Glossary

Resistance or force opposing the desired flow of data through a system. Used to slow down producers when consumers cannot keep up, preventing queue overflow.

In a distributed system, you can provide at most two of three guarantees: Consistency, Availability, Partition tolerance. Under network partition, you must choose between C and A.

A caching strategy where the application checks the cache first; on a miss, it fetches from the source, writes to the cache, and returns. The cache is not pre-populated.

A geographically distributed network of proxy servers that serves cached content to users from the nearest edge location, reducing latency and origin load.

A reliability pattern that stops calling a failing downstream service after a threshold of failures, allowing it to recover. Trips 'open', then periodically tests 'half-open'.

A hierarchical, decentralized naming system that translates human-readable domain names (example.com) into IP addresses (93.184.216.34).

A consistency model where, given no new updates, all replicas will eventually converge to the same value. Reads may return stale data in the interim.

A property of an operation where executing it once has the same effect as executing it multiple times. Critical for safe retries in distributed systems.

A component that distributes incoming requests across multiple servers to maximize throughput, minimize response time, and avoid overload on any single server.

The time taken for a request to travel from source to destination and back. Measured in milliseconds. p95 and p99 latency are common SLOs.

A software architectural pattern that separates application logic into three interconnected components: Model (data), View (UI), Controller (input).

An architectural style where an application is composed of small, independently-deployable services that communicate over a network. Opposite of monolith.

The minimum number of nodes in a distributed system that must agree on a value for it to be accepted. Typically a majority (N/2 + 1) to tolerate minority failures.

Copying data from a primary database to one or more replica databases to improve read availability, scalability, and fault tolerance.

A component in a system whose failure causes the entire system to fail. Architecture review identifies and eliminates SPOFs through redundancy.

Splitting a large database into smaller, horizontally-partitioned pieces (shards) distributed across multiple servers. Each shard holds a subset of rows.

A consistency model where all reads see the most recent write, as if there were a single copy of the data. Requires coordination, reducing availability under partition.

The rate at which a system processes requests or data, typically measured in requests per second (RPS) or bytes per second.