MySQL cannot write binary log events across the network to a replica, breaking replication and returning ER_MASTER_NET_WRITE (SQLSTATE 08S01).
MySQL Error 1190: ER_MASTER_NET_WRITE happens when the master server fails to send binary-log data to a replica because the network write times out or drops. Check network latency, raise net_write_timeout, and restart replication with START SLAVE to restore syncing.
Net error writing to master
MySQL throws ER_MASTER_NET_WRITE (error 1190, SQLSTATE 08S01) when the source instance tries to stream binary-log events to a replica but cannot finish the network write. The replication I/O thread on the replica closes the connection, replication stops, and SHOW SLAVE STATUS reports the error.
Because replication halts, transactions committed on the source never reach downstream replicas, risking data drift and stale reads.
Production workloads that rely on read replicas may face inconsistent results until the issue is fixed.
The error surfaces during asynchronous or semisynchronous replication on MySQL 5.5 and newer. It is logged on the master if the write fails, and on the replica as “I/O error reading from master” immediately afterward.
It often follows network interruptions, high latency, or overloaded servers that exceed net_write_timeout.
Unresolved replication gaps grow over time, forcing expensive full re-syncs or causing irreversible data divergence. Fast remediation preserves data integrity, keeps replicas usable for failover, and avoids unplanned downtime.
Most cases trace back to unstable network links between master and replica.
Packet loss, firewall drops, or VPN flaps interrupt the TCP stream, so the master cannot flush binlog data.
Large transactions or long-running bulk inserts can exceed net_write_timeout or slave_net_timeout, leading to timeouts even on healthy links.
Resource saturation on the master, such as high CPU or disk I/O, slows binlog flushing and delays network writes until the connection times out.
Version or parameter mismatches, including disabled binary logging, semisync plugin bugs, or incompatible TLS settings, occasionally trigger the write failure.
First verify connectivity: ping, traceroute, and MySQL client logins from the replica to the master.
Fix any network instability or firewall rules blocking port 3306.
Review net_write_timeout (master) and slave_net_timeout (replica). Temporarily raise both to 120 or 300 seconds, then retry replication. Longer timeouts tolerate latency spikes.
Restart replication cleanly: on the replica execute STOP SLAVE; START SLAVE;.
Check SHOW SLAVE STATUS until Seconds_Behind_Master drops and Last_IO_Errno becomes 0.
If logs show a large transaction near the failure time, split the transaction or enable binlog_row_image = MINIMAL to shrink event payloads.
Cloud region link outage – Wait for the provider to restore connectivity, then START SLAVE or CHANGE MASTER TO MASTER_AUTO_POSITION=1 to resume GTID-based replication.
Bulk load exceeding timeout – Increase net_write_timeout to 300 and split the load into smaller batches.
Overloaded master – Tune innodb_flush_log_at_trx_commit, sync_binlog, or add IOPS.
Offload heavy reads to replicas via Galaxy’s query routing to reduce master stress.
Place replicas in the same availability zone or use dedicated replication links to minimize latency and packet loss.
Monitor Round-Trip Time, Seconds_Behind_Master, and Replica_IO_Running with Prometheus or MySQL Enterprise Monitor.
Alert on spikes before timeouts occur.
Set net_write_timeout, net_read_timeout, and slave_net_timeout to balanced values (60-120s) based on workload latency.
Enable GTID replication so replicas can auto-position after transient disconnects without manual log-file bookkeeping.
Error 1158 ER_NET_READ_ERROR_FROM_PIPE – Read failure instead of write; fix network or increase net_read_timeout.
Error 1159 ER_NET_FCNTL_ERROR – Socket control failure; check OS ulimit and open-files count.
Error 1236 ER_MASTER_FATAL_ERROR_READING_BINLOG – Replica cannot parse binlog; ensure identical MySQL versions or upgrade.
Error 1593 ER_IO_THREAD_SHUTDOWN_COMPLETE – I/O thread stopped after repeated write errors; restart replication.
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No. It only extends how long MySQL waits before declaring the network write failed. Transactions remain durable.
Do not ignore it. Each occurrence pauses replication. Frequent gaps can mask data divergence and break failover plans.
Semi-sync still uses the same socket. The error can occur; however, ACK monitoring may detect delays sooner.
Galaxy’s SQL editor quickly surfaces SHOW SLAVE STATUS output, shares remediation queries, and stores endorsed runbooks so teams can respond faster.
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