Apache Cassandra is an open-source distributed database that can handle "big data" workloads by distributing data and reads across multiple nodes without a single point of failure. It uses a Log Structured Merge (LSM) storage engine, which includes a commit log, memtable, SSTables, and compaction processes to ensure data integrity and performance. Cassandra is written in Java and has limitations due to its garbage collection issues, which can lead to performance problems. In contrast, YugabyteDB is implemented in C++ with no need for garbage collection, offering better throughput and predictable response times. Cassandra prioritizes availability and partition tolerance over consistency, while YugabyteDB ensures stronger consistency and ACID transactions. Lightweight Transactions (LWT) are used in Cassandra to provide conditional inserts/updates, but require four round trips, whereas YugabyteDB supports them with just one round-trip. Cassandra's secondary indexes can be beneficial for query performance, but have limitations due to their distributed nature. YugabyteDB provides consistent and ACID-compliant secondary indexes built on its distributed transactions. For multi-region deployments, Cassandra uses LOCAL_QUORUM consistency, while YugabyteDB offers global or regional consistency with continuous availability under region failures or zone/rack failures, respectively.