Auto Flow Control

Auto Flow Control helps ensure availability of your workloads. It restricts the execution of SQL statements during peak hours or when there are read/write exceptions by limiting how many SQL statements can be executed at the same time.

After it is enabled, the system performs flow control on sessions when the criteria you specify for your instance are met (for example, the number of active connections to your instance exceeds the Max. Active Connections parameter value).

To use this function, subscribe to Intelligent O&M first.

Constraints

To use auto flow control, contact customer service to apply for required permissions.

Procedure

Log in to the management console.
Click in the upper left corner and select a region and a project.
Click in the upper left corner of the page and choose Databases > Relational Database Service.
On the Instances page, click the DB instance name.
In the navigation pane, choose DBA Assistant > Historical Diagnosis.
Choose SQL Explorer > Auto Flow Control.
Click Auto Flow Control.

Toggle on

and configure required parameters. For details about the parameters, see Table 1.

Example for setting Auto Flow Control parameters

Set Time Window to 15:00-18:00, Max. Duration to Last 5 minutes, vCPU usage ≥ to 90%, Active sessions ≥ to 20, and and Duration (min) to 5. When all the criteria are met, Auto Flow Control is triggered. If your vCPU usage or number of active sessions falls below the threshold during the time window, flow control ends.

Figure 1 Example
Click to enlarge

**Table 1** Parameter description
Parameter	Description
Database	The name of the database for which auto flow control needs to be enabled. Ensure that the database you select is consistent with the one specified in your SQL statements, or the auto flow control policy will fail.
Username	The name of the user that auto flow control is applied.
Time Window	The time when flow control is applied. Auto flow control can be triggered only once within the time window.
Max. Duration	Maximum length of time that SQL statements matching the auto flow control policy can be throttled within the time window.
vCPU usage	vCPU usage threshold for the instance. You also need to specify the relationship between the vCPU usage and active sessions. Their relationship can be and or or.
Active sessions	Threshold for active sessions. Value range: 1 to 5000
Duration (min)	How long the vCPU usage and active sessions exceed the specified values. For example, if you set vCPU usage ≥ to 90%, Active sessions ≥ to 1000, and Duration (min) to 30, auto flow control will be triggered only when the vCPU usage and active sessions exceed 90% and 1,000 for 30 minutes.
Max. Active Connections	Maximum number of active connections allowed. Value range: 1 to 5000 For example, if you set Max. Active Connections to 500, the system will automatically end some active connections when necessary to keep the number of active sessions within 500.