Answer
Lag occurs when replicas apply changes slower than the primary. Use Seconds_Behind_Master and check slow queries or overloaded replica hardware.
Quick Answer
Replication lag causes: replica hardware slower than primary, large transactions (single big transaction blocks replica for its full duration), missing indexes on replica (applies DML slower), insufficient replica I/O or SQL threads. Detect: SHOW SLAVE STATUS shows Seconds_Behind_Master. Monitor with Prometheus + replication exporter. Fix: optimize slow queries on replica, use parallel replication (slave_parallel_workers).
S
SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ