# Split the database by feature

> Give each feature its own App Server and Database, so one feature's load and failures stay in its own lane.

Route each feature to its own servers and its own Database, so the browse load cannot slow the orders.

## Move up when

- One table or one feature takes most of the primary's load, and a slow report or search there slows checkouts.
- Teams step on each other because they share one schema and one deploy.
- You want to size, tune, and fail one feature without touching the others.

## The Design



The game has no way to split one Database by table. This Design draws the idea with two Databases behind two App Servers. A Load Balancer sends each request kind down a different Link, which stands for routing by feature. The browse side takes pages and reads, and the orders side takes writes and checkouts. Each App Server calls its own Database, and only orders reaches the Payment Provider.

## Why it works

Each Database holds less, so its cache fits its own hot rows and its load bar tracks one feature. A failure in one lane leaves the other serving. You can also give the orders Database a stronger setup than the catalog one.

## What it costs

A query that joins across the split no longer works. The app has to call both sides and merge, and a change touching both is no longer one transaction. Each Database is a Node to run and pay for. Moving a table later is a data migration, so choose the seams along ownership, not along tables.

## In Quorum

Draw it as above, with one Link setting that carries only some request kinds from a [Load Balancer](https://wiki.playquorum.dev/components/lb.md). Separate codebases and teams come with [Service boundaries](https://wiki.playquorum.dev/research/service-boundaries.md). The pattern is on [Federation](https://wiki.playquorum.dev/patterns/federation.md), and the opposite move, spreading one table, is [Sharding](https://wiki.playquorum.dev/patterns/sharding.md). The next rung moves slow work off the request: [Slow work to a queue and workers](https://wiki.playquorum.dev/patterns/slow-work-to-a-queue-and-workers.md).

Source: https://wiki.playquorum.dev/patterns/split-the-database-by-feature