sentinel/sentinel-extension/sentinel-parameter-flow-control/README.md

Sentinel Parameter Flow Control

This component provides functionality of flow control by frequent (“hot spot”) parameters.

Usage

To use Sentinel Parameter Flow Control, you need to add the following dependency to pom.xml:

<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-parameter-flow-control</artifactId>
    <version>x.y.z</version>
</dependency>

First you need to pass parameters with the following SphU.entry overloaded methods:

public static Entry entry(String name, EntryType type, int count, Object... args) throws BlockException

public static Entry entry(Method method, EntryType type, int count, Object... args) throws BlockException

For example, if there are two parameters to provide, you can:

// paramA in index 0, paramB in index 1.
SphU.entry(resourceName, EntryType.IN, 1, paramA, paramB);

Then you can configure parameter flow control rules via loadRules method in ParamFlowRuleManager:

// QPS mode, threshold is 5 for every frequent "hot spot" parameter in index 0 (the first arg).
ParamFlowRule rule = new ParamFlowRule(RESOURCE_KEY)
    .setParamIdx(0)
    .setCount(5);
// We can set threshold count for specific parameter value individually.
// Here we add an exception item. That means: QPS threshold of entries with parameter `PARAM_B` (type: int)
// in index 0 will be 10, rather than the global threshold (5).
ParamFlowItem item = new ParamFlowItem().setObject(String.valueOf(PARAM_B))
    .setClassType(int.class.getName())
    .setCount(10);
rule.setParamFlowItemList(Collections.singletonList(item));
ParamFlowRuleManager.loadRules(Collections.singletonList(rule));

The description for fields of ParamFlowRule:

Field	Description	Default
resource	resource name (required)
count	flow control threshold (required)
grade	metric type (QPS or thread count)	QPS mode
paramIdx	the index of provided parameter in SphU.entry(xxx, args) (required)
paramFlowItemList	the exception items of parameter; you can set threshold to a specific parameter value

Now the parameter flow control rules will take effect.