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Refactor degrade hierarchy with new circuit breaker mechanism and imp…
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…rove strategy

* Add `CircuitBreaker` abstraction (with half-open state) and add circuit breaker state change event observer support.
* Improve circuit breaking strategy (avg RT → slow request ratio) and make statistics of each rule dependent (to support arbitrary statistic interval).
* Add simple "trial" mechanism (aka. half-open).
* Refactor mechanism of metric recording and state change handling for circuit breakers: record RT and error when requests have completed (i.e. `onExit`, based on alibaba#1420).

Signed-off-by: Eric Zhao <[email protected]>
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@sczyh30
sczyh30 committed Jul 30, 2020
1 parent 1c49297 commit bc9cfb3
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165 changes: 46 additions & 119 deletions sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/degrade/DegradeRule.java
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Original file line number Diff line number Diff line change
Expand Up @@ -15,19 +15,12 @@
*/
package com.alibaba.csp.sentinel.slots.block.degrade;

import com.alibaba.csp.sentinel.concurrent.NamedThreadFactory;
import com.alibaba.csp.sentinel.context.Context;
import com.alibaba.csp.sentinel.node.ClusterNode;
import com.alibaba.csp.sentinel.node.DefaultNode;
import com.alibaba.csp.sentinel.slots.block.AbstractRule;
import com.alibaba.csp.sentinel.slots.block.RuleConstant;
import com.alibaba.csp.sentinel.slots.clusterbuilder.ClusterBuilderSlot;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.Objects;

/**
* <p>
Expand All @@ -52,47 +45,45 @@
* </ul>
*
* @author jialiang.linjl
* @author Eric Zhao
*/
public class DegradeRule extends AbstractRule {

@SuppressWarnings("PMD.ThreadPoolCreationRule")
private static ScheduledExecutorService pool = Executors.newScheduledThreadPool(
Runtime.getRuntime().availableProcessors(), new NamedThreadFactory("sentinel-degrade-reset-task", true));

public DegradeRule() {}

public DegradeRule(String resourceName) {
setResource(resourceName);
}

/**
* RT threshold or exception ratio threshold count.
* Circuit breaking strategy (0: average RT, 1: exception ratio, 2: exception count).
*/
private double count;
private int grade = RuleConstant.DEGRADE_GRADE_RT;

/**
* Degrade recover timeout (in seconds) when degradation occurs.
* Threshold count.
*/
private int timeWindow;
private double count;

/**
* Degrade strategy (0: average RT, 1: exception ratio, 2: exception count).
* Recovery timeout (in seconds) when circuit breaker opens. After the timeout, the circuit breaker will
* transform to half-open state for trying a few requests.
*/
private int grade = RuleConstant.DEGRADE_GRADE_RT;
private int timeWindow;

/**
* Minimum number of consecutive slow requests that can trigger RT circuit breaking.
* Minimum number of requests (in an active statistic time span) that can trigger circuit breaking.
*
* @since 1.7.0
*/
private int rtSlowRequestAmount = RuleConstant.DEGRADE_DEFAULT_SLOW_REQUEST_AMOUNT;
private int minRequestAmount = RuleConstant.DEGRADE_DEFAULT_MIN_REQUEST_AMOUNT;

/**
* Minimum number of requests (in an active statistic time span) that can trigger circuit breaking.
*
* @since 1.7.0
* The threshold of slow request ratio in RT mode.
*/
private int minRequestAmount = RuleConstant.DEGRADE_DEFAULT_MIN_REQUEST_AMOUNT;
private double slowRatioThreshold = 1.0d;

private int statIntervalMs = 1000;

public int getGrade() {
return grade;
Expand Down Expand Up @@ -121,21 +112,30 @@ public DegradeRule setTimeWindow(int timeWindow) {
return this;
}

public int getRtSlowRequestAmount() {
return rtSlowRequestAmount;
public int getMinRequestAmount() {
return minRequestAmount;
}

public DegradeRule setRtSlowRequestAmount(int rtSlowRequestAmount) {
this.rtSlowRequestAmount = rtSlowRequestAmount;
public DegradeRule setMinRequestAmount(int minRequestAmount) {
this.minRequestAmount = minRequestAmount;
return this;
}

public int getMinRequestAmount() {
return minRequestAmount;
public double getSlowRatioThreshold() {
return slowRatioThreshold;
}

public DegradeRule setMinRequestAmount(int minRequestAmount) {
this.minRequestAmount = minRequestAmount;
public DegradeRule setSlowRatioThreshold(double slowRatioThreshold) {
this.slowRatioThreshold = slowRatioThreshold;
return this;
}

public int getStatIntervalMs() {
return statIntervalMs;
}

public DegradeRule setStatIntervalMs(int statIntervalMs) {
this.statIntervalMs = statIntervalMs;
return this;
}

Expand All @@ -144,23 +144,19 @@ public boolean equals(Object o) {
if (this == o) { return true; }
if (o == null || getClass() != o.getClass()) { return false; }
if (!super.equals(o)) { return false; }
DegradeRule that = (DegradeRule) o;
return Double.compare(that.count, count) == 0 &&
timeWindow == that.timeWindow &&
grade == that.grade &&
rtSlowRequestAmount == that.rtSlowRequestAmount &&
minRequestAmount == that.minRequestAmount;
DegradeRule rule = (DegradeRule)o;
return Double.compare(rule.count, count) == 0 &&
timeWindow == rule.timeWindow &&
grade == rule.grade &&
minRequestAmount == rule.minRequestAmount &&
Double.compare(rule.slowRatioThreshold, slowRatioThreshold) == 0 &&
statIntervalMs == rule.statIntervalMs;
}

@Override
public int hashCode() {
int result = super.hashCode();
result = 31 * result + new Double(count).hashCode();
result = 31 * result + timeWindow;
result = 31 * result + grade;
result = 31 * result + rtSlowRequestAmount;
result = 31 * result + minRequestAmount;
return result;
return Objects.hash(super.hashCode(), count, timeWindow, grade, minRequestAmount,
slowRatioThreshold, statIntervalMs);
}

@Override
Expand All @@ -171,84 +167,15 @@ public String toString() {
", count=" + count +
", limitApp=" + getLimitApp() +
", timeWindow=" + timeWindow +
", rtSlowRequestAmount=" + rtSlowRequestAmount +
", minRequestAmount=" + minRequestAmount +
"}";
", slowRatioThreshold=" + slowRatioThreshold +
", statIntervalMs=" + statIntervalMs +
'}';
}

// Internal implementation (will be deprecated and moved outside).

private AtomicLong passCount = new AtomicLong(0);
private final AtomicBoolean cut = new AtomicBoolean(false);

@Override
public boolean passCheck(Context context, DefaultNode node, int acquireCount, Object... args) {
if (cut.get()) {
return false;
}

ClusterNode clusterNode = ClusterBuilderSlot.getClusterNode(this.getResource());
if (clusterNode == null) {
return true;
}

if (grade == RuleConstant.DEGRADE_GRADE_RT) {
double rt = clusterNode.avgRt();
if (rt < this.count) {
passCount.set(0);
return true;
}

// Sentinel will degrade the service only if count exceeds.
if (passCount.incrementAndGet() < rtSlowRequestAmount) {
return true;
}
} else if (grade == RuleConstant.DEGRADE_GRADE_EXCEPTION_RATIO) {
double exception = clusterNode.exceptionQps();
double success = clusterNode.successQps();
double total = clusterNode.totalQps();
// If total amount is less than minRequestAmount, the request will pass.
if (total < minRequestAmount) {
return true;
}

// In the same aligned statistic time window,
// "success" (aka. completed count) = exception count + non-exception count (realSuccess)
double realSuccess = success - exception;
if (realSuccess <= 0 && exception < minRequestAmount) {
return true;
}

if (exception / success < count) {
return true;
}
} else if (grade == RuleConstant.DEGRADE_GRADE_EXCEPTION_COUNT) {
double exception = clusterNode.totalException();
if (exception < count) {
return true;
}
}

if (cut.compareAndSet(false, true)) {
ResetTask resetTask = new ResetTask(this);
pool.schedule(resetTask, timeWindow, TimeUnit.SECONDS);
}

@Deprecated
public boolean passCheck(Context context, DefaultNode node, int count, Object... args) {
return false;
}

private static final class ResetTask implements Runnable {

private DegradeRule rule;

ResetTask(DegradeRule rule) {
this.rule = rule;
}

@Override
public void run() {
rule.passCount.set(0);
rule.cut.set(false);
}
}
}
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