This article walks through a systematic analysis of MySQL slow‑log entries, correlating them with error‑log flush events, disk‑I/O monitoring, and semi‑synchronous replication traces to pinpoint performance bottlenecks and provide practical troubleshooting steps.
This article explains the principles of MySQL semi‑synchronous replication, analyzes how data consistency is maintained during high‑availability failover, presents detailed step‑by‑step transaction flow, discusses scenarios causing GTID divergence, and offers testing methods and remediation techniques for DBA practitioners.
This article documents a reproducible test that shows gh-ost can lose rows when used on a MySQL 5.7 AFTER_SYNC semi‑synchronous replica, explains the underlying cause, and presents a source‑code modification that prevents the loss.
An in‑depth investigation reveals that when MySQL semi‑sync replication is configured with rpl_semi_sync_master_wait_for_slave_count=1, starting a second slave can cause the master’s dump thread to fail, leading to slave_io_thread stalls; the analysis includes reproduction steps, status checks, thread stack traces, and a patch using sched_yield to resolve the lock contention.
A performance test using sysbench on a dual‑node DL380 G7 MySQL 5.6 cluster shows that semi‑synchronous replication delivers roughly one‑third the TPS of asynchronous replication and highlights recovery and replication‑lag limitations that can be mitigated with sharding and parallel workers.
