Concepts·MySQL
MySQL Replication Topology Monitoring
SHOW REPLICA STATUS says replication is running. It cannot say the data matches - and the replication track proved those are different questions. A checksum across all three hosts is the check that closes the gap.
Monitoring and Operations Guide 45 of 45 Advanced
- OSUbuntu 26.04 LTS
- MySQL8.4.10-0ubuntu0.26.04.1
- Topologydb-a01 source, db-b01 and db-c01 replicas
- TimeAbout 14 min
pt-table-checksum from Percona Toolkit does this properly at scale, chunking large tables and comparing under load. The query here is the same idea, small enough to read.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| db-a01 | 192.168.0.81 | Ubuntu 26.04 LTS | Primary / Source / Replica Set Member 1 | 2 Core | 4 GB | 50 GB |
| db-b01 | 192.168.0.82 | Ubuntu 26.04 LTS | Standby / Replica / Replica Set Member 2 | 2 Core | 4 GB | 50 GB |
| db-c01 | 192.168.0.83 | Ubuntu 26.04 LTS | Replica Set Member 3 / Cascading and Delayed Replica | 2 Core | 4 GB | 50 GB |
This guide includes
Use this when replication reports healthy and you would like to believe it. This matters because SHOW REPLICA STATUS tells you the threads are running - it cannot tell you the data matches.
- checking the four fields that say replication is running, on both replicas
- checking that the data actually matches, which status cannot do
- seeing why the second check is the one that matters
Before you start
- A running topology - see the replication track.
- The same table present on every host.
-
Check that replication is running
-
Check that the data actually matches