GuideTechnology
35 min read
Add interviews to job applications and meet the real problems of JPA: relationship mapping, lazy loading and its exception, the N+1 query problem measured and fixed, what @Transactional does and does not do, and optimistic locking that stops lost updates, all tested on PostgreSQL.
GuideTechnology
21 min read
Learn the SQL that backend developers use every day on PostgreSQL: tables and constraints, inserting, querying, joining and grouping data, transactions and isolation, indexes and query plans, and normalisation, with every statement run on a real PostgreSQL server.
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
How to keep data consistent when one business action spans a database and a message broker, or several services. Covers the dual-write problem, the transactional outbox and change data capture, two-phase commit and why it blocks, and sagas with compensating transactions, choreography versus orchestration, pivot steps and isolation anomalies, with a runnable saga.
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.
GuideTechnology
17 min read
How to model data for a system design: tables, primary and foreign keys, constraints, one-to-many and many-to-many relationships, normalisation and deliberate denormalisation, ACID transactions, choosing id formats, and designing the model around access patterns. Also covers connection pooling, the N+1 problem and safe schema changes.
