Configuring the Delay Threshold and Routing Policy

Constraints

To enable proxy load balancing, contact customer service.

All proxies of your DB instance must be in the Available state.

Configuring Delay Threshold

1. Log in to the management console.
2. Click in the upper left corner and select a region.
3. Click in the upper left corner of the page and choose Databases > Relational Database Service.
4. On the Instances page, click the primary instance name.
5. In the navigation pane on the left, click Database Proxy.
6. In the proxy information area, click next to the Delay Threshold field.

Configuring Routing Policy in Single-Proxy Mode

1. Log in to the management console.
2. Click in the upper left corner and select a region.
3. Click in the upper left corner of the page and choose Databases > Relational Database Service.
4. On the Instances page, click the primary instance name.
5. In the navigation pane on the left, click Database Proxy.
6. If proxy load balancing is not enabled, click Configure next to the Routing Policy field in the proxy information area. In the displayed dialog box, configure read weights for the primary instance and read replicas.
   

   • The system automatically distributes weights to read replicas, including read replicas created afterwards, according to the default distribution rules. If a read replica breaks down or is deleted, the weight is automatically removed. After the read replica recovers, the weight is automatically restored.
   • If the weight of a node is set to 0, read requests will not be routed to the node. If the weights of all nodes are set to 0, read requests will be randomly routed to these nodes.
   • Forcible routing is also supported. For details, see Adding a Hint to Specify the Direction that a SQL Statement Will Be Routed.
   Figure 1 Setting read weight
   

7. Click OK and view the weights on the Database Proxy page.
8. If proxy load balancing is enabled, click Configure next to the Routing Policy field in the proxy information area. In the displayed dialog box, set required parameters.

   Select Load balancing as the routing policy. Read requests will be automatically distributed to read replicas based on the number of active connections to balance the load among these read replicas.

   Figure 2 Routing policy - Load balancing
   
   Read Requests Accepted by Primary DB Instance:

   • Yes: Read requests can be routed to both the primary instance and read replicas, which increases the load of the primary instance. Configure this parameter as required.
   • No: To offload read pressure from the primary instance, read requests are only routed to read replicas.

9. Click OK. On the Database Proxy page, view the result. You can select the instances for load balancing as required.

Configuring Routing Policy in Multi-Proxy Mode

1. Log in to the management console.
2. Click in the upper left corner and select a region.
3. Click in the upper left corner of the page and choose Databases > Relational Database Service.
4. On the Instances page, click the primary instance name.
5. In the navigation pane on the left, click Database Proxy.
6. In the proxy information area, click Configure next to the Routing Policy field. In the displayed dialog box, set required parameters.
   • Weighted: You can distribute read weights for the DB instance and read replicas. For details, see Table 1.
     

     The system automatically distributes weights to read replicas, including read replicas created afterwards, according to the default distribution rules. If a read replica breaks down or is deleted, the weight is automatically removed. After the read replica recovers, the weight is automatically restored.

     Forcible routing is also supported. For details, see Adding a Hint to Specify the Direction that a SQL Statement Will Be Routed.

     Figure 3 Weighted
     
     Click OK and view the weights in the proxy information area.

     Figure 4 Viewing weights
     
   • Load balancing: If selected, to balance the load among read replicas, read requests are automatically distributed to multiple read replicas based on the number of active connections.
     Figure 5 Load balancing
     

     In the Select DB Instance drop-down list, select the instances for load balancing.

     

     To add new read replicas for load balancing, select the read replicas from the Select DB Instance drop-down list and click OK.

     Click OK and view DB instances for load balancing in the proxy information area.

     Figure 6 Viewing DB instances for load balancing
     

Adding a Hint to Specify the Direction that a SQL Statement Will Be Routed

Hints supported by read/write splitting are as follows:

• /*FORCE_MASTER*/: A SQL statement is routed to the primary DB instance.
• /*FORCE_SLAVE*/: A SQL statement is routed to a read replica.

• In addition to the weight distribution system of read/write splitting, hints are a useful type of SQL syntax that allows you to specify whether a SQL statement is executed on the primary DB instance or on a read replica.
• Hints are only used as routing suggestions. In non-read-only SQL and non-transaction scenarios, SQL statements cannot be routed to read replicas.