# Read your writes

> After a user writes, send that user's reads to the primary for a while, so they never see data older than their own change.

Read-your-writes guarantees that a user who just saved something sees it on the next page.

## Use it when

- Reads go to replicas that lag the primary, and users edit something they then view.
- A checkout or a settings page reads back what it just wrote.
- Stale answers from other users' writes are fine, but your own are not.

## How it works

The app notes when a user last wrote, and for a short window after it sends that user's reads to the primary. A common window is a few seconds, longer than the usual replica lag. Other reads go to replicas as before. Another way is to carry the log position of the write and read only from a replica that has reached it.

If a user saves a profile and 200 ms later reloads, a lagging replica may return the old one. With the rule, the reload goes to the primary and shows the new one.

## What it costs

Reads after a write land on the primary, so a write-heavy user adds load there. The rule works per user or session and does not stop one user seeing another's older data. It also needs a clock or a position the app can trust, and a user on two devices has two sessions. Windows that are too short still show stale data.

## In Quorum



The routing switch sits on the [App Server](https://wiki.playquorum.dev/components/server.md). With it on, checkout reads go to the primary and never come back stale, and most other stale reads go away. It needs [Read-your-writes routing](https://wiki.playquorum.dev/research/ryw-routing.md) after [Read replicas](https://wiki.playquorum.dev/research/replication.md).

It makes the [Replication lag](https://wiki.playquorum.dev/incidents/repl-lag.md) incident much rarer, and the [Stale read](https://wiki.playquorum.dev/incidents/stale-read.md) incident lists it as one fix. A [Synchronous replica](https://wiki.playquorum.dev/patterns/replication-strategies.md) is the costlier fix. The glossary defines [read-your-writes consistency](https://wiki.playquorum.dev/glossary/read-your-writes-consistency.md).

Source: https://wiki.playquorum.dev/patterns/read-your-writes