InnoDB Adaptive Hash Index Contention
infoContention on InnoDB adaptive hash index causing performance degradation. Multiple threads compete for AHI mutex access, reducing query throughput. Common in high-concurrency workloads with point lookups on frequently accessed indexes.
mysql.innodb.hash_index_cells_used / mysql.innodb.hash_index_cells_total > 0.95, or mutex contention in SHOW ENGINE INNODB STATUS semaphores section showing high AHI wait times
Review adaptive hash index usage in SHOW ENGINE INNODB STATUS output. For MySQL 5.7+, consider disabling AHI on specific partitions or globally (innodb_adaptive_hash_index=OFF) if contention is severe and point lookup performance is not critical. Monitor mysql.performance.cpu_time - if CPU is high with low query throughput, AHI contention may be culprit. In MySQL 8.0+, AHI is partitioned by default, reducing contention. Check innodb_adaptive_hash_index_parts setting. Evaluate workload: AHI benefits point lookups but adds overhead for range scans and updates.