Dungeons & Databases Split the Realm
All 08 lessons unlocked

A guided path · nine lessons

The journey of one database, from its first slow query to its last shard.

The realm is your database and everything depending on it. Splitting it — across tables, then across machines — is the last and most expensive thing you can do to it.

You will learn where a database actually spends its time, what an index, a partition, a shard, and a replica each buy — and what every one of them costs.

Enter the first vault See the path
8
guided lessons
1
bonus lesson
1
evolving database
Where the story begins Under pressure
Request sourceClients
ApplicationOrders API
One growing tableOrders Vault
Working set 118% of memory

The Old Dragon speaks

“A crowded vault and a broken vault are not the same thing.”

The scribes want twelve partitions before they have measured one bottleneck. Walk with me through the machinery beneath their tables. We will split nothing until we know what the split is meant to solve.

The Old Dragon, keeper of the deep ledger

Every lesson adds one justified decision.

We begin with symptoms, descend into database internals, and return with enough knowledge to choose between an index, a partition, a shard, and a replica.

  1. 01 Unlocked The first warning The Groaning Vault Diagnose why the database is slow before choosing a remedy. BottlenecksBaselinePressure Explore lesson
  2. 02 Unlocked Inside the machine Beneath the Vault See pages, the buffer pool, eviction, and the working-set cliff. PagesMemoryI/O Explore lesson
  3. 03 Unlocked Where, not just what The Dragon’s Power Turn a hundred disk trips into two, and finally make memory work. IndexesB-treesAccess paths Explore lesson
  4. 04 Unlocked The bill arrives The Dragon’s Debt Follow a write through the log, and count what every extra index costs. WALDirty pagesAmplification Explore lesson
  5. 05 Unlocked Boundaries within Divide the Hoard Prune whole regions of history and respect the one-machine ceiling. PruningRetentionCeilings Explore lesson
  6. 06 Unlocked Beyond one keep Across Many Keeps Route data across machines and choose a shard key that survives growth. RoutingFan-outRebalancing Explore lesson
  7. 07 Unlocked Copy for reads Copies of the Ledger Add read capacity with the same log, then face lag and stale answers. WAL shippingLagFailover Explore lesson
  8. 08 Unlocked The hidden bill The Price of Many Realms Choose consistency per operation and compare every scaling tool. IsolationIdempotencySagas Explore lesson
  9. 09 Bonus Advanced The Keeper’s Judgement All eight lessons in one place, and which technique a real problem actually calls for. RecapTriageOrder of work Explore lesson
“When you leave this realm, you will not ask how to shard first. You will ask what has run out, and know which tool earns the right to fix it.”
The Old Dragon