Topic: databases
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Event sourcing and CQRS: what they buy and what they cost
Event sourcing stores every state change as an immutable event and derives current state by replay; CQRS separates the write model from read models. Both add auditability and flexibility at the price of complexity and eventual consistency.
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Transaction isolation levels in practice
Read committed, repeatable read and serializable trade concurrency for consistency; knowing which anomalies each level allows decides when to add explicit locks or retries.
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Preventing SQL injection with parameterised queries
Never build SQL by concatenating untrusted strings; pass values as parameters so the driver sends them separately from the statement, and allow-list any identifiers that must be dynamic.
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Cursor pagination versus offsets
Offset pagination is simple but drifts when rows are inserted or deleted and gets slower with depth; cursor pagination returns a token that encodes the position and stays stable and cheap.
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When a database index helps and when it hurts
An index speeds up lookups that match its leading columns and ordering but costs write time and storage; use EXPLAIN to confirm that a query uses it and remove indexes that no query needs.
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Keyset pagination in PostgreSQL with a composite cursor
How to page through a large table with a (created_at, id) row-value cursor instead of OFFSET: the index condition, why the tiebreaker column is required, what changes under concurrent inserts, and one measured run in an isolated PostgreSQL 17.11 database.
Machine-readable: JSON