How to improve MySQL performance by using semi-synchronous replication

With the continuous development of the Internet, the explosive growth of data volume has made databases become the core components of many websites, applications and systems. As an open source relational database management system, MySQL has become the preferred database widely used in the industry due to its advantages in stability, reliability and cost-effectiveness.

However, in the actual production environment, as the amount of data increases, MySQL's performance problems are gradually exposed. Especially in large-scale enterprise applications, the reading and writing of massive data, high concurrent requests, and data reliability all place high demands on MySQL's performance.

In order to meet these needs, MySQL provides the semi-synchronous replication (Semi-Synchronous Replication, referred to as Semi-Sync) function. By using semi-synchronous replication, the performance and reliability of MySQL can be improved. This article will introduce the principles, advantages and usage of semi-synchronous replication.

1. The principle of semi-synchronous replication

MySQL replication refers to the process of synchronizing data from one MySQL instance (Master) to another MySQL instance (Slave). When a transaction is executed on the Master, it will be written to the Master's binlog and transmitted to the Slave through the network for execution.

Semi-synchronous replication is based on ordinary asynchronous replication and adds an additional synchronous confirmation process. When a transaction is executed on the Master and successfully written to the Master's binlog, the Master will wait for at least one Slave to confirm that the transaction has been successfully written to its corresponding relay log. Only after receiving confirmation from at least one Slave, the Master will consider that the transaction has been successfully copied to the Slave, and then notify the client that the transaction has been submitted.

In semi-synchronous replication, Master and Slave interact through the network. When a transaction on the Master is completed, the Master will send a transaction confirmation request to all connected Slaves and wait for at least one Slave to respond to the request. If the waiting time exceeds the set timeout, the Master will give up waiting.

2. Advantages of semi-synchronous replication

Compared with ordinary asynchronous replication, semi-synchronous replication has the following advantages:

1. Improving the reliability of data

In ordinary asynchronous replication, since the Slave executes transactions on the Master asynchronously, there may be data loss. For example, when the Master is writing a transaction, the Master crashes or other abnormal conditions cause the transaction not to be written to the binlog. At this time, even if the transaction is executed, the binlog of the transaction does not exist on the Slave. resulting in data loss.

In semi-synchronous replication, after receiving the transaction confirmation request from the Master, the Slave will immediately write the transaction to its own relay log. Only when the slave writes successfully, the master will consider that the transaction has been successfully copied to the slave, thereby ensuring the reliability of the data.

2. Improve read performance

In ordinary asynchronous replication, due to the delay in the asynchronous transmission of data between Master and Slave, and the delay time of each Slave may are different, so the data read on the Slave may be out of date.

In semi-synchronous replication, when the Master receives a response from at least one Slave, it will consider that the transaction has been copied to the Slave and submitted. At this time, reading the data on the Slave is more reliable, thereby improving improve read performance.

3. Enhance load balancing capabilities

Semi-synchronous replication can improve load balancing capabilities. In semi-synchronous replication, due to the read-write separation strategy, some requests only need to be performed on the Slave, which reduces the Master's read operations, thus greatly reducing the Master's read burden. At the same time, when the Master performs a write operation and waits for a response from at least one Slave, the network IO can be utilized, which means that network resources are fully utilized.

3. How to use semi-synchronous replication

Semi-synchronous replication is available starting from MySQL 5.5.9 and requires corresponding configuration on the Master and Slave. The following is the specific configuration method.

Configuration on the Master:

1. First, you need to ensure that all connected Slaves support Semi-Sync. Use the show slave statusG command to check the support status of the currently connected Slave.
2. Enable the semi-synchronous replication function and set the parameter to "1". The setting method is as follows:

mysql> SET GLOBAL rpl_semi_sync_master_enabled = 1;

3. Set the number of Slaves required to meet semi-synchronous replication. Set the parameter to "1" or "2", indicating that at least 1 or 2 Slave is required for confirmation. Here we take the setting that requires at least 1 Slave confirmation as an example.

mysql> SET GLOBAL rpl_semi_sync_master_wait_for_slave_count = 1;

Configuration on Slave:

1. Enable the semi-synchronous replication function and set its status to "ON". The setting method is as follows:

mysql> SET GLOBAL rpl_semi_sync_slave_enabled = ON;

2. Set Slave as an intermediary to handle communication between Master and other Slaves. The setting method is as follows:

mysql> CHANGE MASTER TO MASTER_HOST='xxxx', MASTER_PORT=3306, MASTER_USER='user', MASTER_PASSWORD='password', MASTER_USE_SEMI_SYNC = SLAVE;

You need to replace "xxxx", "user", and "password" with the actual Master's IP address, username, and password.

After the configuration is completed, you can check the status of semi-synchronous replication through the following command:

mysql> SHOW GLOBAL STATUS LIKE 'Rpl_semi%';

Among them, the value of Rpl_semi_sync_master_status is ON, which means that the Master has turned on the semi-synchronous replication function, and the value of Rpl_semi_sync_slave_status If it is ON, it means that the slave has turned on the semi-synchronous replication function.

4. Summary

By using semi-synchronous replication, the performance and reliability of MySQL can be improved. Therefore, in actual production environments, we should use semi-synchronous replication technology as much as possible to ensure data reliability and improve MySQL's read and write performance. At the same time, when using semi-synchronous replication technology, you also need to pay attention to the details of the configuration file to ensure its correctness.

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