Consensus is what prevents distributed systems from fracturing into multiple, conflicting realities. It ensures not just that replicas hold the same data, but in the same order, under the same history. This requires more than copying data between nodes. It requires coordination. It requires leadership. In consensus protocols like Raft,…
In my last blog, we looked at how the Write-Ahead Log (WAL) underpins durability across different replication designs. But it’s equally important to understand why, in the world of consensus, the same idea is called a replicated log instead. A Write-Ahead Log (WAL) remembers what happened locally. A replicated…
In distributed systems, it’s easy to blur the line between keeping data safe and keeping data in order. Both sound like the same thing, until you look closely at how systems actually do it. At the centre of this confusion lies a familiar piece of technology: the log. Specifically,…
Quorum and Consensus appear frequently in distributed-systems literature – especially in discussions around replication, fault tolerance and distributed databases. They often sound like close cousins, both involve replicas "agreeing" on something, both rely on majorities, and both aim to keep a distributed system from drifting apart. Yet, despite these…
Software systems are built on layers of abstractions. Each layer shields developers from the messy realities beneath, allowing them to think in simpler, more reliable terms. One of the most powerful examples of this principle comes from databases called Transactions. Transactions embody the ACID guarantees — Atomicity, Consistency, Isolation, and Durability…