The replica’s I/O thread lost its network connection while reading binary log events from the primary server.
MySQL Error 1189: ER_MASTER_NET_READ occurs when a replica cannot read data from the primary due to a network interruption or resource limit. Fix it by checking network stability, increasing replication timeouts, and validating that max_allowed_packet and net_read_timeout are large enough on both servers.
ER_MASTER_NET_READ
The error appears in replicas as "Error 1189: ER_MASTER_NET_READ (08S01) - Net error reading from master." It signals that the replica’s I/O thread failed to read a chunk of the binary log sent by the primary.
MySQL treats this as a network failure. Replication stops or retries, risking lag and data inconsistency if not resolved quickly.
Most incidents stem from unstable or saturated network links between the primary and replica.
Packets drop, TCP connections reset, and the I/O thread aborts.
Large binary log events can exceed max_allowed_packet or time out during transfer if net_read_timeout is too small, producing the same error.
First confirm network reachability with ping and traceroute.
If connectivity is poor, move servers to the same zone or upgrade bandwidth.
Next, raise net_read_timeout and slave_net_timeout on the replica, and increase max_allowed_packet on both servers to fit the largest binlog event.
Cloud VMs in different regions often drop long-running connections. Deploy a VPN or private link to stabilise traffic.
High-volume bulk inserts create huge binlog rows.
Enable row compression or split transactions to shrink event size.
Keep primaries and replicas in the same availability zone.
Monitor replication delay with SHOW SLAVE STATUS and alert on growing Seconds_Behind_Master.
Schedule binlog purges but retain enough history to allow replicas to reconnect after transient failures.
Error 1158 (ER_NET_READ_ERROR) appears during client reads, not replication, but the troubleshooting steps overlap: check network and timeouts.
Error 1593 (ER_SLAVE_GTID_MISMATCH) indicates GTID conflicts rather than connectivity. Fix by skipping or aligning transactions.
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Yes. The I/O thread halts until you issue START SLAVE after resolving the network or configuration issue.
Short, self-healing outages may auto-retry, but frequent occurrences increase replication lag. Investigate root causes.
net_read_timeout, slave_net_timeout, and max_allowed_packet directly influence the likelihood of this error.
Galaxy’s editor surfaces replication status queries and lets you save them as endorsed checks, making monitoring easy and collaborative.
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