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Arpit Bhayani Blogs
001 Ai Topological Sort

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TLDR: How Writes Work in Apache Cassandra

Date: 2025-10-20 Source: https://arpitbhayani.me/blogs/cassandra-writes

Overview

Apache Cassandra is a distributed database designed for high availability and horizontal scalability. This write-up explores the complete write path in Cassandra, from the moment a client sends a write request to how data gets replicated across nodes in the cluster.

Key Points

  • Apache Cassandra is a distributed database designed for high availability and horizontal scalability.
  • Client Connection and Coordinator Selection: Every write request in Cassandra starts with a client connecting to any node in the cluster.
  • Determining Replica Nodes: Before the coordinator can forward writes, it needs to determine which nodes should store the data.
  • The Write Path Within a Node: Once the coordinator determines which nodes should receive the write, it forwards the mutation to those nodes.
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003 Rag Production
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004 Structure Of Llm Chat
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113 Replication Formats
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115 Master Replica Replication
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116 Durability
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117 Isolation
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  • Consistency Levels: The consistency level determines how many replica nodes must acknowledge a write before the coordinator responds to the client.
  • Here’s an Example: Consider a cluster with a replication factor of 3, and you issue a write with consistency level QUORUM: Timeline: The entire operation typically completes in 2-5ms, depending on network latency and load.

    • Takeaway

    Cassandra uses a Log-Structured Merge (LSM) tree to hold the data, where writes are first persisted to an append-only CommitLog before being written to an in-memory MemTable.