In MariaDB, master-slave delay in strong synchronization (also called "semi-synchronous replication") can occur due to several reasons:
Network Latency: If the network between the master and slave is slow or congested, the acknowledgment (ACK) from the slave to the master may be delayed, causing the master to wait before committing transactions.
Slave Performance Issues: If the slave server is under heavy load, has insufficient resources (CPU, I/O, memory), or is processing other heavy queries, it may take longer to apply the replicated transactions, leading to delay.
Large Transactions: If the master commits large transactions (e.g., bulk inserts or updates), the slave may take more time to apply them, increasing the delay.
Semi-Synchronous Replication Overhead: In semi-synchronous replication, the master waits for at least one slave to acknowledge receipt of the transaction before committing. If the slave is slow to respond, the master's commit process is delayed.
Suppose a MariaDB master receives a large batch insert (e.g., 1 million rows). The master sends the data to the slave but waits for an ACK before committing. If the slave is slow due to high CPU usage or network issues, the master will stall, causing a delay in strong synchronization.
To mitigate master-slave delay, Tencent Cloud provides TencentDB for MariaDB, which offers optimized replication mechanisms, automatic failover, and performance monitoring. Features like read/write separation and automatic load balancing can help reduce slave lag by distributing read queries efficiently. Additionally, TencentDB's enhanced monitoring helps identify performance bottlenecks, allowing quick troubleshooting.