GuideTechnology
16 min read
Design ticketing for concerts and matches where thousands of people want the same seats at the same moment: seat inventory modelling, holds with expiry, atomic all-or-nothing seat claims, idempotent payment and confirmation, what happens when payment succeeds after a hold expires, virtual waiting rooms for big on-sales, hot inventory, bots, failures and the invariant that a seat is never sold twice.
GuideTechnology
16 min read
When only one node may do something at a time: when you actually need a distributed lock and when you do not, locks for efficiency versus correctness, leases and why they need fencing tokens, Redis and database locks and their limits, leader election, and consensus (Raft, majorities, ZooKeeper and etcd) explained at interview depth.
GuideTechnology
15 min read
What "consistent" means when data is replicated, from linearizability through causal and session guarantees to eventual consistency; what the CAP theorem actually says and why "pick two" misleads; PACELC and the everyday latency trade-off; quorum reads and writes; resolving conflicts; and choosing consistency per feature instead of per system.
GuideTechnology
14 min read
What changes when work is spread over many machines: partial failure, messages that are lost, delayed, duplicated or reordered, timeouts with unknown outcomes, process pauses, and clocks that disagree. Learn why a timeout does not tell you what happened, why wall clocks cannot order events, how logical clocks help, and the design habits that follow.
GuideTechnology
15 min read
Why databases keep copies on several machines, and what those copies cost. Covers primary-replica replication, synchronous versus asynchronous replication, read replicas for scaling, replication lag and the read anomalies it causes, read-your-writes routing, failover and split brain, multi-leader and leaderless replication, and why replication is not a backup.
GuideTechnology
16 min read
What goes wrong when many requests touch the same rows at once: lost updates, double booking, write skew, dirty and non-repeatable reads. Learn isolation levels, MVCC, atomic conditional updates, row locks, optimistic concurrency with versions, constraints, deadlocks and hot rows, with a runnable simulation and worked examples.
GuideLife
6 min read
Most habit plans fail in the second week because they depend on motivation. Here is a practical method: start tiny, anchor the habit to your day, design your environment, track it and plan for slips.
