers to facilitate large scale distributed search in a rapidly resource-fluctuating network. Apache Cassandra was originally developed at Facebook after that it was open sourced in 2008 and after that it become one of a top level Apache project in 2010. 1. In Cassandra nodes are placed in a virtual ring and the mapping of both keys and nodes position is done using a hash function. The distribution and replication depending on the partition key, key value and Token range. Cassandra is a O(1)-hop routing Distributed Hash table which is eventually consistent and tunable trade-offs between consistency and latency. The consistent hash function is used to hash the data key to generate identifiers. Cassandra is a Distributed NoSQL database means all the data is distributed across the Cluster. Section 3 discusses distributed hash table (DHT) the-ory with section 3.1 going into more detail on how Cassandra’s implementation of a DHT enables fault tolerance and load balancing within the cluster. Section 4 builds on previous sections with a deeper discussion of Cassandra’s architecture. Cassandra can provide a highly available service without a single point of failure. Cassandra partitions data over the storage nodes using a variant of consistent hashing for data distribution. 2nd row contains two columns (column 1 and column 3) and its values. 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