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
15 min read
A trade-off-driven guide to choosing databases: relational, key-value, document, wide-column, graph, search, time-series and analytical stores, what each is good and bad at, query-first modelling for NoSQL, the myths ("NoSQL scales, SQL doesn't"), polyglot persistence, and a decision process you can use in interviews.
GuideTechnology
17 min read
When one database can no longer hold the data or absorb the writes, you split it. Learn vertical and horizontal partitioning, how to choose a partition key, range, hash, consistent-hashing and directory-based sharding, rebalancing with logical shards, hot partitions, cross-shard queries and secondary indexes, and why you should shard as late as possible.
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.
GuideTechnology
15 min read
Why a query over millions of rows can take seconds or milliseconds depending on one index. Learn how B-tree indexes work, why they stay shallow, composite index column order, covering and partial indexes, selectivity, reading a query plan at a high level, why indexes are sometimes ignored, and what every index costs on writes.
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.
