Configuring DWS Exception Rules

Feature Description

Some complex statements may consume a large number of resources for computing, leading to performance deterioration of the entire DWS database. To maintain system stability, DWS allows you to customize exception rules, and terminate/downgrade the tasks that hit the rules.

You can use SQL syntax to configure exception rules based on your resource and workload conditions, and associate the rules with resource pools. The system has a default exception rule to maintain stability when resources are insufficient, in case no user-defined rule is set up.

Notes and Constraints

• Clusters version 8.2.0 or later can handle exception rules. For setting exception rules on a single DN's maximum bandwidth, you need cluster version 8.2.1 or later.
• Cluster version 8.2.1 supports downgrading of exception rules (note that Storage-Compute Decoupled clusters do not). All exception rules are compatible with downgrading behavior. After downgrading, only network resource preemption is affected, lowering its priority. Downgraded network queries will only be scheduled when there are no normal queries in the system.
• The default exception rules are supported only by clusters of version 8.2.0 or later. After a cluster of an earlier version is upgraded to version 8.2.0 or later, the default exception rules do not take effect. You can create exception rules as needed.
• The default exception rule default_memsize is added to the cluster version 9.1.0.100, but it takes effect only in the newly installed cluster version 9.1.0.100 or later. When the cluster is upgraded to 9.1.0.100 or later, the default exception rules do not take effect. You can create rules as required.
• A resource pool can be associated with multiple groups of exception rules, which work in an OR way. One group of exception rules works if all its conditions are met. For example, a resource pool is associated with two groups of rules. One group specifies elapsedtime=2400, and the other group specifies elapsedtime=1200 and memsize=2000. If the execution time of a job reaches 1200 seconds and the memory usage reaches 2,000 MB, or if the execution time reaches 2,400 seconds, the job will be terminated.
• Rules in the same exception rule group take effect only if all the conditions are met. For example, if you set elapsedtime=1000 and memsize=500, it indicates that a job is terminated only if its execution time reaches 1,000 seconds and its memory usage reaches 500 MB. If only one of the thresholds is reached, the job will not be terminated.
• The default exception rules take effect for users not associated with any resource pools, and for users whose resource pools do not have any exception rules configured. If a user-defined rule is associated with a resource pool, this rule prevails in the pool.

Adding an Exception Rule

1. Log in to the DWS console.
2. In the cluster list, click the name of the target cluster to go to the Cluster Information page.
3. In the navigation pane, choose Manage Workload.
4. Click the Exception Rule tab and click Add. Set the parameters listed in Table 2.
   Figure 1 Adding an exception rule
   

5. Click OK. An exception rule does not take effect immediately after being created. You need to bind it to a resource pool. For details, see 7.

Exception Rule Management Operations

1. Log in to the DWS console.
2. In the cluster list, click the name of the target cluster to go to the Cluster Information page.
3. In the navigation pane, choose Manage Workload.
4. Click the Exception Rule tab, and edit or delete exception rules. Table 3 Exception rule management operations lists the operations.

   Table 1 Exception rule management operations

   Operation	Description
   Edit	Locate an exception rule and click Edit in the Operation column. In the displayed dialog box, modify the exception rule. For details, see Table 2. To modify an exception rule, remove or set its threshold value to -1 if you wish to delete it.
   Delete	Locate an exception rule and click Delete in the Operation column. If an exception rule has been bound to an existing resource pool, the exception rule cannot be deleted. You need to unbind the exception rule from the resource pool before deleting it.

5. Click OK.

User-defined Exception Rules and Default Exception Rules

The following table describes the user-defined exception rules and default exception rules supported by the current DWS version.