---
title: "Read from replicas only what may lag · Agent Wranglers"
url: https://agentwranglers.se/playbook/data/caches-and-copies/replica-lag
updated: 2026-10-20
licence: "All rights reserved"
---

# Read from replicas only what may lag

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Recommended
- Chapter: [Caches and copies](https://agentwranglers.se/playbook/data/caches-and-copies)
- Rule: Send reads to a replica only when a few seconds of delay is acceptable. Read your own writes from the primary.
- How: After a user changes something, read it back from the primary for that user, or wait until the replica has caught up. Monitor replica lag and stop routing reads to a replica that falls behind.
- Check: A test saves a change and reads it back at once, 100 times in a row, while replica lag is simulated. Every read shows the change.

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers data playbook: https://agentwranglers.se/playbook/data/caches-and-copies/replica-lag`.

- Previous: [Decide how stale a cache may be](https://agentwranglers.se/playbook/data/caches-and-copies/cache-freshness)
- Next: [Keep search indexes in step](https://agentwranglers.se/playbook/data/caches-and-copies/search-index-sync)
- [Caches and copies](https://agentwranglers.se/playbook/data/caches-and-copies)