Cassandra Components
The components of Cassandra can be divided into the following categories:
Node
A node in Apache Cassandra is the fundamental component of Cassandra’s infrastructure. It is a fully working machine that communicates with the cluster's other nodes across a fast internal network. The Gossip Protocol is the name of this network. Each node in Cassandra is issued a set of tokens. Importantly, each node in the ring is self-contained and serves the same purpose. A node in Apache Cassandra is organized into a peer-to-peer network. The node contains the actual data. A cluster node can accept read and write requests. As a result, it makes no difference where the data sits in the cluster. We'll always acquire the most recent version of the data.
Virtual Node
Virtual nodes, or vnodes for short, are used in newer Cassandra versions. A virtual node is the server’s data storage layer. By default, each server has 256 virtual nodes. As mentioned in the preceding paragraph, each node is issued a set of tokens. Every virtual node uses a subset of tokens from the node it belongs to. These virtual nodes increase the system’s versatility. As a result, Cassandra finds it easy to add more nodes to the cluster as needed. When our data has unequally distributed tokens across nodes, we can easily increase storage capacity by extending virtual nodes to the most heavily loaded node.
Server
When we say server, we mean a machine that has the Cassandra software installed. Cassandra, which is essentially a server, is installed on each node. As previously stated, each Cassandra instance now contains 256 virtual nodes. The Cassandra server is responsible for fundamental processes. For example, procedures such as replica replication or request routing.
Rack
A Cassandra rack is a logical grouping of ring nodes. A rack, in other terms, is a group of servers. The database employs racks to ensure replicas are scattered across different logical groupings. As a result, it can send operations to multiple nodes rather than just one. Multiple nodes, each in its rack, can improve fault tolerance and availability.
Data Centers
A data center is a logical configuration of racks. At least one rack should be present in the data center. The Cassandra Datacenter is a collection of nodes that are linked and configured within a cluster for replication reasons. As a result, it aids in reducing latency, preventing transactions from being impacted by other workloads and other related impacts. Furthermore, the replication factor can be configured to write to various data centers. Cassandra can thus provide more flexibility in architectural design and organization.
Cluster
A cluster is a component consisting of one or more data centers. It is the database’s most remote storage container. One or more clusters can be found in a single database. First, we have clusters made up of data centers. We have nodes inside data centers that have 256 virtual nodes by default.
Data Replication
Producing and maintaining multiple copies of data across different nodes in a cluster is called data replication in Cassandra. Some systems simply cannot tolerate data loss or interruptions in data supply. When an issue occurs, the remedy is to create a backup. It could be hardware issues, or links could go down anytime during the data process. Cassandra replicates data across numerous nodes to ensure dependability and fault tolerance. The following are the key points concerning data replication in Cassandra:
Replication Factor
The replication factor and replication technique can be used to determine the number of replicas and their placement. The replication factor is the total number of replicas in the cluster. When we set this factor to one, it signifies that each row in a cluster has just one copy, and so on. This factor can be configured at the data center and rack levels.
Replication Strategy
The replication strategy governs how replicas are selected. The value of replicas is the same. Cassandra employs two methods to determine which nodes contain replicated data. The SimpleStrategy is the first, and it is uninformed of the logical segmentation of nodes for data centers and racks. The second one, NetworkTopologyStrategy, is more sophisticated and considers racks and data centers. Using The NetworkTopologyStrategy, we may specify how many copies should be put in different data centers. Furthermore, it avoids scenarios where two clones are placed on the same rack.
Node in Apache Cassandra
Each node in Apache Cassandra stores the actual Data and Information such as its location, data center details, etc. Keyspaces, tables, and the data schema are also included. A node can conduct operations like reading, writing, and deleting data. Cassandra clusters are made up of nodes. Each node in the cluster is connected peer-to-peer and is equivalent to every other node, forming a ring-like topology.
Types of Nodes
Apache Cassandra has three sorts of nodes: seed, regular, and client nodes.
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The cluster's bootstrapping is the responsibility of the seed nodes. It searches for other nodes in the cluster.
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Nodes that store data and participate in read-and-write activities are known as regular nodes.
- Client nodes are used to access the cluster's data. However, they do not save any data.
Nodetool
Nodetool is a node management utility tool that gives information about node health, nodes, and clusters. You may retrieve all relevant node information by using nodetool commands. Commands like “help,” “info,” and “status” provide general information about the node. By default, Nodetool is located in the bin/ subdirectory, where Cassandra is installed.
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help: It displays a list of all possible node tool commands.
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status: It displays the node's status and provides basic health information.
- info: It offers information on the node's current configuration and statistics.
Node Operations
Apache Cassandra nodes carry out a variety of operations to ensure data consistency and fault tolerance:
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Nodes carry out read-and-write operations to save and retrieve data.
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Nodes connect with one another and share details about the cluster via the gossip protocol.
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Nodes carry out anti-entropy procedures to find and fix data discrepancies.
- Nodes carry out repair operations to make up for discrepancies among other nodes in the cluster.
Adding and Removing Nodes in Apache Cassandra
The following are the general steps for adding or removing a node in Cassandra:
Adding Nodes
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Ensure that the new node is running the same Cassandra version and configuration as the current nodes.
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On the new node, update the Cassandra configuration file. Set the name of the cluster, the first token, the listen address, and the seed nodes.
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Cassandra should be started on the new node. It will connect to the cluster and start streaming data from existing nodes.
- To ensure that the new node enters the cluster and completes the streaming process correctly, use tools such as nodetool, Cassandra logs, etc.
Removing Nodes
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Check that the replication factor is appropriate for the desired level of fault tolerance.
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Execute the nodetool decommission command on the node that you want to remove.
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Monitor the node's state to ensure that it is successfully deactivated. To validate the node's removal, use tools such as nodetool or a monitoring system.
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After deleting the node, update the Cassandra configuration files (cassandra.yaml) on the remaining nodes by removing the IP address of the decommissioned node from the seed nodes list and any other necessary parameters.
Also see, Checkpoint in DBMS and Recursive Relationship in DBMS
Frequently Asked Questions
What is the concept of tunable consistency in Cassandra?
Cassandra’s tunable consistency is a fantastic feature that makes it a popular database choice among developers, analysts, and big data architects. Cassandra’s adjustable consistency allows users to choose the consistency level most suited to their use cases.
How does Cassandra write?
Cassandra writes using two commits: first, it writes to a disc commit log, and then it commits to an in-memory structure known as memtable. The write is complete after the two commits are successful. Writes are stored as SS Tables in the table structure. Cassandra provides better writing performance.
What is CQL?
CQL is a Cassandra Query Language used to access and query an Apache-distributed database, and it includes a CQL parser that sends all implementation information to the server. CQL syntax is comparable to SQL; however, it has no effect on the Cassandra data model.
What is Super Column in Cassandra?
Cassandra Super Column is a one-of-a-kind element made up of related data collections. They are key-value pairs with values as columns. Super column data elements have no independent values and are only used to collect data from other columns.
Conclusion
This article explains the concepts of Cassandra components, Data Replication, and Node in Apache Cassandra, along with some frequently asked questions related to the topic. I hope this article node in Apache Cassandra was beneficial and you learned something new. To better understand the topic, you can refer to amazon keyspaces for apache cassandra, database integration in Express, and types of NoSQL databases.
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