EC
1658
MariaDBERRORCommonReplicationHIGH confidence

Replica configuration error

Production Risk

High — replica will not replicate until correctly configured.

What this means

The replica cannot start because its configuration is invalid or incomplete (e.g., missing source host, missing relay log configuration).

Why it happens
  1. 1CHANGE MASTER TO was not executed before START SLAVE.
  2. 2Required replication parameters (host, port, user, password) are missing.
  3. 3The relay log directory is unavailable or not configured.
How to reproduce
trigger — this will error
trigger — this will error
START SLAVE;
-- Without first running CHANGE MASTER TO ...

expected output

ERROR 1658 (HY000): Replica configuration error: master_host is not set.

Fix

Configure the replication source before starting

Configure the replication source before starting
CHANGE MASTER TO
  MASTER_HOST='primary.example.com',
  MASTER_PORT=3306,
  MASTER_USER='replicator',
  MASTER_PASSWORD='secret',
  MASTER_AUTO_POSITION=1;
START SLAVE;

Why this works

Providing all required source parameters allows the replica to connect.

Version notes

Sources
Official documentation ↗

MySQL 8.0 — 1658 ER_SLAVE_CONFIGURATION

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