频繁产生对象造成gc时间过长案例分析

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发布于 2018-09-17 16:11:46

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发布于 2018-09-17 16:11:46

文章被收录于专栏：码匠的流水账码匠的流水账

序

本文主要分析一个频繁产生对象造成gc时间过长的case。

症状及分析

gc时间过长，平均gc pause的时间要将近4秒，有13%的gc超过10秒，太可怕了，部分gc日志如下：

[PSYoungGen: 457878K->126656K(489472K)] 1746043K->1453131K(1887744K), 12.1965757 secs] [Times: user=5.59 sys=0.52, real=12.19 secs] 
154415.774: [GC (Allocation Failure) 
Desired survivor size 212860928 bytes, new threshold 1 (max 15)
[PSYoungGen: 376192K->65968K(484864K)] 1702667K->1392499K(1883136K), 0.1665513 secs] [Times: user=0.10 sys=0.00, real=0.17 secs] 
154416.838: [GC (Allocation Failure) 
Desired survivor size 235929600 bytes, new threshold 1 (max 15)
[PSYoungGen: 341424K->196182K(445952K)] 1667955K->1523034K(1844224K), 1.7996294 secs] [Times: user=0.89 sys=0.03, real=1.80 secs] 
154419.456: [GC (Allocation Failure) 
Desired survivor size 225968128 bytes, new threshold 1 (max 15)
[PSYoungGen: 434262K->121776K(468480K)] 1761114K->1486938K(1866752K), 23.0844304 secs] [Times: user=10.75 sys=0.81, real=23.09 secs] 
154442.541: [Full GC (Ergonomics) [PSYoungGen: 121776K->0K(468480K)] [ParOldGen: 1365162K->208108K(1398272K)] 1486938K->208108K(1866752K), [Metaspace: 93615K->93615K(1132544K)], 23.5955214 secs] [Times: user=3.76 sys=5.30, real=23.59 secs] 
154504.670: [GC (Allocation Failure) 
Desired survivor size 217579520 bytes, new threshold 1 (max 15)
[PSYoungGen: 200553K->106368K(486400K)] 408662K->314476K(1884672K), 1.0664613 secs] [Times: user=0.39 sys=0.13, real=1.06 secs] 
154507.542: [GC (Allocation Failure) 
Desired survivor size 218103808 bytes, new threshold 1 (max 15)
[PSYoungGen: 372096K->144182K(478208K)] 580204K->425927K(1876480K), 5.7999561 secs] [Times: user=1.12 sys=1.55, real=5.80 secs] 
154514.037: [GC (Allocation Failure) 
Desired survivor size 213909504 bytes, new threshold 1 (max 15)
[PSYoungGen: 409910K->87920K(489984K)] 691655K->407999K(1888256K), 10.1020217 secs] [Times: user=4.46 sys=0.61, real=10.11 secs] 
154563.240: [GC (Allocation Failure) 
Desired survivor size 213385216 bytes, new threshold 1 (max 15)
[PSYoungGen: 328380K->65952K(485888K)] 648460K->386087K(1884160K), 0.0918412 secs] [Times: user=0.04 sys=0.01, real=0.09 secs] 
154564.037: [GC (Allocation Failure) 
Desired survivor size 219676672 bytes, new threshold 1 (max 15)
[PSYoungGen: 342944K->153558K(478208K)] 663079K->474022K(1876480K), 3.1948641 secs] [Times: user=0.72 sys=0.69, real=3.19 secs] 
154568.135: [GC (Allocation Failure) 
Desired survivor size 212336640 bytes, new threshold 1 (max 15)
[PSYoungGen: 423382K->98528K(484352K)] 743846K->457302K(1882624K), 13.4085860 secs] [Times: user=6.04 sys=0.69, real=13.41 secs]

通过jmap dump下内存之后，使用mat分享，查看thread_overview

可以看到ElasticsearchJestHealthIndicator.doHealthCheck持有了很多对象没释放

调试及复现

本地复现

spring-context-4.3.7.RELEASE-sources.jar!/org/springframework/jmx/export/SpringModelMBean.java

    /**
     * Switches the {@link Thread#getContextClassLoader() context ClassLoader} for the
     * managed resources {@link ClassLoader} before allowing the invocation to occur.
     * @see javax.management.modelmbean.ModelMBean#invoke
     */
    @Override
    public Object invoke(String opName, Object[] opArgs, String[] sig)
            throws MBeanException, ReflectionException {

        ClassLoader currentClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(this.managedResourceClassLoader);
            return super.invoke(opName, opArgs, sig);
        }
        finally {
            Thread.currentThread().setContextClassLoader(currentClassLoader);
        }
    }

spring-boot-actuator-1.4.5.RELEASE-sources.jar!/org/springframework/boot/actuate/endpoint/jmx/DataEndpointMBean.java

@ManagedResource
public class DataEndpointMBean extends EndpointMBean {

    /**
     * Create a new {@link DataEndpointMBean} instance.
     * @param beanName the bean name
     * @param endpoint the endpoint to wrap
     * @param objectMapper the {@link ObjectMapper} used to convert the payload
     */
    public DataEndpointMBean(String beanName, Endpoint<?> endpoint,
            ObjectMapper objectMapper) {
        super(beanName, endpoint, objectMapper);
    }

    @ManagedAttribute(description = "Invoke the underlying endpoint")
    public Object getData() {
        return convert(getEndpoint().invoke());
    }

}

系本地idea开启了Enable JMX Agent才可以复现

healthEndpoint

spring-boot-admin-server-1.4.6-sources.jar!/de/codecentric/boot/admin/registry/StatusUpdateApplicationListener.java

    private long updatePeriod = 10_000L;

    public void startStatusUpdate() {
        if (scheduledTask != null && !scheduledTask.isDone()) {
            return;
        }

        scheduledTask = taskScheduler.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                statusUpdater.updateStatusForAllApplications();
            }
        }, updatePeriod);
        LOGGER.debug("Scheduled status-updater task for every {}ms", updatePeriod);

    }

spring-boot-admin-server-1.4.6-sources.jar!/de/codecentric/boot/admin/registry/StatusUpdater.java

    public void updateStatusForAllApplications() {
        long now = System.currentTimeMillis();
        for (Application application : store.findAll()) {
            if (now - statusLifetime > application.getStatusInfo().getTimestamp()) {
                updateStatus(application);
            }
        }
    }

    public void updateStatus(Application application) {
        StatusInfo oldStatus = application.getStatusInfo();
        StatusInfo newStatus = queryStatus(application);

        Application newState = Application.create(application).withStatusInfo(newStatus).build();
        store.save(newState);

        if (!newStatus.equals(oldStatus)) {
            publisher.publishEvent(
                    new ClientApplicationStatusChangedEvent(newState, oldStatus, newStatus));
        }
    }

    protected StatusInfo queryStatus(Application application) {
        LOGGER.trace("Updating status for {}", application);

        try {
            @SuppressWarnings("unchecked")
            ResponseEntity<Map<String, Object>> response = restTemplate.getForEntity(
                    application.getHealthUrl(), (Class<Map<String, Object>>) (Class<?>) Map.class);
            LOGGER.debug("/health for {} responded with {}", application, response);

            if (response.hasBody() && response.getBody().get("status") instanceof String) {
                return StatusInfo.valueOf((String) response.getBody().get("status"));
            } else if (response.getStatusCode().is2xxSuccessful()) {
                return StatusInfo.ofUp();
            } else {
                return StatusInfo.ofDown();
            }

        } catch (Exception ex) {
            if ("OFFLINE".equals(application.getStatusInfo().getStatus())) {
                LOGGER.debug("Couldn't retrieve status for {}", application, ex);
            } else {
                LOGGER.warn("Couldn't retrieve status for {}", application, ex);
            }
            return StatusInfo.ofOffline();
        }
    }

可以看到这个admin-server注册了个定时任务，定时调用/health

问题分析

ElasticsearchHealthIndicatorConfiguration

spring-boot-actuator-1.4.5.RELEASE-sources.jar!/org/springframework/boot/actuate/autoconfigure/ElasticsearchHealthIndicatorConfiguration.java

class ElasticsearchHealthIndicatorConfiguration {

    @Configuration
    @ConditionalOnBean(Client.class)
    @ConditionalOnEnabledHealthIndicator("elasticsearch")
    @EnableConfigurationProperties(ElasticsearchHealthIndicatorProperties.class)
    static class ElasticsearchClientHealthIndicatorConfiguration extends
            CompositeHealthIndicatorConfiguration<ElasticsearchHealthIndicator, Client> {

        private final Map<String, Client> clients;

        private final ElasticsearchHealthIndicatorProperties properties;

        ElasticsearchClientHealthIndicatorConfiguration(Map<String, Client> clients,
                ElasticsearchHealthIndicatorProperties properties) {
            this.clients = clients;
            this.properties = properties;
        }

        @Bean
        @ConditionalOnMissingBean(name = "elasticsearchHealthIndicator")
        public HealthIndicator elasticsearchHealthIndicator() {
            return createHealthIndicator(this.clients);
        }

        @Override
        protected ElasticsearchHealthIndicator createHealthIndicator(Client client) {
            return new ElasticsearchHealthIndicator(client, this.properties);
        }

    }

    @Configuration
    @ConditionalOnBean(JestClient.class)
    @ConditionalOnEnabledHealthIndicator("elasticsearch")
    static class ElasticsearchJestHealthIndicatorConfiguration extends
            CompositeHealthIndicatorConfiguration<ElasticsearchJestHealthIndicator, JestClient> {

        private final Map<String, JestClient> clients;

        ElasticsearchJestHealthIndicatorConfiguration(Map<String, JestClient> clients) {
            this.clients = clients;
        }

        @Bean
        @ConditionalOnMissingBean(name = "elasticsearchHealthIndicator")
        public HealthIndicator elasticsearchHealthIndicator() {
            return createHealthIndicator(this.clients);
        }

        @Override
        protected ElasticsearchJestHealthIndicator createHealthIndicator(
                JestClient client) {
            return new ElasticsearchJestHealthIndicator(client);
        }

    }

}

ElasticsearchHealthIndicator

spring-boot-actuator-1.4.5.RELEASE-sources.jar!/org/springframework/boot/actuate/health/ElasticsearchHealthIndicator.java

    @Override
    protected void doHealthCheck(Health.Builder builder) throws Exception {
        List<String> indices = this.properties.getIndices();
        ClusterHealthResponse response = this.client.admin().cluster()
                .health(Requests.clusterHealthRequest(indices.isEmpty() ? allIndices
                        : indices.toArray(new String[indices.size()])))
                .actionGet(this.properties.getResponseTimeout());

        switch (response.getStatus()) {
        case GREEN:
        case YELLOW:
            builder.up();
            break;
        case RED:
        default:
            builder.down();
            break;
        }
        builder.withDetail("clusterName", response.getClusterName());
        builder.withDetail("numberOfNodes", response.getNumberOfNodes());
        builder.withDetail("numberOfDataNodes", response.getNumberOfDataNodes());
        builder.withDetail("activePrimaryShards", response.getActivePrimaryShards());
        builder.withDetail("activeShards", response.getActiveShards());
        builder.withDetail("relocatingShards", response.getRelocatingShards());
        builder.withDetail("initializingShards", response.getInitializingShards());
        builder.withDetail("unassignedShards", response.getUnassignedShards());
    }

spring-boot-actuator-1.4.5.RELEASE-sources.jar!/org/springframework/boot/actuate/health/ElasticsearchHealthIndicatorProperties.java

@ConfigurationProperties(prefix = "management.health.elasticsearch", ignoreUnknownFields = false)
public class ElasticsearchHealthIndicatorProperties {

    /**
     * Comma-separated index names.
     */
    private List<String> indices = new ArrayList<String>();

    /**
     * Time, in milliseconds, to wait for a response from the cluster.
     */
    private long responseTimeout = 100L;

    //......

}

如果有指定indices，则会查询他们的健康情况，比如/index1,index2/_stats，如果没有则查询所有的indices，这个就是个潜在的坑。

ElasticsearchJestHealthIndicator

spring-boot-actuator-1.4.5.RELEASE-sources.jar!/org/springframework/boot/actuate/health/ElasticsearchJestHealthIndicator.java

    @Override
    protected void doHealthCheck(Health.Builder builder) throws Exception {
        JestResult aliases = this.jestClient.execute(new Stats.Builder().build());
        JsonElement root = this.jsonParser.parse(aliases.getJsonString());
        JsonObject shards = root.getAsJsonObject().get("_shards").getAsJsonObject();
        int failedShards = shards.get("failed").getAsInt();
        if (failedShards != 0) {
            builder.outOfService();
        }
        else {
            builder.up();
        }
    }

jest最后发出的http请求是/_all/_stats，这个就是问题所在，查询所有_all的统计数据，对于一个大的elasticsearch平台来说，返回的数据是巨大的，将近5000条数据，返回的json纯文件都要20多M，这个再加上定时任务/health查询，导致新生对象不断产生，ygc非常频繁，造成内存泄露的现象。

小结

定时监控应用health是个好东东，但是得注意频率，另外还得关注具体实现，像elasticsearch的这个稍不注意就被坑了，相当于定时产生一定量的垃圾，频率超过垃圾回收的速度，类似内存泄露，给应用gc带来很大的负担。

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