Tag

databases

11 cards

Cards

A 2TB table moving onto four shards with no downtime through dual write, backfill, verify, gradual read shift and finish, set against the naive stop-and-copy plan

DatabasesDay 46Sep 17, 2026

Splitting a Table While People Are Using It

system-design databases sharding

A column rename breaking during a rolling deploy while both code versions are live, and the expand-migrate-contract sequence that makes each step safe alone and reversible

DatabasesDay 45Sep 16, 2026

Never Change Anything in One Step

system-design databases migrations

B-tree, GIN, BRIN, partial and covering indexes compared by the question each one answers, and a billion-row table where BRIN costs 300 KB against a B-tree's 5 GB

DatabasesDay 44Sep 15, 2026

Not Every Index Is a Tree

system-design databases indexes

Why every Postgres connection is a separate OS process costing megabytes, how 500 connections on 16 cores collapses throughput, where the queue forms under a small pool versus a large one, and a pooler as the fix

DatabasesDay 43Sep 14, 2026

A Connection Costs More Than You Think

system-design databases connection-pooling

Index lookup against sequential scan for the same query, the row-count threshold where the planner switches, three ways statistics mislead it, and ANALYZE before reaching for a new index

DatabasesDay 42Sep 12, 2026

Why It Ignored Your Index

system-design databases query-planner

The write-ahead log ordering — transaction, append to WAL, fsync, modify in memory, flush data pages later — with crash recovery replaying committed changes, and the same log driving replication, PITR and audit

DatabasesDay 41Sep 10, 2026

Write It Down Before You Do It

system-design databases write-ahead-log

How an insert, update and delete leave live and dead row versions in the same Postgres table, the bloat after a million rows updated ten times each, and VACUUM marking dead space reusable

DatabasesDay 40Sep 9, 2026

Your Database Doesn't Delete Anything

system-design databases mvcc

B-tree versus LSM tree — updating a page in place against appending to a memtable and flushing to sorted files, with compaction as the hidden cost

Storage EnginesDay 28Aug 28, 2026

Two Ways To Write A Number Down

system-design storage-engines databases

You Posted It. Then It Vanished. — system design card, day 20, databases

DatabasesDay 20Aug 20, 2026

You Posted It. Then It Vanished.

databases postgresql system-design

The Index You Added Made Writes Slower — system design card, day 18, databases

DatabasesDay 18Aug 18, 2026

The Index You Added Made Writes Slower

databases postgresql system-design

The Bug That Passes Every Test — system design card, day 6, databases

DatabasesDay 6Aug 6, 2026

The Bug That Passes Every Test

databases postgresql system-design